Digital Technology - Paper 3

B

The binary equivalent of the number 12 is A. 1010. B. 1100. C. 0011. D. 0101.

C

Two CCDs are identical in all respects except the pixels of one device have a greater quantum efficiency. This device will A. have a greater magnification. B. have a greater resolution. C. be able to record images at lower light levels. D. use less energy.

1. (a) (cassette) tape / LP / vinyl; 1 (b) Isobel's/analogue recording expected to fall in quality whereas digital/Claire's recording expected to maintain quality; analogue process of retrieval affects quality of future retrievals / OWTTE; 2 (c) number of bits = 30 × 60 × 40 × 103 × 2 × 16; number of bits = 2.3 × 109 (= 288 Mbytes); 2 [5]

1. This question is about analogue and digital storage. As part of a physics lesson, Isobel and Claire each make an audio recording of their teacher. They then compare the quality of their recordings. Isobel's recording is in analogue format whereas Claire's recording is digital and stored on a CD. (a) State one possible analogue method of storage used by Isobel. ...................................................................................................................................... (1) (b) The first time the recordings are played, their qualities are identical. Outline whether the quality of each recording is expected to remain the same after many uses. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (c) Use the following information to determine the number of bits used in Claire's digital recording. Total time of recording = 30 minutes Sampling frequency = 40 kHz Format of recording = Stereo (2 channels) Number of bits per sample = 16 ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 5 marks)

10. (a) silicon chip divided into separate areas; each of these areas is a pixel; each pixel behaves as a capacitor; 3 (b) (i) area of pixel = ; 2.86 × 10-6 cm2 separation = = 1.7 × 10-3 cm; 2 (ii) points on image must be about 2 × 1.7 × 10-3 cm apart; separation of objects = = 0.11cm; 2 [7]

10. This question is about a digital camera. (a) By reference to what is meant by a pixel, describe the structure of a charge-coupled device (CCD). ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (b) The CCD in a camera has an area of 16 cm2 and is divided into 5.6 megapixels. The camera is used to take a photograph with a linear magnification of 0.030. (i) Calculate the separation of pixels on the CCD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Determine the minimum separation of two points on an object such that they may be seen separately on the image. Diffraction effects at the lens may be ignored. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 7 marks)

11. (a) gain = 1 + ; gain = 11; 2 (b) for saturation, VOUT = 9V; VIN = = 0.82 V ; 2 [4]

11. This question is about an operational amplifier (op-amp) circuit. The circuit diagram is for a non-inverting amplifier. The operational amplifier is ideal. Calculate the (a) gain of the amplifier circuit. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) input potential VIN at which the amplifier saturates. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 4 marks)

12. cellular exchange receives signal from base stations; computer monitors signal strength; selects base station with strongest signal; routes call from base station to PSTN; 4 [4]

12. This question is about a mobile phone network. Describe the role of the cellular exchange during the making of a call from a mobile phone. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (Total 4 marks)

C

13. What is the value of the binary number 11001 in decimal notation? A. 50 B. 38 C. 25 D. 19 (Total 1 mark)

B

14. A CCD camera is used to capture the image of a painting. The area of the painting is 2.0 m2 and the area of the image is 50 mm2. Which of the following is the linear magnification of the image? A. 2.5 × 10-5 B. 5.0 × 10-3 C. 2.0 × 102 D. 4.0 × 104 (Total 1 mark)

A

15. An analogue signal is sampled at time intervals t. Each sample is converted to a digital number having n bits. What is the total number of bits produced in a time T? A. B. C. ntT D. (Total 1 mark)

16. (a) more easily reproduced; more accurately reproduced; noise can be removed; (do not accept just noise) higher retrieval speed; smaller space required for same amount of data; any other sensible storage-related advantage; 2 max (b) photons cause the creation/produce/give rise to electron-hole pairs (in the pixel); the electrons/holes migrate to the relevant electrode; leads to the build-up of charge on the electrodes (producing a change in voltage across the pixel); 3 (c) (i) energy of one photon = 6.6 × 10-34 × 7.2 × 1014 = 4.75 × 10-19 (J) ; max number in 18 ms = ; (= 1.2 × 104) 2 (ii) change in charge = (1.0 × 10-5 × 1.2 × 10-11 =) 1.2 × 10-16 (C); number of photons needed = 0.75 × 103; quantum efficiency = 0.063 or 6.3 %; 3 [10]

16. This question is about charge-coupled device (CCD). (a) State two advantages of storing information in a digital form rather than an analogue form. 1. .................................................................................................................................. ...................................................................................................................................... 2. .................................................................................................................................. ...................................................................................................................................... (2) (b) A CCD is effectively a silicon chip that is divided into small areas called pixels. Each pixel is provided with electrodes. Outline how light incident on a pixel produces a change in potential difference across the pixel. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (c) Light of frequency 7.2 × 1014 Hz and intensity 1.6 mW m-2 is incident on a pixel for a time of 18 ms. The area of the pixel is 2.0 × 10-10 m2 and its capacitance is 12 pF. The resulting change in potential difference across the pixel is 10 μV. (i) Deduce that the number of photons incident on the pixel is 1.2 × 104. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Determine the quantum efficiency of the pixel. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (Total 10 marks)

