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PHYSICS DEPARTMENT
PHY 2054
2nd Exam [CJ Ch. 25{27]
Name (print):
13 July 1999
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 green answer sheet (use 76{80 for the 5-digit number). Code your name
on your answer sheet. Darken circles completely (errors can occur if too light). 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) If there is no answer close enough to be correct, the correct answer is to leave the question blank. You should not
expect many of these.
(5) Blacken the circle of your intended answer completely, using a number 2 pencil. Do not make any stray
marks or the answer sheet may not read properly.
(6) Good luck!!!!
Have fun!!!
>>>>>>>>BEFORE YOU FINISH <<<<<<<<
Make sure your test number is coded in correctly. Your test score will be posted under this number, so write it down and
take it with you Hand in the exam and the green answer sheet separately.
Useful (??) Constants:
¹0 = 4¼ £ 10¡7 Tm/A
²0 = 8:85 £ 10¡12 C2 /(Nm2 )
electron charge = ¡1:6 £ 10¡19 C
electron mass = 9:11 £ 10¡31 kg
V=volt
N=newton
J=joule
m=meter
W=watt ¹ = \micro-" = 10¡6
A = ampere \pico" = 10¡12 n = \nano" = 10¡9 m = \milli" = 10¡3 proton mass = 1:67 £ 10¡27 kg
c = 3 £ 108 m/s
1. A car travels northward at 75 km/h along a straight road in a region where the earth's magnetic ¯eld has a vertical
component of 0:50 £ 10¡4 T. The emf (in millivolts) induced between the left and right side, separated by 1.7 m, is:
(1) 1.8
(2) 0
(3) 3.6
2. The ¯gure shows a uniform magnetic ¯eld which is normal to the plane
of a conducting circular loop of resistance 1.5- and radius 0.024 m. The
magnetic ¯eld has a magnitude of 3.0 T and is directed out of the paper.
The area of the rectangular portion of the loop is negligible compared
to that of the circular loop. What is the average current in the loop if
the magnitude of the magnetic ¯eld is doubled in 0.4 s? .
(1)
(2)
(3)
(4)
(5)
9:0 £ 10¡3
2:8 £ 10¡3
4:5 £ 10¡3
4:5 £ 10¡3
9:0 £ 10¡3
A,
A,
A,
A,
A,
clockwise
clockwise
clockwise
counter-clockwise
counter-clockwise
(4) 6.4
(5) 13
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3. A long, straight wire carries a 10.0 A current in the + y direction as shown
in the ¯gure. Next to the wire is a square copper loop that carries a 2.0 A
current as shown. The length of each side of the square is 1.0 m. Determine
the magnitude of the net force that acts on the loop.
(1) 1:7 £ 10¡5 N
(2) 8:0 £ 10¡6 N
(3) 1:1 £ 10¡5 N
(4) 1:4 £ 10¡5 N
(5) 2:3 £ 10¡5 N
4. A single circular loop of 1.0 m radius carries a current of 10.0 mA. It is
placed in a uniform magnetic ¯eld of magnitude 0.50 T that is directed
parallel to the plane of the loop as suggested in the ¯gure. What is the
magnitude of the torque exerted on the loop by the magnetic ¯eld? .
(1) 1:57 £ 10¡2 N¢m
(2) 3:14 £ 10¡2 N¢m
(3) 6:28 £ 10¡2 N¢m
(4) 9:28 £ 10¡2 N¢m
(5) 10 N¢m
5. The passenger-side rear-view mirror on most cars is of what type (plane, concave/converging, or convex/diverging)
and for what principal reason?
