Download 1. Two electromagnetic waves travel through empty space

1. Two electromagnetic waves travel through empty space. Wave A as a wavelength of
700 nm (red light), while Wave B has a wavelength of 400 nm (blue light). Which statement
is true?
A) Wave A travels faster because it has a longer wavelength.
B) Wave B travels faster because it has a higher frequency.
C) The speed of the two waves depends on their amplitudes.
D) Both waves travel at speed c.
E) The speed of the two waves depends on their polarization.
2. The following diagram shows a circular loop of wire in a uniform magnetic field that points
out of the page.
You now perform four separate experiments:
Experiment I: With the loop held stationary, the strength of the magnetic field is
gradually increased.
Experiment II: With the magnetic field held constant, the loop is moved to the right.
The loop remains in the plane of the page and never exits the magnetic field.
Experiment III: With the magnetic field held constant, the loop is shrunk to one half
its initial radius, always remaining within the plane of the page.
Experiment IV: With the magnetic field held constant, the loop is rotated clockwise
about its center, always remaining within the plane of the page.
In which of these experiments will there be an induced current in the loop?
A) I and III
B) I, II, and IV
C) III only
D) I only
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E) I and IV
3. When electricity reaches your house from the
power company, it has an rms voltage of
8,500 V and a frequency of 60 Hz. To
achieve the desired 120 V (rms) household
voltage, a step-down transformer is used, as
shown at right. If the outer transformer coil
(the one connected to the high-voltage line)
contains 25,800 turns of wire, how many
turns should the inner transformer coil (the
one connected to your house) contain?
A) 550
C) 1.8 106
B) 360
Vrms= 8,500 V
D) 3.1 106
E) 620
4. Two plane mirrors meet at right angles at the origin. An object is placed at the point (3,2), as
shown here:
y
x
Which diagram best indicates the location of all the images formed by the mirrors? (Images
are shown as open circles.)
A)
C)
y
B)
y
x
D)
y
x
x
y
E)
y
x
x
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5. A circuit containing a capacitor, an inductor, a generator, and two identical light bulbs is
constructed as shown. The generator produces a peak emf of 10 V. The frequency of the
generator can be varied.
L
C
ω
Bulb A
Bulb B
Examine the following statements about this circuit:
I. Bulb A shines more brightly than bulb B at large frequencies.
II. As approaches zero, bulb A goes out and bulb B continues to shine.
III. The two bulbs have equal brightness when
1 LC .
Which statement(s) are true?
A) I and II
B) II and III
C) I, II, and III
D) III only
E) I and III
6. Lenz's law states that the direction of an induced emf is such that it opposes the change in
magnetic flux. If instead the opposite were the case (i.e. the induced emf reinforced the
change in flux), what fundamental law of physics would be violated?
A) No law would be violated; the direction just happens to be this way.
B) Newton's second law.
C) Conservation of electric charge.
D) Gauss's Law.
E) Conservation of energy.
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Questions 7 and 8 refer to the following figure, which depicts a plane electromagnetic wave.
z
y
E
B
E
B
x
E
B
7. Examine the following statements about this wave:
I. The wave is propagating in the +x direction.
II. This wave could be produced by a charge oscillating back and forth along the y-axis.
III. The wave is linearly polarized.
Which statement(s) are true?
A) I and III
B) III only
C) I, II, and III
D) I only
E) II only
8. If you wanted to detect this wave using an antenna, it would be best to use
A) A linear antenna oriented parallel to the y-axis, or a loop antenna lying in the
x-y plane.
B) A linear antenna oriented parallel to the x-axis, or a loop antenna lying in the
y-z plane.
C) A linear antenna oriented parallel to the z-axis, or a loop antenna lying in the
x-z plane.
D) A linear antenna oriented parallel to the z-axis, or a loop antenna lying in the
y-z plane.
E) A linear antenna oriented parallel to the y-axis, or a loop antenna lying in the
x-z plane.
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9. The Voyager 1 spacecraft, launched in 1977 to explore the outer planets, is presently about
10 billion kilometers away--beyond the orbit of Pluto. However, its radio transmitter
continues to send useful data to scientists on Earth. The rms strength of the electric field
from these transmissions is about 6.8 10 10 V/m. If the signal is received by a radio dish
with an area of 900 m2, what is the rms power incident on the dish?
A) 3.4 10
27
W
B) 1.1 10
18
W
C) 5.6 10
18
W
D) 1.3 10
24
W
E) 4.8 10
12
10. A real object is placed 25 cm away from a mirror with a radius of curvature of 30 cm, as
shown here:
Object
C
The image formed by this mirror will be:
A) real, upright, and magnified.