17. (a) analogue: continuously variable (between two limits); digital: two states only / discrete; 2 (b) (i) e.g. video tapes / LPs; 1 (ii) e.g. floppy discs / CDs; 1 (c) reason: better quality reproduction; explanation: because noise can be eliminated / signals can be re-shaped; reason: faster retrieval; explanation: switching on-off only; reason: ease of portability; explanation: high density of information storage / little physical space required for storage; 4 max Accept any two of the above reason and explanation. (d) amount of data generated increasing rapidly, so harder to store; difficult to catalogue so much information; personal data can be easily stored and accessed; flawless copying leads to increased piracy / copyright issues; requires many data centres that consume a lot of power; data needs to be backed up in case of hardware/software failure; one mouse click can lose huge amount of data; ease of losing portable data storage devices; 2 max Accept any other sensible suggestion. [10]

17. This question is about storing information. Information may be stored either in analogue form or in digital form. (a) Distinguish between analogue information and digital information. Analogue: .................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... Digital: ........................................................................................................................ ...................................................................................................................................... ...................................................................................................................................... (2) (b) State one method by which information may be stored in (i) analogue form. ........................................................................................................................... (1) (ii) digital form. ........................................................................................................................... (1) (c) State and explain two reasons why, for many purposes, digital storage of information is replacing analogue storage. 1: ................................................................................................................................. ...................................................................................................................................... ...................................................................................................................................... 2: ................................................................................................................................. ...................................................................................................................................... ...................................................................................................................................... (4) (d) Suggest two possible implications for society of the ever-increasing capability of data storage. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 10 marks)

18. (a) gain = 1 + ; = 1 + = 6; 2 (b) (i) 5.4 V; negative; 2 (ii) 9.0 V; 1 [5]

18. This question is about an amplifier circuit. The diagram below shows an amplifier circuit incorporating an ideal operational amplifier (op-amp). The operational amplifier uses a +9 V / 0 / -9 V supply. (a) Calculate the gain of the amplifier circuit. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) Determine the output potential Vout for values of input potential Vin equal to (i) -0.9 V. ........................................................................................................................... ........................................................................................................................... (2) (ii) +2.0 V. ........................................................................................................................... (1) (Total 5 marks)

19. when switched on, phone sends out (identifying) signal; picked up by base stations; communicated by base stations to cellular exchange; computer at cellular exchange; selects base station with strongest signal; allocates carrier wave frequency / channel; and time slot; 5 max [5]

19. This question is about a mobile phone network. Describe the role of base stations and a cellular exchange when a mobile phone is switched on and before a call is made. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (Total 5 marks)

2. (a) magnification = ; = 5.0 × 10-6; 2 Award [2] for bald correct answer. (b) distance between pixels = = 6 × 10-6 m; resolution = = 1.2m; 2 Also allow 2.4 m for candidates who assume that objects need to be separated by two pixels to be completely resolved. (c) no effect; 1 [5]

2. This question is about charge-coupled devices (CCDs). An image of the surface of the Earth is recorded by a digital camera from an aeroplane. Each image covers 144 km2 of the Earth's surface and is recorded by a square CCD of area 36 cm2. (a) Calculate the magnification of the system. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) The CCD contains 1.0 × 108 pixels. Deduce the minimum distance between two points on Earth that can be resolved by this camera. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (c) It is proposed to improve the quantum efficiency of the CCD. State the effect, if any, on the resolution of the system. ...................................................................................................................................... ...................................................................................................................................... (1) (Total 5 marks)

C

20. For the five-bit binary number 11010, which of the following correctly identifies both the most-significant bit (MSB) and the equivalent decimal number? MSB Decimal A. 1 52 B. 0 26 C. 1 26 D. 0 52 (Total 1 mark)

(a) maximum two sensible suggestions related to image capture: e.g. much higher quantum efficiency / more sensitive to light than film; much shorter exposure times than film; sensitive to wider spectrum than film; no moving parts required in device; digital storage advantage; any other image capture advantage; 2 max Only accept one advantage of digital storage, e.g. compact storage (b) 26 0002 pixels in one image; 26 0002 × 16 = 1.08 × 1010 bits per image; = 36 or 37; 3 (c) (i) individual pixel/element is a capacitor; (X-ray) photons release electrons/charge carriers; 2 (ii) each voltage is digitized; pd/voltage across pixel is proportional to intensity; position of each pixel is recorded together with digitized voltage; 3 [10]

23. This question is about charge-coupled devices (CCDs). (a) List two advantages of using CCDs as compared to using film for image capture. 1: .................................................................................................................................. ...................................................................................................................................... 2: .................................................................................................................................. ...................................................................................................................................... (2) (b) A CCD used to capture X-ray images consists of a square 26000 × 26000 arrangement of pixels. Each pixel produces 16 levels of information. Images captured by the CCD are stored on a disk which can store a maximum of 4.0 × 1011 bits of data. Determine the number of images that may be stored on one disk. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (c) Outline (i) how X-rays incident on a pixel in a CCD produce a voltage signal. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) how voltage signals such as that in (c)(i) are used to store the X-ray information. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (Total 10 marks)

3. (a) infinite (open loop) gain; no current drawn on inputs / infinite input resistance/impedance; 2 (b) switchover happens when non-inverting input ≥ 3 V; current through 100 kΩ = = 0.16mA; VIN = 3 + [0.16 mA × 22 kΩ] = 3 + 3.52 = 6.5 V; 3 Award [2 max] for calculating other threshold value i.e. 0.8V. (c) idea that noise and/or dispersion distort digital pulse; idea of two fixed outputs with different switch over points; link to cleaning up of signal / removal of noise / no stray pulses produced; 3 [8]

3. This question is about a Schmitt trigger. The diagram below shows a Schmitt trigger circuit based on an operational amplifier (op-amp). The output of this Schmitt trigger is positive saturation (+13 V) or negative saturation (-13 V). (a) State two properties of an ideal op-amp. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) Determine the input value that will cause the output to switch from -13 V to +13 V. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (c) Explain how a Schmitt trigger can be used to reshape a digital pulse. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (Total 8 marks)

