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.
(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) 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
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.
This question and the next two refer to this
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
(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) 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) 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
(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.