Exam #1, PHYS 102
Chapters 16, 17, & 18
Name_________________________________
8 February 2006
Constants
k=9x109 Nm 2/C2
m proton=1.673x10-27 kg
eo=8.85x10-12 F/m
m electron= 9.1x10-31 kg
e = 1.6x10-19 C
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) An equipotential surface must be
1)
A) perpendicular to the electric field at any point.
B) parallel to the electric field at any point.
2) It takes 50 J of energy to move 10 C of charge from point A to point B. What is the potential
difference between points A and B?
A) 0.50 V
B) 50 V
C) 500 V
D) 5.0 V
3) A surface on which all points are at the same potential is referred to as
3)
A) an equipotential surface.
B) a constant electric force surface.
C) an equivoltage surface.
D) a constant electric field surface.
4) A parallel-plate capacitor is constructed with plate area of 0.40 m2 and a plate separation of 0.10
mm. How much energy is stored when it is charged to a potential difference of 12 V?
A) 10 mJ
B) 5.0 mJ
C) 7.5 mJ
B) no change
C) becomes smaller
4)
D) 2.5 mJ
5) A dielectric material such as paper is placed between the plates of a capacitor. What happens to
the capacitance?
A) becomes larger
2)
5)
D) becomes infinite
6) Two point charges each have a value of 3.0 C and are separated by a distance of 4.0 m. What is the
electric field at a point midway between the two charges?
A) 4.5 ˛ 107 N/C
B) 18 ˛ 107 N/C
C) 9.0 ˛ 107 N/C
D) zero
6)
7) A particle with a charge of 4.0 mC has a mass of 5.0 ˛ 10-3 kg. What electric field directed upward
will exactly balance the weight of the particle?
A) 1.2 ˛ 104 N/C
B) 4.1 ˛ 102 N/C
C) 8.2 ˛ 102 N/C
D) 5.1 ˛ 106 N/C
7)
8) A parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the
distance between the plates is halved, what is the new capacitance?
8)
A) C/4
B) 4C
C) 2C
D) C/2
9) What current is flowing if 0.67 C of charge pass a point in 0.30 s?
A) 0.30 A
B) 0.20 A
C) 2.2 A
9)
D) 0.67 A
10) A negatively charged rod is brought near one end of an uncharged metal bar. The end of the metal
bar farthest from the charged rod will be charged
A) positive.
B) neutral.
C) negative.
D) none of the given answers
1
10)
11) A coulomb per second is the same as
11)
A) a watt.
B) a volt per second.
C) an ampere.
D) a volt-second.
12) The electric field shown
12)
FIGURE 16-2
A) is uniform.
B) decreases down.
C) increases down.
D) decreases to the right.
E) increases to the right.
13) A positive object touches a neutral electroscope, and the leaves separate. Then a negative object is
brought near the electroscope, but does not touch it. What happens to the leaves?
13)
A) They are unaffected.
B) They move closer together.
C) They separate further.
D) cannot be determined without further information
14) What charge appears on the plates of a 2.0-mF capacitor when it is charged to 100 V?
A) 100 mC
B) 200 mC
C) 150 mC
D) 50 mC
15) Materials in which the electrons are bound very loosely to the nuclei and can move about freely
within the material are referred to as
A) conductors.
B) superconductors.
C) insulators.
D) semiconductors.
14)
16) Two charged objects attract each other with a certain force. If the charges on both objects are
doubled with no change in separation, the force between them
15)
16)
A) halves.
B) quadruples.
C) doubles.
D) increases, but we can't say how much without knowing the distance between them.
17) A device that produces electricity by transforming chemical energy into electrical energy is called a
A) battery.
B) generator.
C) transformer.
D) none of the given answers
18) A kilowatt-hour is equivalent to
A) 3,600,000 J/s.
17)
18)
B) 3600 s.
C) 3,600,000 J.
2
D) 1000 W.
19) A proton, initially at rest, is accelerated through an electric potential difference of 500 V. What is
the kinetic energy of the proton?
A) 1.6 ˛ 10-19 J
B) 8.0 ˛ 10-17 J
C) zero
D) 500 J
19)
20) How much energy does a 100-W light bulb use in 8.0 hours?