4. (a) new base station selected and connected; 1 (b) no change; 1 [2]

4. This question is about a mobile phone network. Erin is a passenger on a train making a call to a standard fixed telephone line ("landline") from her mobile phone. The train moves Erin between adjacent communication cells. Outline the changes, if any, that take place in the (a) cellular exchange. ...................................................................................................................................... ...................................................................................................................................... (1) (b) public switched telephone network (PSTN). ...................................................................................................................................... ...................................................................................................................................... (1) (Total 2 marks)

B

5. The decimal number 18 is represented in binary by a five bit digital number. Which of the following correctly identifies the least-significant bit (LSB) and the most-significant bit (MSB) of the binary number? LSB MSB A. 0 0 B. 0 1 C. 1 0 D. 1 1 (Total 1 mark)

D

6. A CD stores digital information with a series of bumps (lands) and pits. The depth of each pit is d. Which of the following is the most appropriate wavelength of laser light to recover the information? A. B. d C. 2d D. 4d (Total 1 mark)

C

7. Which of the following digital devices is least likely to use a charge-coupled device (CCD) in its construction? A. Fax machine B. Camera C. Watch D. X-ray machine (Total 1 mark)

8. (a) the number of pixels / distance between pixels; 1 (b) the image is digital so it can be manipulated; it can show a bright object as well as a faint object accurately at the same time; it requires shorter exposure times / has greater sensitivity; responds to wider range of wavelengths; responds linearly with intensity; 1 max (c) (i) power deposited on one pixel is 5.3 × 103 × 4.2 × 10-12 (= 2.226 × 10-14 W); power = N × 6.63 × 10-34 × 3.9 × 1014(= N × 2.5857 × 10-19]; N = ; = 8.6 × 104 3 (ii) number of electrons emitted in 25 ms is (0.80 × 8.6 × 104 × 25 × 103 =1720) ≈ 1.7 × 103; and so charge is (1.7 × 103 × 1.6 × 10-19) = 2.8 × 10-16 C; 2 (iii) = 20 μV; 1 (iv) momentum of one photon 8.62 × 10-28 Ns; 1 (v) pressure = rate of change of momentum per unit area; = 1.8 × 10-11 Pa; 2 Accept unit N m-2 for Pa. [11]

8. This question is about charge-coupled devices (CCDs) and photons. (a) State one factor that affects the resolution of an image obtained with a CCD. ...................................................................................................................................... ...................................................................................................................................... (1) (b) State one advantage of a CCD image, compared to an image on ordinary photographic film. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (1) (c) Light of intensity 5.3 × 10-3 W m-2 and frequency 3.9 × 1014 Hz is incident on a pixel of a CCD. The area of the pixel is 4.2 × 10-12 m2 and the quantum efficiency is 80 %. The capacitance of the pixel is 14 pF. (i) Show that the number of photons incident on the pixel of the CCD per second is 8.6 × 104. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (ii) Calculate the charge that accumulates in the pixel during a time of 25 ms. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iii) Determine the potential difference at the ends of the pixel. ........................................................................................................................... ........................................................................................................................... (1) (iv) Calculate the momentum of one of the incident photons. ........................................................................................................................... ........................................................................................................................... (1) (v) Using your answer to (c)(iv), estimate the pressure exerted by the photons in (c)(i) on the pixel of the CCD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 11 marks)

9. (a) (i) two states only / series of "on" and "off" / ones and zeros; 1 (ii) number of bits = 2 × 16 × 44.1 × 103 × 3600; = 5.1 × 109; 2 (b) number of bits on one page = 45 × 65 × 8 ; = 2.34 × 104 number of pages = 2.2 × 105; 2 [5]

9. This question is about digital sampling. (a) A compact disc stores music in digital form. The music is sampled at a frequency of 44.1 kHz. Each sample consists of two 16-bit words. (i) State what is meant by digital form. ........................................................................................................................... ........................................................................................................................... (1) (ii) The disc stores music that takes one hour for playback. Determine the minimum number of bits that are stored on the disc. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (b) A page from a book has 45 lines of writing. Each line of the book has, on average, 65 letters and spaces. The text of the book is to be stored on compact disc where each letter or space on a line is represented by an eight-bit number. Determine the number of pages of text that can be stored on a compact disc similar to that in (a). ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 5 marks)

D

A CCD camera is used to take the picture of an object of length 30 m. The image of the object on the chip measures 0.03 mm. The magnification is A. 106. B. 103. C. 10-3. D. 10-6.

B

A compact disc player uses laser light to read a disc. The height of one pit on the CD is about of the wavelength of the laser light. The light illuminates the edge of a pit. Which of the following is correct with reference to the interference of the light and the binary information registered? Interference Binary information A. constructive 0 B. destructive 1 C. constructive 1 D. destructive 0

(a) image length / object length; 1 (b) area corresponding to each pixel separation of pixels divided by 1.5 = 0.0013 cm; the distance between two pixels < 0.0020 cm;

A digital camera is used to photograph an object. Two points on the object are separated by 0.0020 cm. The charged coupled device (CCD) in the camera has a collecting area of 16 cm2 and contains 4.0 megapixels. The magnification of the camera is 1.5. (a) Define magnification. ................................................................................................................................... ................................................................................................................................... (1) (b) Deduce that the images of the points can be resolved. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (4) (Total 5 marks)

