Download Physics 202 Midterm Exam 3 Nov 30th, 2011

Physics 202 Midterm Exam 3
Nov 30th, 2011
Name: ___________________________________ Student ID: ______________
Section: ___________________________________
TA (please circle):
Daniel Crow
Aaron Levine
Scott Douglas
Andrew Loveridge
Yutao Gong
Taylor Klaus
Jason Milhone
Hojin Yoo
Instructions:
1. Don't forget to write down your name, student ID#, and section number. You need to do this on
this page of your test book and on your Scantron sheet as well, where you should fill in your
student ID number under Identification Number and your three digit section number starting with
"3" under special codes.
2. Answer all multiple questions in this test book by indicating the best answer among choices.
You must do this both on your test book and on your Scantron sheet. Follow instructions on the
Scantron sheet on how to mark valid answers.
3. When you finish, you need to turn in both this test book and the Scantron sheet.
4. Use the blank sides of question pages as additional draft spaces. An extra bank sheet is provided
at the end of the test book.
5. Only one answer is allowed per problem/question/ All problems have equal weight.
Constants: ke = 8.99 x 109 Nm2 /C2
electric vacuum permittivity ε0 = 8.85x10- 1 2 C2 /(Nm2 )
magnetic vacuum permeability µ0 = 4πx10- 7 Tm/A
Area of a sphere: 4πr2 , Volume of a sphere: (4/3)πr3
Speed of light: c = 3.00x108 m/s
Page 1
1. For the current in a stationary circuit to induce a current in an independent stationary
circuit, it is necessary for the first circuit to have
A) a steady current.
B) a large current.
C) no current.
D) a changing current.
E) None of these is correct.
2. After you measure the self-inductance of a coil, you unwind it and then rewind half the
length of wire into a coil with the same diameter and length but half the number of turns.
How does this change the self-inductance?
A) it is the same
B) it is doubled
C) it is quadrupled
D) it is halved
E) it is quartered
3. For the two solenoids above, if l = 50.0 cm, N1 = 250 turns and r1 = 5.0 cm and r2 = 10.0
cm, the mutual inductance of the two solenoids M = 0.7896 mH. What is the number of
turns N2 , in the second solonoid.
A)
B)
C)
D)
E)
250 turns
160 turns
40 turns
200 turns
None of these is correct.
Page 2
4. A region of space contains a magnetic field of 500.0 G and an electric field of 3.00 × 106 N/
C. The total energy density in a cubical box of side = 0.200 m in this region is
A) 19.4 kJ/m3
B) 12.2 kJ/m3
C) 1.03 kJ/m3
D) 66.9 J/m3
E) 24.6 J/m3
5. An LR circuit has a resistance R = 25 Ω, an inductance L = 5.4 mH, and a battery of EMF =
9.0 V. How much energy is stored in the inductance of this circuit when a steady current is
achieved?
A) zero
B) 0.35 J
C) 0.35 mJ
D) 0.70 mJ
E) 0.97 mJ
6. What is the time constant of an RL circuit with a resistance R = 25 Ω and an inductance L =
5.4 mH?
A) 7.4 s
B) 4.6 s
C) 0.14 s
D) 0.22 ms
E) 1.5 ms
7. An exactly 200-turn coil rotates in a magnetic field of magnitude 0.25 T at a frequency of
60.0 Hz. The area of the coil is 5.0 cm2 . What is the maximum EMF in the coil?
A) 1.5 V
B) 4.5 V
C) 9.0 V
D) 9.4 V
E) 24 V
Page 3
8. As the frequency in this simple AC circuit increases, the rms power dissipated by the
resistor
A)
B)
C)
D)
E)
increases.
does not change.
may increase or decrease depending on the magnitude of the original frequency.
may increase or decrease depending on the magnitude of the resistance.
decreases.
