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Instructor: Prof. P. Kumar
PHYSICS DEPARTMENT
PHY 2049
Final Exam
August 4, 2008
Signature:
Name (print, last first):
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 = 4π × 10−7 T m/A NA = 6.02 × 1023 atoms/mole
c = 3 × 108 m/s
µB = 9.27 × 10−24 J/T
1. A horizontal beam of unpolarized light is incident upon a stack of 4 polarizers with axes of polarization, in order and
measured clockwise from the vertical, at 30◦ , 75◦ , 120◦ and 180◦ . What is the ratio of the intensity of the transmitted
beam to that of the incident beam?
(1) 0.031
(2) 0.063
(3) 0.023
(4) 0.047
(5) 0.0063
2. The average intensity of light from an incandescent light bulb is 300 mW/m2 on a particular surface. Assuming that
the light is in the form of an electromagnetic plane wave, what is the maximum magnetic Field amplitude, Bm ?
(1) 5 × 10−8 T
(2) 7 × 10−8 T
(3) 3.5 × 10−8 T
(4) 21 T
(5) 15 T
3. A dimmer for a stage light at a theater consists of a variable inductor, whose inductance is adjustable between zero and
Lmax , connected in series with a light bulb. The electrical supply is 120 V (rms) at 60.0 Hz; the light bulb is rated at
1.0 kW for this voltage. What Lmax is required if you want the rate of energy dissipation in the light bulb to be variable
by a factor of 10 from its upper limit of 1.0 kW? Assume that the resistance of the light bulb does not depend on its
temperature.
(1) 0.11 H
(2) 0.45 H
(3) 1.2 H
(4) 65 mH
(5) 21 mH
4. A cylindrical copper rod has resistance R. It is reformed to three times its original length with no change of volume.
Its new resistance is:
(1) 9R
(2) 2R
(3) R
(4) 4R
(5) R/2
5. Consider the circuit shown in the accompanying figure, where R1 =
13.0Ω and R2 = 7.5Ω. What is the current i3 in A?
(1) 1.46
(2) 2.93
(3) 9.74
(4) 7.69
(5) 12.2
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6. A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A
0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The magnetic force
on either of the two equal sides has a magnitude of:
(1) 0.15 N
(2) 0.105 N
(3) 0
(4) 0.21 N
(5) 0.25 N
7. Two identical conducting spheres A and B carry equal charge. They are separated by a distance much larger than their
diameters. A third identical conducting sphere C is uncharged. Sphere C is first touched to A, then to B, and then
removed. Finally, spheres A and B are brought into contact and then separated. As a result, the electrostatic force
between A and B, which was originally F, becomes:
(1) 25F/64
(2) F/2
(3) F/4
(4) 5F/8
(5) 3F/8
8. An air filled parallel plate capacitor has a capacitance of 4µF. If the separation between the plates is decreased by a
factor of 2 and a material with a dielectric constant of 12 (like Silicon) is inserted between the parallel plates, what is
the new capacitance, in units of µF?
(1) 96
(2) 48
(3) 4
(4) 24
(5) 0.67
9. Charges are arranged on a square of side d as shown in the diagram.
What is the potential at the center of the square (in units of kQ/d),
assuming V = 0 at infinity?
(1) −7.7
(2) +1.3
(3) −9.5
(4) 0.50
(5) +0
10. A double slit experiment is performed with light of wavelength 500 nm. The slits are 1.40 mm apart, and the viewing
screen is 4.20 m from the slits. How far apart (in mm) are the bright fringes near the center of the interference pattern?
(1) 1.5
(2) 2.2
(3) 0.93
(4) 2.5
(5) 3.6
11. The speed of sound in air is 343 m/s under normal conditions. Sound waves of frequency 5700 Hz from a distance source
strike a very high fence of total length 20 m with 20 cm wide vertical gaps spaced 1.4 m apart. At what angle is the 3rd
order maximum of the diffracted spectrum?
(1) 7.4◦
(2) 64.5◦
(3) 17.5◦
(4) 2.5◦
(5) 22.3◦
12. An observer views an object through a diverging lens, whose focal length is 5 cm. If the object is located 10 cm from
the lens, what is the lateral magnification of the object?
(1) 0.33
(2) 0.50
(3) 1.0
(4) 2.0
(5) 0
13. A person standing between two vertical parallel mirrors A and B looks into mirror A. The distance between the two
mirrors is 3 m, and a lit candle is positioned 1 m from mirror A. How deep behind this mirror does the second image of
the candle appear, in meters?
(1) 5
(2) 2
(3) 3
(4) 4
(5) 6