B

A laser of wavelength λ is used in a computer to read data from a CD. Which of the following is the appropriate depth of a pit on the CD? A. wavelength/2 B. wavelength/4 C. 2*wavelength D. 4*wavelength

(a) length of pixel = separation of 5.0 104 m on CCD = 5.0 104 4.0 102 = 2.0 105 m; unlikely to be resolved as minimum of two pixels needed; 4 (b) (i) the ratio of the number electrons emitted to the number of photons incident on the pixel / OWTTE; 1 (ii) number of electrons emitted = 0.8 5.5 104; amount of charge generated on pixel = 0.8 5.5 104 1.6 1019 = 7.0 1015 C; 4 (c) the variation of pd across the collection area is a "map" of the image of the object on the collection area; each pd can be converted to a digital signal; these digital signals can be converted to an image on an LCD/screen; 2 [11]

Charge coupled device (CCD) (a) A digital camera is used to take a photograph of a plant. The CCD in the camera has 1.6 107 square pixels. Each pixel has an area of 2.3 10-10 m2. A particular leaf of the plant has an area of 2.5 10-2 m2. The image of the leaf formed on the CCD is 1.0 10-3 m2. Two indentations on the leaf are separated by 0.50 mm. Deduce that it is unlikely that the images of the two indentations will be resolved. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (4) (b) Light is incident on the image collection area for a time of 100 ms. The number of photons incident on one pixel is 5.5 104. Each pixel has a quantum efficiency of 80 and a capacitance 40 pF. (i) State what is meant by quantum efficiency. ......................................................................................................................... ......................................................................................................................... (1) (ii) Estimate the change in potential difference across each pixel. ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... (4) (c) Outline how the variation in potential difference across individual pixels enables a black and white image to be produced by a digital camera. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (2) (Total 11 marks)

B

Data are stored on an audio compact disc (CD) at a rate of f samples per second. Each sample contains b bits. A total of N bits are stored on the CD. Which of the following is the playing time of the CD in seconds?

(a) represents the smallest decimal number ie 20 of each of the bits / OWTTE; 1 (b) 0100: 4; 0101: 5; 1 Need both to receive the mark. (c) 20 characters = 160 bits; 1 Allow candidates to make assumptions regarding end of line character or equivalent but do not award mark for those that forget spaces or punctuation mark. (d) recognition that analogue format means paper/microfiche, etc.; accurate reproducibility of analogue form is difficult; (because of) susceptibility to noise (eg repeated photocopying); analogue format could be bulky; any other sensible comment/example; 5 (e) using up natural resources eg trees / large waste / waste disposal / OWTTE; 1 [9]

In a computer code, text (letters, spaces and punctuation marks) is represented by binary numbers. The letter "E" is represented by the two four bit binary numbers below. 0100 and 0101 (a) Define least significant bit. ................................................................................................................................... ................................................................................................................................... (1) (b) Calculate the decimal equivalent for the two four bit binary numbers. 0100 ......................................................................................................................... 0101 ......................................................................................................................... (1) (c) Using this computer code state how many separate bits would be needed to represent the following phrase. IBO Physics is easy! ................................................................................................................................... (1) (d) Discuss, in terms of reproducibilty and portability, the disadvantages of storing text in analogue rather than digital form. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (5) (e) State one environmental implication of storing text in analogue form. ................................................................................................................................... ................................................................................................................................... (1) (Total 9 marks)

C

In binary, the decimal number 20 is represented as A. 11101 B. 11000 C. 10100 D. 00010 (Total 1 mark)

A

Increasing the quantum efficiency of a CCD will increase the A. signal strength. B. magnification. C. pixel size. D. resolution.

D

Laser light of wavelength 500 nm is used to read the information on a CD. The approximate depth for a pit on the CD is A. 1000 nm. B. 500 nm. C. 250 nm. D. 125 nm.

A

Light incident on a pixel element in a charge-coupled device (CCD) produces electron-hole pairs. This is due to A. the photoelectric effect. B. a temperature gradient in the semiconductor lattice. C. electrodes across the surface of the pixel element. D. a chemical reaction on the oxide insulator.

B

Light incident on the pixel of a CCD causes electric charge to collect in the pixel. The amount of charge collected in a given time is proportional to which characteristic of the incident light? A. The degree of polarization B. The intensity C. The wavelength D. The frequency

C

N photons are incident on a pixel of a CCD. Each photon causes one electron of charge e to be emitted. The capacitance of the pixel is C. What is the resulting potential difference across the pixel? A. NeC B. C. D. (Total 1 mark)

A

The amount of charge that builds on a pixel in a charged coupled device (CCD) is proportional to which property of the incident light? A. Intensity B. Wavelength C. Frequency D. Amplitude

B

The capacitance of a pixel of a CCD is 3.2 pF. A pulse of light is incident on the pixel and as a result, 104 electrons are ejected from the pixel. The magnitude of the change in potential of the pixel is A. 5.0 × 10-16 V B. 5.0 × 10-4 V C. 2.0 × 103 V D. 2.0 × 1015 V

A

The depth of a "pit" on a CD is 150 nm. The wavelength of the laser used to read the information on the CD must be A. 600 nm. B. 450 nm. C. 300 nm. D. 150 nm.

