Pre Board Exam ELECS
1.51 T
A closed magnetic circuit of cast steel contains a 6 cm long path of cross-sectional area 1 cm² and a 2 cm path of cross-sectional area 0.5 cm². A coil of 200 turns is wound around the 6 cm length of the circuit and a current of 0.4 A flows. Determine the flux density in the 2 cm path, if the relative permeability of the cast steel is 750.
1/3
A silicon sample A is doped with 10¹⁸ atoms/cm³of boron. Another sample B of identical dimensions is doped with 10¹⁸ atoms/cm³ of phosphorus. The ratio of electron to hole mobility is 3. What is the ratio of conductivity of the sample A to B?
the product of B and I
According to Hall effect, the Hall voltage is proportional to _______. Note: B is the magnetic field and I is the current.
De Morgan`s theorem
According to one of the theorems of Boolean algebra, a NAND gate is equivalent to a bubbled OR gate and a NOR gate is equivalent to a bubbled AND gate. What is this theorem?
depends upon the temperature of the semiconductor
According to the Einstein relation, for any semiconductor the ratio of diffusion constant to mobility of carriers:
every time the probe is used with a different oscilloscope
An oscilloscope probe must be compensated:
long propagation delay and low power consumption
As a general rule, the lower the value of the speed-power product, the better the device because of its:
70 deg Celsius
At what ambient temperature do resistors are rated for maximum wattage?
1A
Consider an arbitrary number system with independent digits as 0, 1 and A. What would be the sixth number in this number system?
Both are correct
Consider the following statements:S1: Current gain of an amplifier is independent of the input and the load impedancesS2: BJT's h_fe is most sensitive to changes in the collector current and h_oe is the least sensitive to changes in the collector current
P₁ < P₂
Consider two energy levels: E₁, E eV above the Fermi level, and E₂, E eV below the Fermi level. P₁ and P₂ are, respectively, the probabilities of E₁ being occupied by an electron and E₂ being empty. Then
exhibit short carrier life time and are used for fabricating lasers
Direct band gap semiconductors _____.
both the electric field and the carrier concentration
Drift current in semiconductors depends upon:
n-channel depletion
Electron conduction in an n-channel depletion type MOSFET is associated with:
n-channel enhancement
Electron conduction in an n-channel enhancement MOSFET is associated with:
series resonant circuit with the first choke and first capacitor
Excessive rectifier peak current and abnormally high peak inverse voltages can be caused in a power supply by the filter forming a:
-114
Find the decimal equivalent of a binary number 10001110, which has been represented in 2's complement form.
12%
For a 1/8 watt resistor, what is the maximum allowable change in resistance for a 1000-hour rated load life test?
greater, larger
For a certain magnetic material, the ______ the area inside the hysteresis loop, the _____ the hysteresis losses.
5.2 Ω
For a common-base BJT configuration having Ie = 5 mA and α = 0.97, an AC signal of 5 mV is applied between the base and the emitter terminals. What is the input impedance?
double that of the full-wave center-tap rectifier
For a given transformer the maximum output voltage available from a full-wave bridge rectifier circuit will be:
49 mA
For an NPN transistor connected as shown in the following figure, V_BE = 0.7 V. Given that reverse saturation current of the junction at room temperature 300 K is 10¯¹³ A, what is the emitter current (h =1)?
none of the choices
For the following statements, choose the correct answer.S1: The amplification factor (h_fe) is most sensitive to changes in collector current, whereas output impedance parameter is least sensitive. S2: Current gain of an amplifier is independent of the input impedance of the amplifier and the applied load.
By increasing the horizontal sweep rate and the vertical amplifier frequency response
How can the frequency response of an oscilloscope be improved?
By adding resistance in parallel with the meter
How can the range of an ammeter be increased?
Less power dissipation and slower speed
How does the 4000 series of CMOS logic compare in terms of speed and power dissipation to the standard family of TTL logic?
A feedback connection to an error amplifier is made directly to the load
How is remote sensing accomplished in a linear voltage regulator?
