physics final
A 400 W computer (including its monitor) is turned on for 5.0 hours per day. If electricity costs 10 cents per kWh, how much does it cost to run the computer for a 30-day month?
$6
An object is placed 50 cm in front of a concave mirror with a focal length of 25 cm. What is the magnification produced by the mirror?
-1.0 (?)
A multiloop circuit is shown in the figure. Find the current I1 if the batteries are ideal.
-2 A
The distance between an object and its upright image is 9.0 cm. If the magnification is 0.25, what is the focal length of the lens being used to form the image?
-4.0 cm
A +5.0 microC charge is 60cm to the right of a -8.0microC charge. Determine the electric potential at the midpoint between the two charges.
-90 kV (V=kQ1/0.5r + kq2/0.5r)
Consider a series circuit in which the capacitive reactance equals the inductive reactance. What is the phase angle between current and voltage for this circuit?
0
The maximum torque on a flat current-carrying loop occurs when the angle between the plane of the loop's area and the magnetic field vector is
0
A charge of 12 C passes through an electroplating apparatus in 2.0 min. What is the average current in the apparatus?
0.10 A (I=Q/t)
A flat circular loop of wire is in a uniform magnetic field of 0.30 T. The diameter of the loop is 1.0 m, and a 2.0 A current flows in it. What is the magnitude of the magnetic torque on the loop when the plane of the loop is parallel to the magnetic field?
0.47 N*m (?)
The secondary coil of an ideal neon sign transformer provides 7500 V at 10 mA. The primary coil operates on 120 V. What current does the primary draw?
0.625 A (Np/Ns = Is/Ip)
The phase angle of an ac circuit is 49 degrees. What is the power factor?
0.66 (cos49)
Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. What are the signs of the charges of these three particles?
1 is negative, 2 is neutral, 3 is positive
A proton (m = 1.67 x 10^-27 kg) is suspended at rest in a uniform electric field near the surface of the Earth. Take into account the gravitational force and determine the magnitude and direction of the electric field.
1.0 x 10^-7 N/C vertically upward (E = mg/q)
A straight wire carries a current of 10 A at an angle of 53 degrees with respect to the direction of a uniform 0.30 T magnetic field. Find the magnetic force on a 0.50m length of the wire.
1.2 N (F=ILBsintheta)
Determine the maximum torque on an electric dipole (q=3.0nC and a separation distance of 8.0mm) placed in a uniform magnetic field of 5000 N/C.
1.2 x 10^-7 N*m (T = qlE)
The amplitude of the electric field for a certain type of electromagnetic wave is 600 N/C. What is the rms value of the magnetic field for that wave?
1.40 microT? (B=E/c... so it should be 2 microT but that's not what the scantron says)
Two identical spheres have the same electric charge. If their separation distance is doubled, the force each exerts on the other will be
1/4 as large
The power rating of a 400 Ohm resistor is 0.25 W. What is the maximum voltage you can safely connect across its ends?
10 V (P=V^2/R)
The coil of an ac generator has 50 loops and a cross-sectional area of 0.25m^2. What is the maximum emf that can be generated by this generator if it is spinning with an angular speed of 4.0 rad/s in a 2.0 T magnetic field?
100 V (E=NBwA)
Radiation of a single frequency reaches the upper atmosphere of the Earth with an intensity of 1370 W/m^2. What is the amplitude of the electric field associated with this radiation?
1020 V/m (?)
A camera flash unit stores energy in a 600microF capacitor at 200V. How much electric energy is stored in the device?
12 J (U=1/2CV^2)
What is the frequency of 20 mm wavelength microwaves?
15 GHz (c=lambda*f)
If the index of refraction of a material is 2, this means the light travels
2 times as fast in a vacuum as it does in the material
A proton travels at a speed of 5.0 x 10^7 m/s through a 1.0 T magnetic field. What is the magnitude of the magnetic force on the proton if the angle between the proton's velocity and the magnetic field vector is 30 degrees?
2.0 x 10^-14 N (F=qvBsintheta)
An electric device delivers a current of 3.2 A for 10 seconds. How many electrons flow through this device?
