True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 100. The exam period was 90 minutes; the average score was 76.4; the median score was 78. Click here to see page1 page2 of the formula sheet that came with the exam.
A circuit made with a battery, a switch, an inductor. and three resistors is shown in the figure. To begin with, switch S has been open for a long time. Then at time t = 0 the switch is closed.
The initial current through the inductor immediately after the switch is closed is 0 A.
(T) True (F) False
(a) L = 0.19 mH (b) L = 0.56 mH (c) L = 0.96 mH (d) L = 1.93 mH (e) L = 2.89 mH
What is the direction of the current in the right hand loop containing L, R2 and R3 immediately after the switch is opened?
(a) clockwise (b) counterclockwise
(a) τ = L / R1 (b) τ = L / (R1+R2) (c) τ = L / (R1+R2+R3)
A circuit made up of a battery, a switch, an inductor, a capacitor and a resistor is shown in the figure below. After being closed for a long time, the switch S is opened at time t = 0.
Immediately after the switch is opened, what is the direction of the current through the capacitor?
(a) toward the top of the page (b) toward the bottom of the page (c) the current is 0
(a) 1.34 volts (b) 1.90 volts (c) 2.68 volts (d) 4.02 volts (e) 7.20 volts
(a) The current is initially 0 through the inductor so you don't have to wait at all. (b) 7.0 × 10-4 s (c) 1.4 × 10-3 s (d) 2.1 × 10-3 s (e) 2.8 × 10-3 s
A circular capacitor is hooked up to some external electronics that cause a constant current I to flow into it for a brief period of time. This problem studies what happens in the vicinity of the capacitor during that time period. The figures below shows a perspective and a side view of the capacitor and the wires coming in and out of it. The radius of the capacitor is R, the gap between the plates is d and R >> d. This means you can assume that the electric field in the capacitor is uniform and directed straight across the gap, although it may change with time. Three points, labeled 1, 2 and 3, are located a distance R/2 from the center line, with points 1 and 3 outside and point 2 inside the capacitor.
During the time interval that the constant current I is flowing through the capacitor, the magnetic field at point 2 is
(a) directed out of the page. (b) directed into the page.
(a) (b) (c) (d) (e)
This question and the next two refer to this situation:
A monochromatic laser beam is polarized in the x- direction and propagates in the positive z-direction along the z-axis as shown in the figure. It passes through an ideal quarter wave plate at the origin. The fast and slow axes are oriented at 45° relative to the x-axis. Then, at z = d the light beam passes through an ideal linear polarizer with the polarization direction tilted at 45° relative to the x-axis as shown in the figure.
The intensity of the beam after it passes through the quarter wave plate is
(a) equal to the incident intensity. (b) one half the incident intensity. (c) one quarter the incident intensity.
(a) Pave = 0.33 mW (b) Pave = 0.57 mW (c) Pave = 0.67 mW (d) Pave = 1.33 mW (e) Pave = 1.67 mW
(a) (b) (c)
(a) θ = 27.4° (b) θ = 41.8° (c) θ = 45.0° (d) θ = 53.1° (e) θ = 56.4°
Which expression correctly gives the magnetic field of this wave?
(a) I4 / I0 = 0.211 (b) I4 / I0 = 0.326 (c) I4 / I0 = 0.404 (d) I4 / I0 = 0.571 (e) I4 / I0 = 0.653
A series RLC circuit is driven by a sinusoidal voltage generator. It is shown in the figure below. The resistance is 200 Ω. The maximum voltage amplitude supplied by the voltage generator VG is 141 V. The voltage VR across the resistor is measured to be VR = 100 cos(1000πt) volts. The voltages measured across the resistor and the voltage generator as functions of time are also sketched below. In particular, it is found that the voltage across the generator lags the voltage across the resistor.
The frequency f produced by the generator is:
(a) 500 Hz (b) 1000 Hz (c) 1500 Hz (d) 250 Hz (e) 100 Hz
(a) positive. (b) negative. (c) zero.
(a) 100 W (b) 70.5 W (c) 50 W (d) 35.25 W (e) 25 W
A sinusoidal voltage generator drives a series RLC circuit as shown in the figure below.
As ω → 0, the generator voltage leads the current.
(a) The average power supplied by the generator always exceeds Irms2 R . (b) The average power supplied by the generator always equals Irms2 R . (c) The average power supplied by the generator is always less than Irms2 R .
A sinusoidal voltage generator drives a series RL circuit as shown in the figure below. The angular frequency of the generator is ω = 2000 rad/sec. The rms EMF supplied by the generator is 100 V and the rms current in the circuit is measured to be 2 A. The time-averaged power supplied by the generator is 120 W.
The resistance R is
(a) 60 Ω. (b) 30 Ω. (c) 120 Ω.
(a) 53°. (b) 45°. (c) 37°.