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Instructor(s): F.E. Dunnam
PHYSICS DEPARTMENT
1st Exam
PHY 2054
Name (print, last first):
11 June 2002
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 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 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.
Useful (??) Constants:
k = 9 × 109 Nm2 /C 2
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
C=coulomb µ = “micro-” = 10−6
A = ampere “pico” = 10−12 n = “nano” = 10−9 proton charge = +e
proton mass = 1.67 × 10−27 kg
acceleration due to gravity = g = 9.8 m/s2
1. Point charges q of equal magnitude and opposite polarity are
located equidistant from the origin along the y-axis as shown
at right. The general direction of the electrostatic field at point
x due to this charge distribution is
(1) +y
(2) –y
(3) –x
(4) +x
(5) 45 degrees to x
2. Charges +Q and −Q of equal magnitude lie at the base corners
of an equilateral triangle of side length a as shown at right. A
third charge +q of unknown magnitude lies at the apex of the
triangle. The total force exerted on q is:
(1) parallel to the base
(2) at right angles to the base
(3) toward Q
(4) toward −Q
(5) none of these
3. Refer to the previous question. The work (in J) required to move q from the apex to the center of the baseline is:
(1) zero
(2) kQq/a
(3) 2kqQ/a
(4)
√
2kqQ/a
(5) none of these
4. Refer to the previous two questions. If q = +2Q, the magnitude of the electrostatic force on this charge, in N, is
√
(1) 2kQ2 /a2
(2) 4kQ2 /a2
(3) kQ2 /a2
(4) 2 2kQ2 /a
(5) none of these
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5. An electric lantern is a heavy-duty battery (usually 6-volt) in series with an incandescent bulb and a switch. Here are the
electrical data from one of my lanterns:
Battery terminal voltage (switch OFF):
Battery terminal voltage (switch ON):
Circuit current (switch ON):
5.6 V
4.0 V
0.4 A
This battery’s internal resistance in ohms is:
(1) 4
(2) 14
(3) 1.4
(4) 2.4
(5) none of these
6. In the above example, the operating (“hot”) resistance of the bulb (in ohms) is:
(1) 10
(2) 14
(3) 6.4
(4) 22.4
(5) none of these
(4) 22.4
(5) none of these
7. The power (in watts) dissipated in the bulb is
(1) 1.6
(2) 2.2
(3) 6.4
8. A proton and an electron each have kinetic energy of 104 electron volts, achieved by accelerating each of them from rest
in a uniform electric field. The potential difference in volts through which each must have been accelerated, respectively,
is
(1) 104 , 104
(2) 1.84e7, 104
(3) 104 , 1.84e7
(4) 1.6e–13, 2.9e–13
(5) insufficient data
9. The equipotential surfaces associated with an isolated point charge:
(1)
(2)
(3)
(4)
(5)
are concentric spheres centered at the charge
point radially outward from the charge
are vertical planes
are horizontal planes
are concentric cylinders with the charge on the axis
10. A conducting wire carries a steady current of 2 A. The number of electrons passing a cross section in 2.0 s is
(1) 2.5e19
(2) 1.3e19
(3) 6.3e18m
(4) 2
(5) 4
11. Two protons p1, p2, and an electron e lie equally spaced along a straight line as shown below. Consider the electrostatic
forces on p1. The direction of the force due to p2, that due to e, and of the total force on p1 are, respectively:
p1
(1) left, right, left
(2) right, left, right
p2
e
(3) left, right, right
(4) right, left, left
(5) left, left, left
12. The figure shows six 6-micro-F capacitors connected as indicated. The net or equivalent capacitance between points A and
D , in microF is:
(1) 4
(2) 3
(3) none of these
(4) 6
(5) 9
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13. Refer to the figure above. A 20-volt battery is connected between points A and D until the capacitors are fully charged.
The energy stored in the middle capacitor of the top group, in microJ, is
(1) 133
(2) 120
(3) 266
(4) 1600
(5) none of these
14. Refer to the previous question. The 20-V battery is disconnected, leaving the capacitors fully charged. The circuit is then
broken carefully at points B and C [without disturbing the charges] and B and C are connected together. What, now, is
the potential difference [in volts] between A and D, and is the total stored energy altered?
(1) 40, no
(2) 40, yes
(3) 20, no
(4) 20, yes
(5) none of these
15. Eight isolated identical spherical raindrops are each at a potential V. They coalesce to form a single spherical drop. The
potential of the single drop will be:
(1) 4V
(2) 8V
(3) 2V
(4) V/2
(5) V/8
16. A parallel-plate capacitor has a capacitance of 5 microF. It is charged to 10 microC and isolated; then the plates are
pulled apart so that the capacitance becomes 2 microF. The work done by the pulling agent, in microJ, is approximately
(1) 15
(2) 30
(3) zero
(4) 34
(5) 68
17. Two conductors are made of the same material and have the same length. Conductor a is a solid wire of diameter 2 mm.
Conductor b is a hollow tube of inside diameter 2mm and outside diameter 4mm. The ratio of their resistances, Rb/Ra is
(1) 3
(2) 2
(3) 1
(4) 4
(5)
√
2
18. Refer to the figure. A spherical conducting shell has inner and
outer radii of a = 5 cm and b = 7 cm , as shown. A point charge
of +2 microC is placed at the center of the shell’s interior and
a charge of -6microC is placed on the sphere’s surface. The
magnitudes of the electric field and the electric potential at a
distance r = 1 m from the shell’s center are [in kiloV/m and
kiloV, respectively):
(1) 36, 36
(2) 54, 54
(3) 54, 36
(4) 36, 54
(5) none of these
19. Refer to the previous question. The electric field at r = 6 cm from the center (in V/m) is:
(1) zero
(2) 5e6
(3) 2e6
(4) 3.7e6
(5) none of these
20. The magnitude of the electric potential in V at the point r = 6 cm is:
(1) 5e5
(2) 6e5
(3) 9e5
(4) zero
(5) 10.3
THE FOLLOWING QUESTIONS, NUMBERED IN THE ORDER OF THEIR APPEARANCE ON THE ABOVE LIST,
HAVE BEEN FLAGGED AS CONTINUATION QUESTIONS: 3 4 6 7 13 14 19 20