2.0 x 10^20 (I=Q/t)
A high power line carries a current of 1.0 kA. What is the strength of the magnetic field this line produces at the ground, 10 m away?
20 microT (uo/2pi x I/r)
A 120-V rms voltage at 1000 Hz is applied to a series RLC circuit with an equal value of inductive and capacitive reactance and a 200 Ohm resistance. What is the impedance of this circuit?
200 Ohms (Z = R)
Paper has a dielectric constant of 3.4 and a dielectric strength of 15 MV/m. Suppose that a typical sheet of paper has a thickness of 0.11 m and you make a "homemade" capacitor by placing a sheet of 30 cm x 20 cm paper between two aluminum sheets of the same size. What is the maximum amount of charge that can be placed on the aluminum plates before your capacitor breaks down?
27 micro C (C = keoA/d)
An ideal solenoid has a self-inductance L. If you now double its radius and its length, but do not change the number of coils, what will its self-inductance be?
2L
Blue light of wavelength λ passes through a single slit of width d and forms a diffraction pattern on a screen. If we replace the blue light by red light of wavelength 2λ, we can retain the original diffraction pattern if we change the slit width to
2d
A -8.0 D lens is head 25 cm from an object 10 cm high. Determine the height of the image.
3.3 cm, upright (?)
Three charged particles are arranged in a straight horizontal line, with Q1 (-8.0microC) on the left, Q2 (+3microC) in the middle, and Q3 (-4.0microC) on the right. If the distance between Q1 and Q2 is 2.6 m and the distance between Q2 and Q3 is 1.4 m, determine the magnitude and direction of the net electrostatic force on Q3.
3.6 N to the left
Estimate the average power output of the sun, given that about 1370 W/m^2 reaches the upper atmosphere of the Earth. The mean Earth-Sun distance is 149.6 x 10^6 km.
3.85 x 10^26 W (?)
What is the magnitude and direction of the electric force on an electron in a uniform electric field of strength 3000 N/C that points due east?
4.8 x 10^-16 N, west (=E x 1.6 x 10^-19)
A typical home may require a total of 2000 kWh of electrical energy per month. Suppose you would like to obtain this energy form sunlight, which has an average daylight intensity of 1000 W/m^2 . Assuming the sunlight is available 8 hr per day, 25 days per month (accounting for cloudy days), and that you have a way to store the energy from the solar collectors when the Sun isn't shining, determine the smallest collector area that will provide the needed energy, assuming a collector efficiency of 25% (i.e. the collector converts 25% of the available energy into usable energy).
40 m^2 (P=I/A)
A fiber optic material has an index of refraction of 1.5. What is its critical angle if it is in air?
42 degrees (sintheta = n2/n1)
A certain metal wire has a cross-sectional area of 1.0cm^2 and a resistivity of 1.7 x 10^-8 Ohm*m. How long would it have to be to have a resistance of 1.0 Ohms?
5.9 km (R = pl/A)
A 2.0 microF capacitor is charged to 10 V and then discharged through a 4.0 M-Ohm resistor. How long will it take for the voltage across the capacitor to drop to 3.7 V?
8.0 s (Vo = Vmax / e^t/RT)
An electron and proton are 5.0 x 10^-11 m apart. Determine their electric dipole moment when they are at rest.
8.0 x 10^-30 C*m (1.6 x 10^-19 x distance)
When two resistors, R1 and R2, are connected in series across a 10 V battery, the potential difference across R1 is 8.0 V. When R1 and R2 are connected in parallel to the same battery, the current through R2 is 0.50 A. Determine the resistance value of R1.
80 Ohms
An ideal solenoid is 3.0cm long with a cross-sectional area of 1.00 x 10^-4 m^2 and has 4000 turns of wire. If the coil carries a current of 5.0 A, how much energy is stored in its magnetic field?
840 mJ (B = uoNI/l --> U=0.5*AlB^2/uo)
A series ac circuit has a resistance of 4.0 Ohms, a capacitive reactance of 26 Ohms, and an inductive reactance of 17 Ohms. Find the impedance of the circuit.
