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Instructor(s): F.E. Dunnam, G. Mitselmakher
PHYSICS DEPARTMENT
PHY 2054
1st Exam
15 February 2005
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.
(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 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.
Constants
−11
2
2
G = 6.67 × 10
Nm /kg
g = 9.80 m/s2
e = 1.6 × 10−19 C
1µC = 10−6 C
kE = 8.99 × 109 Nm2 /C2 me = 9.11 × 10−31 kg
M = “mega” = 106
1nC = 10−9 C
mp = mn = 1.67 × 10−27 kg
c = 3 × 108 m/s
²0 = 8.85 × 10−12 C2 /N/m2 1pC = 10−12 C
1. At a point halfway between two identical point charges, the electric field and the potential, respectively, will be:
(1) zero, non-zero (2) non-zero, non-zero (3) non-zero and equal to one another (4) both zero (5) non-zero, zero
2. Three equal charges, each of +7 microC are arranged at the corners of an equilateral triangle of side length 10 cm.
The magnitude of the electrostatic field at the center of the triangle, in V/m, is
(1) zero
(2) 3.4 × 107
(3) 44
(4) 132
(5) none of these
3. Refer to the previous question. What is the magnitude of the total force (in N) acting on each of the charges?
(1) 76
(2) 44
(3) 88
(4) 38
(5) none of these
4. Refer to the previous question. The electrostatic potential energy of this assembly of charges, in J, is
(1) 13.2
(2) 8.8
(3) zero
(4) 3.4 × 107
(5) none of these
5. An electron with a speed of 2 × 106 m/s moves into a uniform electric field of 500 N/C that is parallel to the electron’s
motion. How long does it take, in nanoseconds, for the electron to come to rest?
(1) 23
(2) 35
(3) 12
(4) 2300
(5) never
6. The electron in the above question initially possessed what kinetic energy, in electron volts?
(1) 11
(2) 35
(3) 24
(4) 2300
(5) 8
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7. 6. Four point-charges are placed on the rim of a circle of radius 10 cm. The charges, in microC, are +0.5, +1.5, −1.0,
and −0.5, respectively. If electrical potential at the center of the circle due to the +0.5 charge alone is 45 kilovolts,
what is the total potential in kilovolts at this point?
(1) 45
(2) 18
(3) −45
(4) −18
(5) zero
8. A parallel-plate capacitor of capacitance C (not connected to anything) has charge Q placed on it, at potential V. If
the plates are carefully moved twice as far apart,
(1)
(2)
(3)
(4)
(5)
the
the
the
the
the
potential becomes 2V
potential becomes V/2
charge becomes 2Q
charge becomes Q/2
capacitance becomes 2C
9. The capacitor in the above question [same initial conditions] has a slab of dielectric (k = 2) carefully inserted between
the plates without touching them. Now
(1)
(2)
(3)
(4)
(5)
the
the
the
the
the
potential becomes V/2
potential becomes 2V
charge becomes 2Q
charge becomes Q/2
capacitance becomes C/2
10. Four identical resistors, each having resistance R, are connected in series across a battery. The current from the battery
is I. The four resistors are then connected in parallel across the same battery. The current is now
(1) 16 I
(2) 4 I
(3) I/4
(4) 1/16
(5) none of these
11. Choose the correct statement(s):
Two pieces of a conducting material are of identical lengths and connected in series. Piece #2 has half the diameter
of #1. When connected across a source of emf, the drift velocity of the charge carriers is:
A. less in #2 than in #1
B. greater in #2 than in #1
C. the same in both #1 and #2
D. approximately the speed of light
E. Independent of the current in #1 and #2
(1) B
(2) A
(3) A, C
(4) C, E
(5) B, D
12. A high voltage transmission line carries 1000 A at 700 kV for a total distance of 100 miles. If the resistance of the line
is 0.1 ohm /mile, what is the ohmic power loss in the line?
(1) 10 MW
(2) 100 kW
(3) 10 kW
(4) 100 MW
(5) None of these
13. A 12-volt battery is connected in series with a 100-ohm resistor and a 30 microfarad capacitor. Immediately after the
switch is closed, the potential difference across the resistor (in volts) is:
(1) 12
(2) zero
(3) 8.33
(4) 3.67
(5) none of these
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C
14. What is the energy stored in the capacitor C2 (in µJ)? C1 = C2 =
C3 = C4 = 3µF.
2
+
10 V
(1) 50
(2) 17
(3) 8
(4) 33
C
C
3
1
(5) 12
15. What is the maximum number of 60-W light bulbs you can connect in parallel to a 120-V circuit without tripping the
30-A circuit breaker?
(1) 59
(2) 11
(3) 35
(4) 6
(5) 29