9. In the U.K. the power companies supply an rms voltage of 240 V to most home outlets. If
you were to try and use your standard U.S. rated 1200-W (at 120-V) hair dryer in the U.K.
without using a transformer, what would be the average power supplied to the hair dryer?
A) 1200 W
B) 2400 W
C) 4800 W
D) 600 W
E) None of the above
10. Which of the following statements about an inductor that is connected to an AC voltage is
true?
A) The average power dissipated by the inductor is zero.
B) At low frequencies the inductor behaves like a short circuit.
C) At high frequencies the inductor behaves like an open short circuit.
D) The back EMF produced by the inductor is the maximum when the voltage is at zero
part of the cycle.
E) All the above statements are true.
11. A 5.00-µF capacitor is charged to 30.0 V and is then connected across a 10.0-µH inductor.
The frequency of oscillation of the energy stored in the electric field of the capacitor and the
magnetic field of the inductor is
A) 1.41 × 105 Hz
B) 7.07 × 104 Hz
C) 2.25 × 104 Hz
D) 3.18 × 109 Hz
E) 2.00 × 101 0 Hz
Page 4
12. The differential equation for this circuit is
L dI/dt + Q/C = 0
Because I = dQ/dt, the solution is
A)
B)
C)
D)
E)
a wave.
a constant current.
a simple harmonic oscillation.
an exponential decay process.
an exponential growth process.
13. A series RLC circuit is driven by a 1.00-kHz oscillator. The circuit parameters are Vrms =
12.0 V, L = 5.00 mH, C = 4.00 µF, and R = 10.0 Ω. Under steady-state conditions, the rms
potential difference across the resistor will be
A) 5.13 V
B) 9.19 V
C) 12.3 V
D) 14.7 V
E) 18.8 V
Page 5
14. Maxwell generalized Ampère's law to read
from which the displacement current is defined as
A)
B)
C)
D)
E)
15. Which of the following statements contradicts one of Maxwell's equations?
A) A changing magnetic field produces an electric field.
B) The net magnetic flux through a closed surface depends on the current inside.
C) A changing electric field produces a magnetic field.
D) The net electric flux through a closed surface depends on the charge inside.
E) None of these statements contradict any of Maxwell's equations.
16. The electric field of an electro-magnetic wave is given by Ey = 25 sin(2.4 × 106 π (x – 3.0 ×
108 t)). What is the wavelength of the wave?
A) 4.8 × 107 m
B) 2.1 × 10– 8 m
C) 2.1 × 10– 7 m
D) 8.3 × 10– 7 m
E) 7.5 × 10– 6 m
17. What is the frequency of 555-nm light?
A) 16.7 kHz
B) 5.40 × 101 4 Hz
C) 5.40 × 101 5 Hz
D) 1.70 × 107 Hz
E) 5.40 × 101 7 Hz
Page 6
18. The detection of radio waves can be accomplished with either a dipole antenna or a loop
antenna. The dipole antenna detects the _____ of the wave, and the loop antenna detects
the _____ field of the wave.
A) electric field; electric
B) electric field; magnetic
C) magnetic field; magnetic
D) magnetic field; electric
E) electric and magnetic fields; electric
19. A 60.0-W light bulb emits spherical electromagnetic waves uniformly in all directions. If
50.0% of the power input to such a light bulb is emitted as electromagnetic radiation, what
is the radiation intensity at a distance of 2.00 m from the light bulb?
A) 15 W/m2
B) 4.8 W/m2
C) 2.4 W/m2
D) 0.60 W/m2
E) 1.2 W/m2
20. The rms value of the electric field in an electromagnetic wave is Erms = 0.600 kV/m. The
average energy density of this wave is approximately
A) 0.796 µJ/m3
B) 1.59 µJ/m3
C) 3.18 µJ/m3
D) 6.78 µJ/m3
E) 5.21 µJ/m3
Page 7
Answer Key - Midterm3_draft_exam
1.
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D
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B
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B
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B
B
D
C
Page 8