1
If f(A+ B+ C+ D) were a Boolean function, then f(A+ B+ C+ D) + f´(A+ B+ C+ D) would be equal to _____.
a decrease in the threshold voltage
If fixed positive charges are present in the gate oxide of an N-Channel enhancement type MOSFET, it will lead to:
It is equivalent to a pure resistance
If you plot the impedance of a circuit using the rectangular coordinate system and find the impedance point falls on the right side of the graph on the horizontal axis, what do you know about the circuit?
2.8
In a full-wave center-tap power supply, regardless of load conditions, the peak inverse voltage (PIV) will be _____ times the RMS voltage:
To equalize voltage drops and guard against transient voltage spikes
In a high voltage power supply, why should a resistor and capacitor be wired in parallel with the power-supply rectifier diodes?
temperature of the semiconductor
In an intrinsic semiconductor, the free-electron concentration depends on:
voltage-current feedback
In the AC equivalent circuit shown in the figure, if i_in is the input current and R_F is very large, the type of feedback is:
479 mV
In the circuit shown below, the input offset voltage and the input offset current are V_io = 4 mV and I_io = 150 nA. Calculate the total offset voltage.
Emitter Load
In the figure shown below, what is the purpose of R?
At microwave frequencies
In what application is gallium-arsenide used as a semiconductor material in preference to germanium or silicon?
Common-Base Configuration
In which of the following transistor configurations, is the input impedance least dependent on the load resistance?
Schmitt gates
Logic gates with associated hysteresis are called ______.
14 and 16
Number of bits required to encode the decimal numbers from 0 to 9999 in straight binary and BCD codes would be, respectively, ______.
Because it has both the voltage gain and cur-rent gain greater than unity.
Power gain is maximum in CE configuration whereas it does not have the maximum voltage gain nor the maximum current gain. Why?
3
The Boolean function Y= AB+ CD is to be realized using only two-input NAND gates. What is the minimum number of gates required?
Complementation Theorem
The Quine−McCluskey tabulation method of simplification of Boolean functions is based on:
A higher terminal voltage output
The advantage of the capacitor input filter over the choke input filter is:
inversely proportional to the doping concentration
The concentration of minority carriers in an extrinsic semiconductor under equilibrium is:
reads accurately only when the attenuator is properly terminated
The dial calibration on the output attenuator of a signal generator:
picojoules
The figure-of-merit of a logic family is often measured in the units of ______.
RC network only
The first and the last critical frequencies (singularities) of a driving point impedance function of a passive network having two kinds of elements, are a pole and a zero respectively. The above property will be satisfied by:
Small signal operational at low frequency
The h-parameter equivalent circuit of a BJT is valid for:
Thevenin's equivalent circuit at the input and Norton's equivalent circuit at the output
The hybrid equivalent circuit of a transistor has:
Z₁₁ = 2.75 Ω and Z₁₂ = 0.25 Ω
The impedance parameters Z₁₁ and Z₁₂ of the two-port network shown in the following figure are:
boron
The impurity commonly used for realizing the base region of a silicon N-P-N transistor is ______.
15.082(cos4000πt) µV
The input to an op-amp differentiator circuit is a sinusoidal voltage of peak value 10 µV and frequency of 2 kHz. If the values of differentiating components are given as R = 40 kΩ and C = 3 µF, determine the output voltage.
improve voltage regulation
The main function of the bleeder resistor in a power supply is to provide a discharge path for the capacitor in the power supply. But it may also be used for a secondary function, which is to:
taking the slope of the output characteristic curve at the operating point
The parameter h_oe can be determined by:
Less
The power-handling capability of most Zener diodes is rated at 25 degrees C or approximately room temperature. If the temperature is increased, the power handling capability is:
The abundance of silicon on the surface of the Earth
The primary reason for the widespread use of Silicon in semiconductor device technology is:
False
The resistivity of the semiconductor is of the order of 10¯³ Ω⋅cm.
diffusion current
Under low-level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially the ______.
When it is gated on
Under what operating condition does a silicon-controlled rectifier (SCR) exhibit electrical characteristic similar to a forward biased silicon rectifier?
100
Use the table provided in the figure of collector characteristics to calculate βac at V_CE = 15 V and I_B = 30 µA.
