PHYS 121 SAMPLE FINAL EXAM 02 (answers on last page)
1. The force acting on an electron 20 cm from a positive 6.0 x 10-10 C point charge in a vacuum is
A)
B)
C)
D)
E)
21.6 x 10-18 N, attraction
6.8 x 10-10 N, attraction
1.6 x 10-22 N, repulsion
8.0 x 10-21 N, repulsion
9.0 x109 N, repulsion
2. Which of the following describes the intensity of the electrostatic potential near an isolated point
charge?
A)
B)
C)
D)
E)
It remains constant
It varies directly as the distance to the charge
It varies inversely as the distance to the charge
It varies directly as the square of the distance to the charge
It varies inversely as the square of the distance to the charge
3. How much work is required to move a charge of 40 C for a distance of 5 m in the same direction as
the field of 100 V/m?
A)
B)
C)
D)
E)
20 kJ
52 kJ
104 kJ
160 J
800 J
4. A hollow, uncharged conducting sphere has a point charge of +2µC
placed at the center. The charge of the inner surface of the sphere is
A)
B)
C)
D)
E)
zero
+4 µC
–4 µC
+2 µC
–2 µC
5. The charge on the outer surface of the same sphere is
A)
B)
C)
D)
E)
–2 µC
zero
+4 µC
–4 µC
+2 µC
Rev 12/02/04, 12/12/02
6. If an additional net charge of –2 µC is placed on the sphere, the charge on the inner surface will be
A)
B)
C)
D)
E)
–2 µC
zero
+4 µC
–4 µC
+2 µC
7. With this additional charge, the charge on the outer surface will be
A)
B)
C)
D)
E)
–2 µC
zero
+4 µC
–4 µC
+2 µC
8. Twelve coulombs of charge pass through a wire in 4 minutes. What is the average current flowing?
A)
B)
C)
D)
E)
6A
0.05 A
3A
0.1 A
4.8 A
9. A certain wire has resistivity 1 µΩ*m, length L equals 31.4 cm and the diameter d equals 2 mm.
Find its resistance and select the closest answer.
A)
B)
C)
D)
E)
1 kΩ
1 µΩ
10 mΩ
100 mΩ
1Ω
10. The voltage appearing across the 8-ohm resistor is closest to:
A)
B)
C)
D)
E)
80 V
120 V
30 V
27 V
40 V
Rev 12/02/04, 12/12/02
11. Find the current (magnitude and direction)in the single-loop circuit
shown in the sketch
A)
B)
C)
D)
E)
4.5 A, counter-clockwise
1.5 A, clockwise
1.5 A, counter-clockwise
0.5 A clockwise
0.5 A counter-clockwise
12. A current of 2 A flows to the left in the circuit
element shown. If the potential at point A is +1 V,
the potential at point B is
A) 0 V
B) 2 V
C) 8 V
D) 10 V
E) 14 V
13. Two parallel wires, 2 m of length each and separated by a distance of 20 cm, carry currents of 200
A and 50 A in the same direction. Find the interaction force between the wires
A)
B)
C)
D)
E)
zero
0.0002 N, attraction
0.0002 N, repulsion
0.02 N, attraction
0.02 N, repulsion
The circuit at the right applies to the following two
questions :
14. The current through the 2-ohm resistor is
A)
B)
C)
D)
E)
zero
3 A, left
3 A, right
9 A, left
9 A, right
15. The power dissipated by the1-ohm resistor is
A)
B)
C)
D)
E)
10 W
16 W
36 W
100 W
4W
Rev 12/02/04, 12/12/02
16. Find the magnetic energy stored in a coil whose inductance L = 100 H when it is carrying a
current of 0.2 A.
A)
B)
C)
D)
E)
5.0 J
3.14 J
0.02 J
0.2 J
2.0 J
17. A parallel plate capacitor has plate area A, plate separation distance d, and a dielectric material
separating the plates whose permittivity is κ . The capacitance of the capacitor is:
A)
B)
C)
D)
E)
directly proportional to A and κ, but inversely proportional to d
inversely proportional to A, κ and d
directly proportional to A, κ and d
directly proportional to A, but inversely proportional to κ and d
directly proportional to κ and d, but inversely proportional to A
18. Two initially uncharged capacitors of 3.6 and 4.8 µF, respectively, are connected in parallel to a
100-V, dc source. The total charge taken that will be stored in the capacitors is most nearly
A)
B)
C)
D)
E)
84 mC
9C
200 µC
840 µC
21 mC
19. Two initially uncharged capacitors of 5 µF each, are connected in series to a 200-V, dc source.
The total charge that will be stored in the capacitors is most nearly
A)
B)
C)
D)
E)
2000 µC
5 µC
50 µC
500 µC
20 µC
20. What is the equivalent capacitance between terminals A and B in
the following circuit?
A) 7.33 µF
B) 5 µF
C) 7.5 µF
D) 9.00 µF
E) 4.33 µF
Rev 12/02/04, 12/12/02
21. How long will it take to charge the capacitor shown to 50%
of the battery voltage in the circuit at right, if the capacitor
initially has no charge?
