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PHYSICS DEPARTMENT
Instructors: Prof. P. Kumar
PHY 2049
Exam 3
July 21, 2006
Name (print, last first):
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.
DIRECTIONS
(1) Code your test number on your answer sheet (use 76–80 for the 5-digit number). Code your name on your
answer sheet. DARKEN CIRCLES COMPLETELY. Code your student 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. 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 with scratch work most questions demand.
(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 the answer sheet may not read properly.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
>>>>>>>>WHEN YOU FINISH <<<<<<<<
Hand in the answer sheet separately.
Constants
−12
−31
²0 = 8.85 × 10
F/m me = 9.11 × 10
kg
mp = 1.67 × 10−27 kg
e = 1.6 × 10−19 C
k = 9 × 109 N m2 /C2 µ0 = 12.56 × 10−7 H/m NA = 6.02 × 1023 atoms/mole c = 3 × 108 m/s
1. The normal to a certain 1-m2 area makes an angle of 60◦ with a uniform magnetic field. The magnetic flux through
this area is the same as the flux through a second area that is perpendicular to the field if the second area is:
(1) 0.5 m2
(2) 0.866 m2
(3) 1.15 m2
(4) 2 m2
2. A rectangular loop of wire is placed midway between two long
straight parallel conductors as shown. The conductors carry currents i1 and i2 as indicated. If i1 is increasing and i2 is constant,
then the induced current in the loop is:
(1) counterclockwise
(2) zero
(3) clockwise
(5) 1 m2
i1
(4) depends on i1 − i2
i2
(5) depends on i1 + i2
12 cm
3. The circuit shown is in a uniform magnetic field that is into the
page. The current in the circuit is 0.20 A. At what rate is the
magnitude of the magnetic field changing: Is it increasing or decreasing?
10 Ω
12 cm
4V
(1) 140 T/s, decreasing
(2) zero
(3) 140 T/s, increasing
(4) 420 T/s, decreasing
(5) 420 T/s, increasing
4. We desire to make an LC circuit that oscillates at 100 Hz using an inductance of 2.5 H. We also need a capacitance of:
(1) 1 µF
(2) 1 F
(3) 1 mF
(4) 100 µF
(5) 1 pF
5. An LC circuit has a capacitance of 30 µF and an inductance of 15 mH. At time t = 0 the charge on the capacitor is
10 µC and the current is 20 mA. The maximum charge on the capacitor is:
(1) 17 µC
(2) 8.9 µC
(3) 10 µC
(4) 12 µC
(5) 24 µC
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6. The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The
power dissipated by R in this situation is P . If R is connected directly to the source it will dissipate a power of:
(1) P/9
(2) P/3
(3) P
(4) 3P
(5) 9P
~ field at its center is:
7. A bar magnet is placed vertically with its S pole up and its N pole down. The B
(1) down
(2) zero
(3) up due to the weight of the magnet
(4) horizontal
(5) slightly below the horizontal
8. The impedance of the circuit shown is:
100 Ω
0.5 H
200 µF
50 Hz, 240 Vms
(1) 173Ω
(2) 21Ω
(3) 126Ω
(4) 63Ω
9. The diagram shows one plate of a parallel-plate capacitor from
within the capacitor. The plate is circular and has radius R. The
dashed circles are four integration paths have radii of r1 = R/4,
r2 = R/2, r3 = 3R/2, and r4 = 2R. Rank the paths according to
H
~
the magnitude of B·ds
around the paths during the discharging
of the capacitor, least to greatest.
(1) 1, 2, then 3 and 4 tie
(2) 1, 2 and 4 tie, then 3
(3) 1, 2 and 3 tie, then 4
(5) 98Ω
1
2
3 4
(4) 1, 2, 3, 4
(5) all tie
10. Have you filled out the scantron sheet correctly?
(1) yes
(2) why
(3) no
(4) don’t bother
(5) none of these