9.8 Ohms (Z = sqrt(R^2 [Xl-Xc]^2))
A flat square coil of wire with 15 turns and an area of 0.40m^2 is placed with the plane of its area parallel to a magnetic field of 0.75 T. The coil is flipped so its plane is perpendicular to the magnetic field in a time of 0.050 s. What is the magnitude of the average induced emf in the coil?
90 V (E = NBAw)
Which of the following types of electromagnetic radiation travels the fastest in a vacuum?
All the above travel at the same speed
If unpolarized light is incident from the left on three polarizers as shown in (Figure 1), in which case will some light get through?
Case 2 only
Which vector best represents the direction of the electric field at the fourth corner of the square due to the three charges shown in the figure below? All three charges have the same magnitude.
D (the arrow pointing away from the corner)
One Coulomb, which is a unit of electric charge, is the magnitude of the charge on one electron.
False
Two protons separated by a distance d form an electric dipole.
False
Q1 = -0.10 microC is located at the origin. Q2 = +0.10 microC is located on the positive x-axis at x = 1.0m. Which of the following is true of the force on Q1 due to Q2?
It is attractive and directed in the +x direction.
Which of the following is NOT a correct expression for the speed of light?
None of the expressions are correct
When you double the voltage across a certain material or device, you observe the current increases by a factor of 3. What can you conclude?
Ohm's law is not obeyed.
Four unequal resistors are connected in a parallel with each other. Which one of the following statements is correct about this combination?
The equivalent resistance is less than that of the smallest resistor.
When glasses (or contact lenses) are used to correct nearsightedness, where should the corrective lens form an image of an object located at infinity in order for the eye to form a clear image of that object?
The lens should form the image at the far point.
When glasses (or contact lenses) are used to correct farsightedness, where should the corrective lens form an image of an object located between the eye and the near point in order for the eye to form a clear image of that object?
The lens should form the image at the near point.
Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and a radius 2b. Which statement about the resistance across the ends of the wires is true?
The resistance of wire #1 is twice as high as that of wire #2. (R = pL/pib^2)
An experiment is conducted in which red light is diffracted through a single slit. Listed below are alterations made, one at a time, to the original experiment, and the experiment is repeated. After each alteration, the experiment is returned to its original configuration. Which of these alterations decreases the angles at which the diffraction minima appear?
The slit width is doubled, a green light source is used, the experiment is conducted in a water-filled tank (sintheta = m*lambda/W)
If the entire apparatus were submerged in water, would the width of the central peak change?
The width would decrease
A double-slit experiment yields an interference pattern due to the path length difference from light traveling through one slit versus the other. Why does a single slit show a diffraction pattern?
There is a path length difference from waves originating at different parts of the slit.
A circular wire ring is situated above a long straight wire, as shown in the figure. The straight wire has a current I flowing to the right, and this current is increasing at a constant rate. Which of the following statements is true?
There is an induced current in the wire ring, directed in a clockwise orientation
Which one of the following statements is correct?
When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point in the direction of the magnetic field lines
If you hold two fingers very close together and look at a bright light, you see lines between the fingers. What is happening?
You are seeing a diffraction pattern.
For total internal reflection to take place, light must travel from
a medium of higher index of refraction to a medium of lower index of refraction
Light passes through a slit that is about 5×10−3 m high and 5×10−7 m wide. The central bright light visible on a distant screen will be
about 5×10−3 m high and wider than 5×10−7 m .
The unit kilowatt-hour is a measure of
an amount of energy
Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all other quantities remained the same, the magnetic field inside the solenoid will
become one-half as strong as initially
If the earth-sun distance were doubled, the intensity of radiation from the Sun that reaches the Earth's surface would
decrease to 1/4
When the current through a resistor is increased by a factor of 4, the power dissipated by the resistor
decreases by a factor of 16
The colors in a rainbow are caused by
different amounts of refraction for light of different colors by the water in the raindrops
The electron-volt is a unit of
energy
A 18 V battery is connected to a resistor with the following colored bands, reading from left to right: brown/black/orange, with a single gold band on the right end. The current flowing in the circuit will be
equal to, or near, 1.8 mA.