(a) a circuit whose output (signal) is proportional, and opposite, to the input; 1 (b) (i) 8.0 108 A; 2 (ii) 80 mV; 1 (c) junction between resistors is at (about) 0 V / virtual earth; no current flows into op-amp / very high input resistance; very high gain;

The diagram below shows an inverting amplifier circuit. (a) State what is meant by an inverting amplifier circuit. ................................................................................................................................... (1) (b) The input voltage is 12 mV. Calculate (i) the current in the 150 k resistor. ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... (2) (ii) the potential difference between A and B. ......................................................................................................................... ......................................................................................................................... (1) (c) Outline any assumptions that you have made in (b). ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (2) (Total 6 marks)

C

The linear magnification of a digital camera is M. The length of one side of a pixel is l. A picture of two points of an object separated by a distance D is taken. The images of the points will be resolved on the CCD if the ratio is A. smaller than 1. B. equal to 1. C. equal to 2 or more. D. at least 10 or more. (Total 1 mark)

(a) (i) photoelectric effect; 1 (ii) the amount of charge/potential created in a pixel is proportional to the intensity of the incident light; the image is formed by registering the intensity of light in each pixel and the position of each pixel / OWTTE; 2 (b) number of photons in 15 ms = 3.6 × 10^6 × 15 × l0^-3 = 54 × 10^3; number of electrons emitted = 43 × 10^3; charge = 43 × 10^3 × 1.6 × l0^-19 = 69 × l0^-16 (C); V = (69 × 10^16 / 34 × 10^12 =) 0.20 mV; 4 (c) the retrieval speed is much faster; since each piece of data can be assigned an electronic address; data can be retrieved with less corruption / data less likely to be mis-read (on retrieval); some comparison with an analogue storage system e.g. book/ library/video tape; 3 max To award [3 max] the first and the third marking point must be addressed. [10]

This question is about CCDs and digital data storage. (a) An object is to be photographed using a digital camera. (i) State the name of the phenomenon in which light causes electrons to be emitted from a pixel of a CCD. ........................................................................................................................... (1) (ii) Outline how the image of the object on the CCD is formed. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (b) Photons are incident on one of the pixels of the CCD at a rate of 3.6 × 106 s-1. The pixel has capacitance 34 pF and quantum efficiency of 80 %. Determine the potential difference across the pixel after an exposure time of 15 ms. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (c) Outline, with reference to the retrieval of stored data, why it is better to store data in digital form rather than analogue form. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (Total 10 marks)

(a) the ratio of charge to potential difference/voltage; 1 (b) (i) number of photons per unit area per second = = 2.6 × 1015; number of photons per second on pixel = 2.6 × 1015 × 5.5 × 10-10; = 1.4 × 106 s-1 2 (ii) charge emitted per second = (1.4 × 106 × 1.6 × 10-19 =) 2.3 × 10-13 (C) pd per second = (V =) ; = 0.1 (V); time to reach 40 µV = 0.40 m s; 4 (iii) the quantum efficiency is unity (1)/100 % / each incident photon ejects an electron from the pixel; 1 [8]

This question is about CCDs. (a) Define capacitance. ...................................................................................................................................... ...................................................................................................................................... (1) (b) Light of a particular frequency and intensity 1.2 mW m-2 is reflected from an object on to a pixel of a CCD. The area of the pixel is 5.5 × 10-10 m2 and its capacitance is 2.2 pF. The energy of a photon of the light is 4.6 × 10-19 J. (i) Deduce that the rate at which photons are incident on the pixel is 1.4 × 106 s-1. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Using the answer to (b)(i), determine the time it takes the potential across the pixel to change by 40 µV. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (4) (iii) State one assumption that you have made in arriving at your answer in (b)(ii). ........................................................................................................................... ........................................................................................................................... (1) (Total 8 marks)

(a) (i) 1011; 1 (ii) as a series of bumps/pits and flats on the surface; a flat/bump corresponds to binary zero / transition between flat and bump is one; (vice versa) 2 (iii) light rays from the edge of the bump and the flat interfere; they will cancel out if the path difference between them is half a wavelength; 2 (b) (i) ratio of the charge stored in the pixel to the potential difference across the pixel; 1 (ii) number on photons per pixel = (4.0 × 10^13 ×2.8 × 10^-10 =) 1.12 × 10^4; number of electron(-hole pairs) = (1.12 × 10^4 ×0.74 =) 8.29 × 10^3; charge produced = (8.29 × 10^3 × 1.6 × 10^-19 =) 1.33 × 10^-15 (C); potential = (Q/C = 1.33 x 10^15 / 2.0 x 10^-11 =) 0.066 mV or 6.6 × 10-5 V; 4 [10]

This question is about CDs and CCDs. (a) Analogue signals are stored on a CD as a digital, binary signal. For an analogue signal of strength 11 V, (i) state the magnitude of the signal strength as a binary number. ........................................................................................................................... (1) (ii) describe how a digital signal, such as that in (a)(i), is stored on the CD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iii) outline how the stored digit one (1) in a digital signal is read from the CD using laser light reflected from the surface of the CD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (b) Unlike a CD, a CCD stores light incident on its surface in a digital form by dividing the surface into a large number of pixels. Each pixel has a fixed value of capacitance. (i) Define what is meant by the capacitance of a pixel. ........................................................................................................................... ........................................................................................................................... (1) (ii) Pixels of a particular CCD have an area of 2.8 × 10^-10 m^2 and a capacitance of 20 pF. A beam of monochromatic light is incident on the CCD. The number of photons per square metre arriving at the CCD is 4.0 × 10^13. The quantum efficiency of a pixel is 74 %. Determine the increase in potential difference across a pixel as a result of the incident light. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (4) (Total 10 marks)

(a) the ratio of charge to potential difference / C = (with terms defined); 1 (b) photons (in the light) create electron-hole pairs (in the pixel); these migrate to electrodes and so from C = there will be a p.d. cross the pixel / OWTTE; 2 (c) number of electron-hole pairs produced (= 0.75 × 1.2 × 104) = 9.0 × 103; charge produced (= 9.0 × 103 × 1.6 × 10-19) = 1.44 × 10-15 C; = 0.065mV; 3 [6]

