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Instructor(s): Nakayama/Barrow
PHYSICS DEPARTMENT
Exam 2
PHY 2005
Name (print, last first):
July 12, 2010
Signature:
On my honor, I have neither given nor received unauthorized aid on this examination.
YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.
(1) Code your test number on your answer sheet (use lines 76–80 on the answer sheet for the 5-digit number).
Code your name on your answer sheet. DARKEN CIRCLES COMPLETELY. Code your UFID number on your
answer sheet.
(2) Print your name on this sheet and sign it also.
(3) Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of the
test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout.
(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not
make any stray marks or some answers may be counted as incorrect.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
(6) Hand in the answer sheet separately.
Physical Constants:
µo = 4π × 10−7 N/A2
e = 1.602 × 10−19
me = 9.11 × 10−31 kg
mp = 1.67 × 10−27 kg ²o = 8.85 × 10−12 C2 /Nm2
c = 3 × 108 m/s
1. A 0.40 m long solenoid with 1500 turns carries a current of 2.0 A and has a radius of 10−2 m. What is the strength of
the magnetic field at its center?
(1) 94 × 10−4 T
(2) 39 × 10−4 T
(3) 62 × 10−4 T
(4) 124 × 10−4 T
(5) 73 × 10−4 T
2. In Puerto Rico, the horizontal component of the Earth’s magnetic field is 3×10−5 T, northward. The vertical component
is 4.7 × 10−5 T. What is the magnitude and direction of the force on a 2.0 m length of vertical wire that is carrying a
current of 17 A straight upward?
(1) 1.02 × 10−3 N, westward
(5) 2.06 × 10−3 N, eastward
(2) 1.02 × 10−3 N, eastward
(3) 1.60 × 10−3 N, upward
(4) 2.62 × 10−3 N, westward
3. Which one of the following statements concerning the magnetic force on a charged particle in a magnetic field is true?
(1)
(2)
(3)
(4)
(5)
It
It
It
It
It
depends on the component of the particle’s velocity that is perpendicular to the field.
is a maximum if the particle is stationary.
is zero if the particle moves perpendicular to the field.
is a maximum if the particle moves parallel to the field.
acts in the direction of motion for a positively charge particle.
4. Each of the electrons in the beam of a TV tube has a momentum of 6.7 × 10−23 kg·m/s. If the beam is traveling
perpendicular to Earth’s magnetic field (7.1 × 10−5 T at this location), what is the radius of curvature of its path?
(Recall that p = mv)
(1) 5.89 m
(2) 0.589 m
(3) 5.89 mm
(4) 58.9 m
(5) 0 m
5. The magnitude of the magnetic field 8.0 cm from the axis of a long straight wire is 5.0 × 10−5 T. What must the current
be in the wire if there are no other sources nearby?
(1) 20.0 A
(2) 0.20 A
(3) 10.0 A
(4) 0.10 A
(5) 2.0 A
6. A certain transformer used in a radio changes the 120 V line voltage to 9.0 V. If the primary has 200 turns, how many
turns does the secondary have?
(1) 15
(2) 13
(3) 9
(4) 5
(5) 20
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7. A resistor is connected to a wire that is wrapped around a cylinder as shown
in the figure. A bar magnet oriented as shown is moved toward the cylinder
at speed v. In what direction does the induced current flow through the
resistor?
(1) To the right
(2) To the left
(3) The current varies sinusoidally
(4) There is not enough information
(5) There is no current
N
S
v
8. A rectangular coil that has 50 loops on it is 3 cm × 4 cm. It rotates about an axis that is perpendicular to a magnetic
field of 0.60 T. How fast must the coil rotate if the maximum induced emf in it is to be 100 V?
(1) 442 Hz
(2) 221 Hz
(3) 60 Hz
(4) 2800 Hz
(5) 6000 Hz
9. A square coil, enclosing an area with sides 8.0 cm long, is wrapped with 5000 turns of wire. A uniform magnetic field
perpendicular to its plane is turned on and increases to 0.25 T during an interval of 2.0 s. What is the average current
in the coil if the resistance of the coil is 8 Ω?
(1) 0.5 A
(2) 1.3 A
(3) 2.5 A
(4) 4.1 A
(5) 0.8 A
10. A capacitor with original charge qo is discharged through a resistor. After four time constants have passed, what will be
the voltage across the capacitor (in terms of Vo )?
(1) 0.0183 Vo
(2) 0.0287 Vo
(3) 0.1350 Vo
(4) 0.0038 Vo
(5) 0.0 Vo
11. A current i(t) = 10.0 sin (14t) amperes flows through a 15 Ω resistor. What is the rms voltage of the voltage source?
(1) 106.1 V
(2) 120.0 V
(3) 68.4 V
(4) 150.0 V
(5) 212.1 V
12. When connected across a 60 V, 60 Hz source, a capacitor draws a current of 8.0 mA. What is the capacitance of the
capacitor?
(1) 0.354 µF
(2) 0.824 µF
(3) 1.34 µF
(4) 2.00 µF
(5) 0.174 µF
13. In a series RCL circuit the voltages across the circuit elements are VR = 30 V, VC = 20 V, and VL = 50 V. The current
in the circuit is 3 A. What is the source voltage (rms value)?
(1) 42.4 V
(2) 100.0 V
(3) 76.2 V
(4) 61.6 V
(5) 0.0 V
14. A series ac circuit consisting of a 100 Ω resistor, 1 mH inductor, and a 1 µF capacitor is operated at its resonance
frequency. If the voltage source is 100 V rms, what is the current in the circuit?
(1) 1.0 A
(2) 2.4 A
(3) 0.88 A
(4) 0.50 A
(5) 1.41 A
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15. Cobalt 60 is commonly used in hospitals as a γ ray source. The wavelength of the γ ray it gives off is 0.061 A. Find the
frequency of these waves.
(1) 4.918 × 1019 Hz
(2) 4.918 × 1020 Hz
(3) 1.639 × 1019 Hz
(4) 1.639 × 1020 Hz
(5) 8.215 × 1018 Hz