20)
A) 13 kWh
B) 0.0080 kWh
C) 0.80 kWh
D) 800 kWh
21) A 110-V hair dryer is rated at 1200 W. What current will it draw?
A) 0.090 A
B) 12 A
C) 1.0 A
21)
D) 11 A
22) Is it possible to have a zero electric field value between two positive charges along the line joining
the two charges?
22)
A) No, a zero electric field cannot exist between the two charges.
B) Yes, regardless of the magnitude of the two charges.
C) Yes, if the two charges are equal in magnitude.
D) cannot be determined without knowing the separation between the two charges
23) The resistance of a wire is defined as
23)
A) (current)/(voltage).
B) (current)*(voltage).
C) (voltage)/(current).
D) none of the given answers
24) A 1.0-mm diameter copper wire (resistivity 1.68 ˛ 10-8 Wœm) carries a current of 15 A. What is the
potential difference between two points 100 m apart?
A) 23 V
B) 12 V
C) 32 V
24)
D) 41 V
25) Consider two copper wires. One has twice the length of the other. How do the resistivities of these
two wires compare?
25)
A) The longer wire has twice the resistivity of the shorter wire.
B) The longer wire has four times the resistivity of the shorter wire.
C) Both wires have the same resistivity.
D) none of the given answers
26) The direction of convention current is taken to be the direction that
A) positive charges would flow.
26)
B) negative charges would flow.
27) Doubling the voltage across a given capacitor causes the energy stored in that capacitor to
A) double.
B) quadruple.
C) reduce to one fourth.
D) reduce to one half.
28) Electric field lines near positive point charges
27)
28)
A) radiate inward.
B) radiate outward.
C) circle clockwise.
D) circle counter-clockwise.
29) If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will
A) increase by a factor of four.
B) increase by a factor of two.
C) decrease to one-fourth its original value.
D) decrease to one-half its original value.
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29)
30) The absolute potential at a distance of 2.0 m from a positive point charge is 100 V. What is the
absolute potential 4.0 m away from the same point charge?
A) 25 V
B) 50 V
C) 400 V
D) 200 V
31) A charge of 60 mC is placed on a 15 mF capacitor. How much energy is stored in the capacitor?
A) 120 J
B) 4.0 J
C) 120 mJ
30)
31)
D) 240 mJ
32) Sphere A carries a net positive charge, and sphere B is neutral. They are placed near each other on
an insulated table. Sphere B is briefly touched with a wire that is grounded. Which statement is
correct?
32)
A) Sphere B is now positively charged.
B) Sphere B remains neutral.
C) Sphere B is now negatively charged,
D) The charge on sphere B cannot be determined without additional information.
33) Two 3.00-mC charges are at the ends of a meter stick. Find the electrical potential for the center of
the meter stick.
A) 5.40 ˛ 104 V
B) zero
C) 1.08 ˛ 105 V
D) 2.70 ˛ 104 V
33)
34) The absolute potential at the center of a square is 3.0 V when a charge of +Q is located at one of the
square's corners. What is the absolute potential at the square's center when a second charge of -Q
is placed at one of the remaining corners?
34)
A) 9.0 V
B) 6.0 V
C) zero
D) 3.0 V
35) A light bulb operating at 110 V draws 1.40 A of current. What is its resistance?
A) 154 W
B) 12.7 W
C) 109 W
35)
D) 78.6 W
36) The charge carried by one electron is e = -1.6 ˛ 10-19 C. The number of electrons necessary to
produce a charge of -1.0 C is
A) 6.25 ˛ 1018.
B) 1.6 ˛ 1019.
C) 6.25 ˛ 109 .
D) none of the given answers
37) Three identical point charges of 2.0 mC are placed on the x-axis. The first charge is at the origin, the
second to the right at x = 50 cm, and the third is at the 100 cm mark. What are the magnitude and
direction of the electrostatic force which acts on the charge at the origin?
A) 0.18 N left
36)
B) 0.36 N right
C) 0.36 N left
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D) 0.18 N right
37)
Answer Key
Testname: TEST1_FINAL
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