This question is about capacitance and charge-coupled devices (CCD). (a) Define capacitance. ...................................................................................................................................... ...................................................................................................................................... (1) (b) Outline how light that is incident on a pixel on the surface of a CCD can produce a potential difference across the pixel. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (c) The number of photons incident on one pixel of a CCD for a certain period of time is 1.2 × 104. The capacitance of the pixel is 22 pF and the quantum efficiency is 75 %. Determine the change in potential difference across the pixel. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (Total 6 marks)

(a) images must be at least two pixels apart / OWTTE; 1 (b) (i) area of CCD = 3.8 × 10-4 m2; size of pixel = ; = 6.1 × 10-6 m 2 (ii) number of photons = 1.6 × 108 × 0.8 = 1.28 × 108; charge = 1.28 × 108 × 1.6 × 10-19 × 0.012 = 2.5 × 10-13; V = 7.0mV; 3 (iii) separation on CCD = 2.5 × 2.2 × 10-6 = 5.5 μm; this is less than pixel size / 6 μm so not resolved; 2 (c) higher retrieval speed; more portable; more reproducible; easily manipulated; 2 max Do not award marks for references to quality. [10]

This question is about charge-coupled devices (CCD). (a) State the condition necessary for two points on an image to be resolved by a CCD. ...................................................................................................................................... ...................................................................................................................................... (1) (b) The following data are for a CCD in a camera. Dimensions of CCD = 24 mm × 16 mm Number of pixels = 10.2 × 106 (i) Each pixel on the CCD is square and they all have the same dimensions. Show that the length of one side of a pixel is about 6 μm. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) The pixels have quantum efficiency of 80 % and a capacitance of 35 pF. Photons are incident on a pixel at a rate of 1.6 × 108 s-1. Calculate the potential difference across a pixel after 12 ms. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (iii) A photograph is taken of a distant building using the camera. The magnification of the CCD is 2.2 × 10-6. Two windows on the building are separated by 2.5 m. Determine whether the images of the windows can be resolved by the CCD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (c) In terms of data storage, state two advantages of using a digital camera as compared to an analogue camera that uses film. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 10 marks)

(a) small area on silicon/semiconductor chip/semiconductor lattice; that is the smallest part of the chip that can detect a photon / that behaves as a capacitor / OWTTE; 2 (b) photons cause emission of electrons/holes; this changes the potential difference (developed across the pixel); potential difference is proportional to light intensity; 3 (c) position of pixel/colour/wavelength; 1 (d) e.g. much greater quantum efficiency; sensitive to wider range of e.m. spectrum; processing time of image very much shorter; image can be processed easily / no need for image to be developed; image data can be transmitted directly; much less storage space needed; digital material can be re-used unlike film; film degrades with time; film experiences reciprocity failure; 2 max [8]

This question is about charge-coupled devices (CCD). (a) With reference to a CCD, state what is meant by a pixel. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) Outline how light falling on a CCD leads to an electrical signal being produced by a pixel. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (c) State one other piece of information that needs to be collected, in addition to the electrical signal in (b), in order that an image may be formed. ...................................................................................................................................... ...................................................................................................................................... (1) (d) Suggest two advantages of a CCD in comparison with a photographic film for image production. 1 ................................................................................................................................... ...................................................................................................................................... 2 ................................................................................................................................... ...................................................................................................................................... (2) (Total 8 marks)

(a) the potential difference is proportional to the intensity of light; the position of each pixel is recorded forming an image/an intensity map / OWTTE; 2 (b) (i) the ratio of the number of emitted electrons to the number of incident photons; 1 (ii) energy supplied is 1.4 × 22 × 10-6 × 85 × 10-3 =2.62 × 10-6 J; number is = 7.3 × l012; number per pixel is ; i.e. 1.5 × l06 3 (iii) electric charge created is 0.75 × 1.5 × 106 × 1.6 × 10-19 = 1.8 × 10-13 C; voltage is V = ; i.e. 15 mV 2 (iv) 15 = 8 + 4 + 2 + 1 = 1111; 1 (c) it gives the patient less exposure to X-rays (because a high quantum efficiency detector means the image would be formed quickly); 1 [10]

This question is about charge-coupled devices (CCDs). (a) Light from an object that is incident on the pixels of a CCD gives rise to potential differences across the pixels. Outline how these potential differences are used to produce an image of the object. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (b) The CCD of a particular digital camera has 5.0 × 106 pixels and a collecting area of 22 mm2. Light of intensity 1.4 W m-2 is incident on the collecting area of the CCD for a time of 85 ms. The average energy of the photons of the incident light is 3.6 × 10-19 J. The quantum efficiency of the CCD is 75 %. (i) State what is meant by quantum efficiency. ........................................................................................................................... ........................................................................................................................... (1) (ii) Show that the number of photons incident on one pixel of the CCD in the time interval of 85 ms is approximately 1.5 × 106. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (iii) The capacitance of a pixel of the CCD is 12 pF. Show that the potential difference established across the pixel is approximately 15 mV. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iv) The voltage in (b)(iii) is digitized into a four bit binary number. Determine the binary equivalent of this voltage. ........................................................................................................................... ........................................................................................................................... (1) (c) CCDs detecting X-rays are now used in medical diagnosis. State the advantage to the patient of an X-ray CCD detector with high quantum efficiency. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (1) (Total 10 marks)