High gain, high input impedance and low output impedance
What are the advantages of a Darlington pair audio amplifier?
Op-amps exhibit gain rather than insertion loss
What are the advantages of using an op-amp instead of LC elements in an audio filter?
Op-amp circuits are used as audio filters for receivers
What are the principal uses of an op-amp RC active filter in amateur circuitry?
Peak inverse voltage; average forward current
What are the two major ratings that must not be exceeded for silicon-diode rectifiers used in power-supply circuits?
The input impedance is essentially determined by the gate biasing network
What determines the input impedance of a FET common-source amplifier?
The output impedance is essentially determined by the drain resistor
What determines the output impedance of a FET common-source amplifier?
It gives an indication of the resonant frequency of a circuit
What does a dip meter do?
Time base accuracy, speed of the logic, and time base stability
What factors limit the accuracy, frequency response and stability of a frequency counter?
Accuracy of the time base and the linearity and bandwidth of the deflection amplifiers
What factors limit the accuracy, frequency response and stability of an oscilloscope?
Resistance is added in series with the meter
What happens inside a multimeter when you switch it from a lower to a higher voltage range?
As VHF and UHF mixers and detectors
What is a common use for the hot-carrier (Schottky) diode?
A high-gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally
What is an operational amplifier (op-amp)?
The conduction of a control element is varied in direct proportion to the line voltage or load current
What is one characteristic of a linear electronic voltage regulator?
Field
What is part of a database that holds only one type of information?
0.718 eV
What is the band gap energy of Germanium at 300k
The AC voltage causing the same heating of a given resistor as a DC voltage of the same value
What is the equivalent to the RMS value of an AC voltage?
50 Ω
What is the impedance looking into nodes 1 and 2 in the given circuit?
It allows ripple in the passband in return for steeper skirts
What is the primary advantage of the Chebyshev filter over the Butterworth filter?
It provides a constant minimum load for Q1
What is the purpose of R2 in the circuit shown below?
1+βA
What is the ratio of the input impedance with series feedback to that without feedback?
16580
What is the reluctance of a piece of mumetal of length 150 mm and cross sectional area 1800 mm^2 when the relative permeability is 4000
A Series Regulator
What type of linear regulator is used in applications requiring efficient utilization of the primary power source?
A three-terminal regulator
What type of voltage regulator contains a voltage reference, error amplifier, sensing resistors and transistors, and a pass element in one package?
The junction diode
When a silicon-controlled rectifier (SCR) is triggered, to what other semiconductor diode are its electrical characteristics similar (as measured between its cathode and anode)?
a diagonal straight line
When using Lissajous figures to determine phase differences, an indication of zero or 180 degrees is represented on the screen of an oscilloscope by:
including a suitable bleeder resistance
When using a choke input filter, a minimum current should be drawn all the time when the device is switched on. This can be accomplished by:
Reactive component
When using rectangular coordinates to graph the impedance of a circuit, what does the vertical axis represent?
1.1%
Which of the following is not a standard-failure-rate levels per 1000 hours of resistors?
Both S1 and S2
Which of the following statements is/are true?S1: Conductivity of silicon is less than that of germanium at room temperature (300K).S2: As the temperature increases, the Fermi level of both N-type and P-type semiconductor materials moves towards the center of the forbidden energy band gap.
Which of these is a search engine?
Field effect transistor
Which semiconductor device has characteristics most similar to a triode vacuum tube?
They are susceptible to damage from static charges
Why are special precautions necessary in handling FET and CMOS devices?
The gate-protective Zener diode prevents the gate insulation from being punctured by small static charges or excessive voltages.
Why do many MOSFET devices have built-in gate protective Zener diodes?
Because of skin effect
Why is the resistance of a conductor different for RF currents than for direct currents?
000111
X= 01110 and Y= 11001 are two five-bit binary numbers represented in two's complement format. The sum of X and Y represented in two's complement format using 6 bits is ______.
utilizing a dual trace oscilloscope
You can use an oscilloscope to display the input and output of a circuit at the same time by:
A URL
https://www.excelreviewcenter.com.ph is an example of what?