A)
B)
C)
D)
E)
1.0 ms
1.4 ms
2.0 ms
2.4 ms
3.0 ms
22. A positive charge is moving right in a region where a uniform magnetic field is directed out of
the page. The magnetic force on the particle is directed:
A)
B)
C)
D)
E)
right
left
up
down
out of the page
23. A constant magnetic field exerts a force on a charged particle:
A)
B)
C)
D)
E)
never
always
if the particle is at rest
if the particle is moving in the direction of the field
if the particle is moving across field lines
The figure at the right applies to the following three questions. A long
straight wire is in the same plane as the rectangular conducting loop.
24. If the current in the long wire is increased, the induced current in the
loop is
A)
B)
C)
D)
E)
clockwise
counterclockwise
zero
downward on both left and right sides of the loop
upward on both left and right sides of the loop
25. If the current in the straight wire remains constant but the loop is
moved to the right, the induced current in the loop is
A) clockwise
B) counterclockwise
C) zero
D) downward on both left and right sides of the loop
E) upward on both left and right sides
Rev 12/02/04, 12/12/02
26. If the current in the straight wire remains constant but the loop is moved up the induced current in
the loop is
A)
B)
C)
D)
E)
clockwise
counterclockwise
zero
downward on both left and right sides of the loop
upward on both left and right sides of the loop
27. A wire slides to the right with a speed of 10 m/s on
two metallic wires 50 cm apart that are connected by a 0.5
Ohm resistor. The slider moves in a region where the
magnetic field is 1 T into the page. The magnitude and
direction of the current through the resistor are
A)
B)
C)
D)
E)
1 A, up
1 A, down
10 A, up
10 A, down
zero
28. A 10-microfarad capacitor has been charged to a potential of 150 volts. A resistor of 50 ohms is
then connected to a capacitor thorough a switch. When the switch is closed for 10 time constants, the
energy dissipated in the resistor is most nearly
A)
B)
C)
D)
E)
9.0 x 103 joules
9.0 x 101 joules
1.1 x 101 joule
1.1 x 10-1 joules
1.0 x 10-7 joules
29. A series RLC circuit driven by an AC voltage contains a capacitor C = 30 mF , an inductor L =
48 H, and resistance R = 40 Ω . What is the impedance at resonant frequency?
A)
B)
C)
D)
E)
480 Ω
40 Ω
28 Ω
48 Ω
30 Ω
Rev 12/02/04, 12/12/02
30. An ideal transformer has 400 primary turns and 40 secondary turns. What is the secondary
voltage if the primary voltage is 340 V?
A)
B)
C)
D)
E)
170 V
3.4 V
340 V
34 V
3400 V
31. If 0.5 A flows in the secondary and 50 A flows in the primary of an ideal transformer, what is the
primary to secondary turns ratio?
A)
B)
C)
D)
E)
1:100
1:10
1:1
10:1
100:1
32. In the circuit shown at right, L = 2.0 H., R = 5 Ohms, and the
battery voltage is 10 V. Find the current flowing through the
resistor in the circuit when the time is t = 0.5 s after the switch is
closed.
A)
B)
C)
D)
E)
0.43
1.43
2.43
3.43
2A
A
A
A
A
33. For the previous circuit, the current through the 5-ohm resistor immediately after the switch is
closed (t=0) and a long time after that (t=∞) are
A)
B)
C)
D)
E)
5 A at t=0 and zero at t=∞
2 A at t=0 and zero at t=∞
zero at t=0 and zero at t=∞
zero at t=0 and 2 A at t=∞
zero at t=0 and 5 A at t=∞
34. Consider an RC circuit, shown at the right, with C = 2
mF. The current through the 5-kOhm resistor immediately after
the switch is closed (t=0) and a long time after that (t=∞) is
A)
B)
C)
D)
E)
5 mA at t=0 and zero at t=∞
2 mA at t=0 and zero at t=∞
zero at t=0 and zero at t=∞
zero at t=0 and 2 mA at t=∞
zero at t=0 and 5 mA at t=∞
Rev 12/02/04, 12/12/02
For the following 6 questions, consider a 240 V (RMS), 60 Hz voltage source applied to a series circuit
consisting of a 50-ohm resistor, a 0.5 H inductor and a 20 µF capacitor.
35. The capacitive reactance of the circuit is about
A) 103 Ω
B) 113 Ω
C) 123 Ω
D) 133 Ω
E) 143 Ω
36. The inductive reactance of the circuit is about
A) 208 Ω
B) 198 Ω
C) 188 Ω
D) 178 Ω
E) 168 Ω
37. The impedance of the circuit is about
A) 188Ω
B) 50Ω
C) 75Ω
D) 100Ω
E) 133Ω
38. The RMS current in the circuit is about
A) 240 A
B) 75 A
C) 6.4 A
D) 4.8 A
E) 3.2 A
39. The average power consumed in this circuit is
A) 256 W
B) 27.7 W
C) 51.2 KW
D) 512W
E) 277 W
40. If the inductance could be changed to maximize the current through the circuit, the new inductance
would be about
A) 392 mH
B) 372 mH
C) 352 mH
D) 332 mH
E) 312 mH
Rev 12/02/04, 12/12/02
Answers to Physics 121 Sample Final Exam 02
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A
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A
E
E
A
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B
D
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E
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D
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B
A
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D
B
D
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B
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B
D
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E
D
C
Rev 12/02/04, 12/12/02