(a) bit: a binary digit; either 0 or 1; least significant bit: determines whether a binary number is an odd or an even decimal number / determines the unit value of the decimal value of a binary number; it is the most right-hand digit of a binary number; 3 max (b) (i) 0; 1 (ii) (it is) encoded onto aluminium/metal surface of the CD as a series of "bumps/pits" and flats; the edge of a bump/pit represents binary 1, the flats between edges represent binary 0; 2 or reflection / no reflection from surface features; that results in binary digits 1 or 0; (c) vast numbers of CDs and DVDs are produced; hence, problem of disposal as they are not biodegradable / manufacture produces greenhouse gases / toxic material involved in their manufacture; Accept any other suitable alternative. 2 [8]

This question is about data storage. (a) With reference to binary numbers, define the term bit and explain what is meant by least significant bit. Bit: ...................................................................................................................................... ...................................................................................................................................... Least significant bit: ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (b) An acoustic signal is converted into an analogue voltage signal. The analogue signal is then converted to a digital signal. The maximum value of the voltage signal is 20 V. (i) State the value of the least significant bit of the binary number that represents the number 20. ........................................................................................................................... (1) (ii) Outline how the analogue signal after conversion to a digital signal may be stored on a compact disc (CD). ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (c) Suggest one implication that the storage of information in digital form on a CD may have in connection with environmental issues. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 8 marks)

(a) mention of pits; (allow bumps/flats/islands etc.)(*) laser/coherent light used(*); light is monochromatic(*); pits are 1/4 wavelength deep(*); mention of constructive/destructive interference; 4 max (*)These points can be awarded to a labelled diagram. (b) more layers of pits on the Blu-ray disk possible (because pits now shallower); the wavelength is smaller therefore higher resolution; track separation can be smaller(*); pit spacing can be smaller(*); more information can be stored; 4 max (*)Allow "track smaller" [1] as substitute for both marking points. [8]

This question is about digital data storage. (a) Describe, with reference to the structure of a DVD, how stored digital data are read. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (b) The Blu-ray storage system uses a laser diode that emits a wavelength of 405 nm, whereas the older DVD system uses radiation of wavelength 650 nm. Explain the advantages of using a smaller wavelength. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (Total 8 marks)

(a) (i) 25 = 16 + 8 + 0 + 0 + 1 ; = 11001; 2 (ii) accuracy-each letter/symbol can be assigned a specific binary number/byte; reproducibility-data can be retrieved many times without it becoming corrupted / OWTTE; storage/portability-much less space required to store a great deal of data/e.g. a large amount of data can be stored on a CD/DVD which is easily carried around / OWTTE; retrieval speed-some comparison e.g. internet with library; 2 max (b) the pits and bumps / bits of information (on a DVD) are much closer together (than on a CD) / multi-layered data storage; 1 (c) length of image (on CCD); length of object; 2 (d) length of image of CD =(2.0 × 10^-3 × 1.4 × 10^-2) = 2.8 × 10^-5(m); minimum length of pixel = 1.4 × 10^-5 (m); minimum number of pixels = ; = 2.0 × 10^6 or 2.1 × 10^6; (accept 4.0 × 10^6) 4 [11]

This question is about digital storage devices. (a) (i) Convert the decimal number 25 to binary. ........................................................................................................................... ........................................................................................................................... (2) (ii) Outline two advantages of storing a text in digital form rather than in analogue form. 1. ....................................................................................................................... ........................................................................................................................... 2. ....................................................................................................................... ........................................................................................................................... (2) (b) State, with reference to their structure, why more data can be stored on a DVD than on a CD. ...................................................................................................................................... ...................................................................................................................................... (1) (c) Define the term magnification as it applies to a CCD. ...................................................................................................................................... ...................................................................................................................................... (2) (d) A digital camera is used to photograph a particular object. Two small marks on the object are separated by a distance of 2.0 × 10-3 m. The camera has a magnification of 1.4 × 10-2 and an image collection area of 4.0 × 10-4 m2. Determine the minimum number of pixels that the CCD of a digital camera must have, in order that the images of the two marks on the object are just resolved. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (Total 11 marks)

(a) (i) very high/infinite open loop gain; very high/infinite input resistance; 2 (ii) -10; 1 (b) (i) potential across R2 = (10 + 2 =) 12 = 150I; (to give I = 0.08mA) 1 (ii) potential across R1 = Vin - 2.0 = IR1; Vin = 0.08 × 47 + 2.0; (= 5.8V) 2

This question is about operational amplifiers. (a) The diagram shows a circuit that uses an operational amplifier as an inverting amplifier. The point P is a virtual earth, that is at the same potential (0 V) as the earth line. (i) State the two properties of the operational amplifier which make P a virtual earth. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) In the circuit Rf = 100 kΩ and Rin = 10 kΩ. Calculate the gain of the amplifier. ........................................................................................................................... ........................................................................................................................... (1) (b) The diagram shows a circuit that uses an operational amplifier as a non-inverting Schmitt trigger. In the situation shown, the potential at point X is 2.0 V and the output potential Vout is at its minimum value of -10 V. Show that for the output potential to switch to its maximum value of +10 V (i) the current in the resistors R1 and R2 is 0.08 mA. ........................................................................................................................... ........................................................................................................................... (1) (ii) Vin must rise to 5.8 V. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 6 marks)