If the amplitudes of both the electric and magnetic fields of an electromagnetic wave triple in magnitude, how does the average intensity of the wave change?
increase by a factor of 9
A parallel-plate capacitor is charged to a charge Q and is then disconnected from a battery. The two plates are initially separated by a distance d. Suppose the plates are then pulled apart until the separation is 2d. The energy stored in the capacitor will
increase by a factor of two
If two oppositely charge parallel conducting plates are moved until they are half the original separation distance without changing the charge on either plate, the electric field near center between the plates would
increase by a factor of two
A transformer is a device used to
increase or decrease ac voltage
A lens can be characterized by its power, which
is the reciprocal of the focal length
A pure capacitor is connected to an ac power supply. In this circuit, the current
leads the voltage by 90 degrees
When capacitors are connected in series, the effective capacitance _____________ the smallest capacitance; when capacitors are connected in parallel, the equivalent capacitance is _____________ the largest capacitance.
less than; greater than
The Earth's magnetic field acts like a bar magnet with it's north pole
near, but not at the exact same location as, the north geographic pole
The direction of the force on a current-carrying wire in a magnetic field is
perpendicular to both the current and the magnetic field
In an electromagnetic wave in free space, the electric and magnetic fields are
perpendicular to one another and perpendicular to the direction of wave propagation
A flat coil is in a uniform magnetic field. The magnetic flux through the coil is greatest when the plane of its area is
perpendicular to the magnetic field
Which one of the following lists gives the correct order of the electromagnetic spectrum from low to high energy?
radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
Light passing through a double-slit arrangement is viewed on a distant screen. The interference pattern observed on the screen would have the widest spaced fringes for the case of
red light and small slit spacing
In an RLC ac circuit, the values of the inductance and capacitance are both doubled. As a result of this change, the resonance frequency of the circuit is
reduced to one-half the original value
An air filled capacitor (K~1) consisting of two parallel plates separated by a distance d is connected to a battery of constant voltage V and acquires a charge Q and then disconnected from the battery. Next, a slab of dielectric material with K=3 is inserted between the plates of the capacitor. The charge on the plates will
remain the same
A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitor of capacitance 2C is connected in series with the first one, the time constant of the new RC circuit will be
smaller than before
If the primary coil of a transformer contains more loops than the secondary coil then it is a
step-down transformer
When electric field lines are curved, the electric field vector at any point is ___________ to the field line at that point.
tangent
Two identical positive charges are placed near each other. At the point halfway between the two charges,
the electric field is zero and the potential is positive.
An object is placed at a distance 2f in front of a lens with a focal length equal to +f. Which of the statements listed above are true regarding the image?
the image is real, the image is inverted, the image height is the same as the object height, the image is located at 2f
An object is placed at a distance 6f in front of a lens with a focal length equal to +f. Which of the statements listed above are true regarding the image?
the image is real, the image is inverted, the image is diminished in size, the image is located between the focal point (f) and 2f
An object is placed at a distance of 1.5f in front of a mirror with a focal length equal to +f. Which of the statements above are true regarding the image?
the image is real, the image is inverted, the image is enlarged in size, the image is located at a point greater than 2f
An object is placed at a distance 3f in front of a lens with a focal length equal to -f. Which of the statements listed above are true regarding the image?
the image is virtual, the image is upright, the image is diminished in size, the image is located between the mirror (or lens) and the focal point
An object is placed at a distance 5f in front of a mirror with a focal length equal to -f. Which of the statements listed above are true regarding the image?
the image is virtual, the image is upright, the image is diminished in size, the image is located between the mirror (or lens) and the focal point
An object is placed between a mirror (with a positive focal length) and the focal point. Which of the statements above are true regarding the image?
the image is virtual, the image is upright, the image is enlarged in size
Kirchoff's junction rule is a statement of
the law of conservation of charge
Kirchhoff's loop rule is a statement of
the law of conservation of energy
The number of protons in the nucleus of an electrically neutral atom is equal to
the number of electrons surrounding the nucleus
Four charges of equal magnitude, but possibly different sign, are placed on the corners of a square. What arrangement of charges will produce an electric field with the greatest magnitude at the center of the square?
two positive and two negative
A hollow box made of conducting material is placed in a uniform electric field. The magnitude of the electric field inside the box will be
zero