B) virtual, upright, and reduced.
C) real, upright, and reduced.
D) real, inverted, and magnified.
E) virtual, inverted, and magnified.
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W
Questions 11 and 12 refer to the following AC circuit. It consists of an inductor and a resistor
in series with a generator of frequency f. Internal resistance of the generator is negligible.
L
f
R
11. The impedance of this circuit is:
A) R L
B)
R
2
L
2
C)
R
2
2 fL 2
D)
R2
L2
E)
2 f 2
R
2
2
fL 2
12. In this circuit:
A) resonance will occur if the circuit is driven at the appropriate frequency.
B) the generator performs no work.
C) all of the power is dissipated in the resistor.
D) the voltage and the current are in phase.
E) the current leads the voltage, but if the resistor and the inductor trade positions then
the voltage will lead the current.
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13. You are standing 3.0 m away from the shore of a calm pond that is 26 m wide. An oak tree
grows on the opposite shore. From where you are standing, with your eyes 1.6 m above the
surface of the water, you can just see the reflection of the treetop in the water nearest to your
feet. How tall is the tree?
A) 18.7 m
B) 13.9 m
C) 24.6 m
D) 21.8 m
E) 15.2 m
14. Vertically polarized light with intensity S0 passes through two successive polarizers. The
first has its transmission axis oriented at 30 from the vertical. The second has its
transmission axis oriented at 60 from the vertical. The intensity of the light that emerges
from the second polarizer is
A)
9
S
16 0
B)
1
S
4 0
C)
3
S
8 0
D)
3
S
16 0
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E) zero
15. In the circuit shown here, a conducting bar is free to move on two parallel metal rails. The
two rails are connected by a resistor R. A uniform magnetic field of strength B, directed out
of the page, covers the entire region of this diagram.
R
B out of page
x
You now move the bar as shown in the
position vs. time graph at right.
x
Which of the graphs below best depicts the
current in the resistor as a function of time? A
positive value means that the current is
circulating clockwise; a negative value means
that the current is circulating counterclockwise.
A)
t
C)
B)
I
I
I
t
t
t
E)
D)
I
I
t
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t
16. You are designing a generator that will produce a maximum emf of 170 V when rotated at
an angular speed of 377 rad/s in a magnetic field of strength 0.050 T. You plan to do this by
winding wire around a square frame whose sides have length 12 cm. How many turns of
wire should you use?
A) 891
B) 1370
C) 626
D) 1020
E) 360
17. A shaving/makeup mirror produces an image that is upright and magnified by a factor of
2.5 when your face is 32 cm from the mirror. What is the radius of curvature of the mirror?
A) 84 cm
B) 128 cm
C) 46 cm
D) 224 cm
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E) 107 cm
18. A distant galaxy is receding from us at a speed of 8.0 106 m/s. An alien in that galaxy is
beaming you a distress signal whose wavelength he measures to be 662 nanometers (nm).
What wavelength do you measure for this signal?
A) 610 nm
B) 680 nm
C) 662 nm
D) 730 nm
E) 644 nm
19. In class, we performed the “jumping ring” demonstration, in which a metal ring is placed
on top of a vertical solenoid. At t=0, a switch was closed, causing the current in the solenoid
to rise very quickly from zero to some large value. The ring jumped off the solenoid and hit
the ceiling of the lecture hall. Call this the “original version” of this experiment. Here are
three possible variations:
I. Same as the original version, but the metal ring is replaced by a non-conducting rubber
ring.
II. Same as the original version, but a notch is removed from the ring, so that it resembles
the letter C.
III. With a large, steady current running through the solenoid, a metal ring is placed on
top of the solenoid. At t=0, a switch is opened, causing the current to fall rapidly to
zero.
In which variation(s) will the ring jump up from the solenoid?
A) III only
B) I only
C) II only
D) none of these
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E) I, II, and III
20. The current in a certain circuit is increased at a constant rate from 2.0 A to 7.0 A over a
period of 2.0 s. During this time, an induced emf of 72 mV is observed in the circuit. What
is the self-inductance of this circuit?
A) 48 mH
B) 29 mH
C) 68 mH
D) 18 mH
E) 33 mH
END OF EXAM
Before you go:
1. Check your work carefully. Make sure you have transferred all your answers to your
scantron.
2. BE SURE YOU HAVE FILLED IN YOUR NAME, SECTION, UM-ID,
AND EXAM VERSION NUMBER ON YOUR SCANTRON. Failure to do these
things correctly can result in your grade being delayed or incorrect.
3. Turn in your exam and your scantron at the front of the room. Exams will be
returned to you in your discussion section on Tuesday.