(1)
(2)
(3)
(4)
(5)
convex, to yield a wider ¯eld of view to the driver
concave, for a brighter image to the driver
plane, to minimize distortion
convex, to avoid focussing the sun's rays
concave, to maximize spherical aberration
6. In each of the following operations, energy is expended. Indicate the one that yields the LEAST percentage of
returnable/reusable electrical energy:
(1)
(2)
(3)
(4)
(5)
sending current through a resistor
charging a capacitor
charging a storage battery
establishing a current in an inductor
moving a conducting rod in a magnetic ¯eld
7. A current of 10 A in a certain inductor results in a stored energy of 40 J. When the current is changed to 5 A in the
opposite direction, the stored energy (in J) changes by:
(1) 30
(2) 20
(3) 40
(4) 50
(5) 60
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8. A point source emits electromagnetic energy at an average rate of 100 W. The intensity 10 m from the source (in
W/m2 )is:
(1) 0.080
(2) 0.024
(3) 1.0
(4) 1.6
(5) 10
9. From the data given in the previous question, the rms value of the electric ¯eld (in V/m) at the 10 m location will be:
(1) 5.5
(2) 7.7
(3) 3.9
(4) 30
(5) 95,000
10. Polarization experiments provide evidence that light is:
(1) a transverse wave (2) a longitudinal wave (3) refractive (4) a stream of particles (5) nearly monochromatic in
vacuum
11. A vertical automobile radio antenna is sensitive to electric ¯elds that are polarized:
(1)
(2)
(3)
(4)
(5)
vertically
horizontally
in circles around the antenna
normal to the antenna in the forward direction
none of these
12. A light bulb placed at eye-level burns in front of the center of a 40-cm wide mirror that is hung vertically on a wall.
A man walks in front of the mirror along a line that is parallel to the mirror/wall and twice as far from it as the bulb.
The greatest distance (in cm) he can walk and still see the image of the bulb is:
(1) 120
(2) 80
(3) 60
(4) 40
(5) 20
13. The image produced by a convex mirror of an erect object in front of the mirror is always:
(1)
(2)
(3)
(4)
(5)
virtual, erect, and smaller than the object
virtual, erect, and larger than the object
real, erect, and larger than the object
real, erect, and smaller than the object
none of these
14. A concave mirror forms a real image which is twice the size of the object. If the object is 20 cm from the mirror, the
radius of curvature of the mirror (in cm) must be about:
(1) 27
(2) 13
(3) 20
(4) 40
(5) 80
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15. The term \virtual" as applied to an image made by a mirror means that the image:
(1)
(2)
(3)
(4)
(5)
cannot be shown directly on a screen
is in front of the mirror
cannot be photographed by a camera
is on the mirror surface
is the same size as the object
16. Electrons (mass m, charge {e) are accelerated from rest through a potential di®erence V and are then de°ected by a
magnetic ¯eld B that is perpendicular to their velocity. The radius of the resulting electron trajectory is:
p
p
p
p
(1) (1=B) 2mV =e
(2) (1=B) 2eV =m
(3) B 2eV =m
(4) B 2mV =e
(5) none of these
17. A uniform magnetic ¯eld B lies in the plane of this page and is directed to the left. A conductor carries a current I
straight down (perpendicular) into the page. The magnetic force acting on the wire is toward the
(1) top of the page
(2) bottom of the page
(3) left
(4) right
(5) none|force is zero
18. Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these
currents are doubled and the wire separation tripled, the force per unit length becomes:
(1) 4F=3
(2) 2F=9
(3) 2F=3
(4) 4F=9
(5) 6F
19. The ¯gure shows two concentric metal loops, each carrying a current. The
smaller loop has a radius of 0.04 m. The larger loop carries a current of 8
A and has a radius of 0.06 m. Determine the value of the current in the
smaller loop which will result in the total magnetic ¯eld at the center of
the system being equal to zero.
(1) 5.3 A
(2) 6.0 A
(3) 10.6 A
(4) 12.0 A
(5) 24.0 A
20. An ignition transformer produces electric sparks at 24,000 V from a 12-V primary source. If the primary current is 5
A, what is the approximate turns ratio and the output current?
(1) 2000:1; 2.5 mA
(2) 2000:1; 2 A
(3) 1000:1; 5 mA
(4) 1000:1; 1000A
(5) 2000:1; 5 A