(a) d = π/4; rays reflected from land and pit interfere; path difference is 2d; destructive interference takes place if path difference is π/2 ; 4 (b) d = (640/4 =) 160nm 1 (c) (i) number of pits = (5 x 10^3 / 2x1900x10^9); = 1.32 × 109 number of bits = 4 × 1.32 × 10^9 (= 5.3 × 10^9); ≈ 5 × 10^9 2 (ii) 5 × 10^9 = 44.1 × 10^3 × 2 × 16 × t; t = ( (5x10^9 / 44.1 x 2 x 16) = 3.5 x 10^3 s =) 59min ≈ 60min; 2 (d) easier to transport; takes up less space; less noise/distortion during playback; play stored items in any order; less liable to damage; 1 max [10]

This question is about the compact disc (CD). The diagram shows light from a laser that is incident on a CD. (IMAGE) The reflected light is used to read the data stored on the CD. The depth of the pits is d and the wavelength of the light is λ. (a) Explain the relationship between λ and d that allows the laser beam to detect the edge of a pit. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (b) The wavelength of the laser light is 640 nm. Calculate the pit depth d. ...................................................................................................................................... ...................................................................................................................................... (1) (c) The diagram shows a series of pits on one part of the spiral track of an audio CD. The average length of one pit and the average length of one land are both 1900 nm. (IMAGE) Information is stored on the CD with a sampling frequency of 44.1 kHz. Each sample consists of two 16 bit binary numbers. (i) The total length of the spiral on the CD is approximately 5 km. On average the number of bits stored on a CD is equal to four times the number of pits. Show that the storage capacity of this CD is approximately 5 × 109 bits. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Using the answer to (c)(i) calculate the playing time of this audio CD. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (d) Describe one advantage, other than amount of data, of storing music on a CD rather than on a vinyl LP record. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (1) (Total 10 marks)

base stations: [2 max] located at the centre of a cell receiving and transmitting radio signals from and to mobile phones; communicates with the cellular exchange; selects from the frequencies allotted to it by the cellular exchange for a particular call; cellular exchange: [2 max] allows entry into the fixed telephone network; allocates different frequencies to base stations; in order to avoid interference between different calls; reroutes calls to different base stations when a mobile phone leaves one cell area and enters another; 4 max [4

This question is about the mobile phone system. In the mobile phone system, a particular geographic area is divided into a number of cells with a base station in each cell, each connected to a cellular exchange. Describe the function of the base stations and the cellular exchange. Base stations: ......................................................................................................................... ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ Cellular exchange: ................................................................................................................. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (Total 4 marks)

(a) the sign of the output voltage is the same as that of the input voltage; 1 (b) (i) G = (1+(90/10)=)10; 1 (ii) Vout (= GVin = 10 × 2.0) = 20 mV ; 1 (c) op-amp has a high input resistance and so takes little current; (open loop) gain is very large so potential difference between non-inv input and inv input is (effectively) zero; i.e. Vout = Vin; so G = 1 3 (d) (i) 3.0 V; 1 (ii) the resistance between A and B is smaller than 2 MΩ / the voltmeter draws current; 1 (iii) the voltmeter reads the output voltage of the amplifier and the input voltage is the potential difference to be measured; the two are equal since the gain is 1; 2

This question is about the operational amplifier. Diagram 1 shows a non-inverting amplifier circuit. Diagram 1 (a) Suggest why the amplifier is referred to as non-inverting. ...................................................................................................................................... ...................................................................................................................................... (1) (b) The input voltage for the amplifier in (a) is Vin = 2.0 mV. Calculate (i) the gain G of the amplifier. ........................................................................................................................... (1) (ii) the output voltage Vout. ........................................................................................................................... (1) (c) Diagram 2 shows a particular non-inverting amplifier. Diagram 2 Explain, in terms of the properties of an op-amp, why the gain of this non-inverting amplifier is equal to 1. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) (d) Diagram 3 shows a circuit in which the battery has an emf of 6.0 V and negligible internal resistance. Two 2.0 MΩ resistors are connected in series to the battery. Diagram 3 (i) State the value of the potential difference between points A and B. ........................................................................................................................... (1) (ii) A voltmeter of resistance 100 kΩ is used to measure the potential difference across points A and B. State why the reading on the voltmeter is not equal to the value stated in (d)(i). ........................................................................................................................... ........................................................................................................................... (1) (iii) The circuit in diagram 3 is modified to include the circuit shown in diagram 2. Diagram 4 Explain why the voltmeter reads the value of the potential difference as stated in (d)(i). ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 10 marks)

(a) linear as shown; saturation shown; 2 (b) (i) 0 V; 1 (ii) when the temperature rises above 50°C the resistance of the thermistor falls below R; and so the voltage at the non-inverting input of the op-amp is negative; (the output voltage then saturates at -12 V) giving the required potential difference for the buzzer to sound; 3 [6]

This question is about the operational amplifier. (a) On the axes below draw a sketch graph to show the variation with input voltage Vin of the output voltage Vout of a non-inverting operational amplifier. (IMAGE) (2) (b) A temperature warning device makes use of a buzzer that sounds when the potential difference across it is 24 V. The circuit in the warning device is shown. (IMAGE) It is required that the buzzer should sound when the temperature of the thermistor rises above 50 °C. (i) State the voltage at point Q. ........................................................................................................................... (1) (ii) At a temperature of 50 °C the resistance of the thermistor is R. Explain why the buzzer will sound when the temperature rises above 50 °C. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (Total 6 marks)

B

To retrieve information stored on a CD, light of wavelength 800 nm is used. To retrieve information stored on a DVD, light of wavelength 400 nm is used. Which of the following gives the ratio ? A. 8 B. 2 C. 1 D. 0.5 (Total 1 mark)

B

Which of the following ratios is the definition of quantum efficiency of a pixel?