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Physics Exam Preview - Electricity
Multiple Choice - Identify the letter of the choice that best completes the statement or answers the question.
____
1. The charge of an electron is
a. positive.
b. negative.
c. Electrons have no charge.
____
2. Atomic nuclei of almost all elements consist of
a. only neutrons.
b. protons and electrons.
c. neutrons and electrons.
d. only protons.
e. protons and neutrons.
____
3. Two like charges
a. neutralize each other.
b. repel each other.
c. must be neutrons.
d. attract each other.
e. have no effect on each other.
____
4. Protons and electrons
a. attract each other.
b. repel each other.
c. do not interact.
____
5. The fundamental force underlying all chemical reactions is
a. electrical.
b. gravitational.
c. centripetal.
d. nuclear.
e. none of the above
____
6. Electrical forces between charges are strongest when the charges are
a. far apart.
b. close together.
c. The electrical force is constant everywhere.
____
7. Coulomb's law says that the force between any two charges depends
a. directly on the size of the charges.
b. inversely on the square of the distance between the charges.
c. both A and B
d. none of the above
____
8. Two charges are separated by a certain distance. If the magnitude of each charge is doubled, the force on each charge is
a. halved.
b. doubled.
c. tripled.
d. quadrupled.
____
9. When the distance between two charges is halved, the electrical force between the charges
a. doubles.
b. reduces to one fourth.
c. halves.
d. quadruples.
e. none of the above
____
10. The net charge of a nonionized atom
a. depends only on the number of electrons it has.
b. is zero.
c. usually cannot be determined.
d. depends only on the number of protons it has.
____
11. A positive ion has
a. more electrons than protons.
b. more protons than electrons.
c. a +1 charge always.
d. one proton.
____
12. Conservation of charge means that
a. the total amount of charge in the universe is constant.
b. no experimenter has ever seen a single charge destroyed by itself.
c. electrons by themselves can be neither created nor destroyed.
d. charge can be neither created nor destroyed.
e. all of the above
____
13. If you comb your hair and the comb becomes positively charged, your hair becomes
a. uncharged.
b. positively charged.
c. negatively charged.
____
14. To say that electric charge is conserved means that no case has ever been found where
a. the total amount of charge on an object has increased.
b. one object has more charge than another object.
c. the total charge on an object has changed.
d. net charge has been created or destroyed.
e. none of the above
____
15. A difference between electrical forces and gravitational forces is that electrical forces include
a. infinite range.
b. repulsive interactions.
c. the inverse square law.
d. separation distance.
e. none of the above
____
16. The common hydrogen atom consists of
a. one electron.
b. one proton and one electron.
c. one proton.
d. two protons, one neutron, and two electrons.
e. one neutron and one electron.
____
17. In a good insulator, electrons are usually
a. not moving at all.
b. free to move around after an impurity has been added.
c. free to move around.
d. tightly bound in place.
e. semi-free to move around.
____
18. Objects can be charged by
a. induction.
b. friction.
c. touching.
d. all of the above
e. none of the above
____
19. Charge carriers in a metal are electrons rather than protons, because electrons are
a. relatively far from a nucleus.
b. loosely bound.
c. lighter.
d. all of the above
e. none of the above
____
20. To be safe in the unlikely case of a lightning strike, it is best to be inside a building framed with
a. steel.
b. wood.
c. either A or B.
____
21. A conductor differs from an insulator in that a conductor has
a. more protons than electrons.
b. faster-moving molecules.
c. more electrons than protons.
d. more electrons than an insulator.
e. none of the above
____
22. Much electronic equipment contains transistors and diodes that are made from semiconductors. Semiconductors
a. can be very good insulators.
b. can conduct electricity.
c. contain helpful impurities.
d. all of the above
e. none of the above
____
23. A negatively charged rod is brought near a metal can that rests on a wood table. You touch the opposite side of the can
momentarily with your finger. The can is then
a. positively charged.
b. negatively charged.
c. charged the same as it was.
d. uncharged.
____
24.
____
25. Lightning bolts occur between
a. clouds and the ground.
b. clouds.
c. both A and B.
____
26. To charge an object by induction, the process of grounding
a. may or may not occur.
b. always occurs.
____
27. When a charged cloud passes overhead, the ground below is charged by
a. induction.
b. polarization.
c. deduction.
d. electrification.
____
28. Bring a charged object near a conductor and then momentarily touch the conductor. This demonstrates charge by
a. deduction.
b. polarization.
c. induction.
d. electrification.
An electroscope is charged positively, as shown by foil leaves that stand apart. As a negatively charged rod is brought
close to the electroscope, the leaves
a. spread farther apart.
b. do not move.
c. move closer together.
____
29. A rubbed balloon will stick to a wooden wall, which demonstrates charge
a. transfer.
b. potential.
c. conservation.
d. polarization.
____
30. Electrical polarization occurs when
a. an electron is at a different location than a proton.
b. charge distribution in a neutral molecule separates.
c. the electron and the proton are on different sides of an atom.
d. an atom vibrates in a single direction.
e. none of the above
____
31. The reason a charged balloon will stick to a wall is that
a. induced opposite charges in the wall are closer than other wall charges.
b. the rubber of the balloon simply sticks to walls.
c. electrons transfer back and forth between the wall and the balloon.
d. the charge is slightly sticky and acts like glue.
e. none of the above
____
32. The charge distribution in some molecules is permanently separated into positive and negative regions. Such molecules are
called
a. ionized molecules.
b. electric dipoles.
c. coulomb molecules.
d. induced molecules.
e. insulators.
____
33. Two charged particles held close to each other are released. As they move, the force on each particle increases. Therefore,
the particles have
a. opposite signs.
b. the same sign.
c. charges that cannot be determined
____
34. Two charged particles held close to each other are released. As the particles move, the velocity of each increases.
Therefore, the particles have
a. the same sign.
b. opposite signs.
c. charges that cannot be determined.
____
35. A positive charge and a negative charge held near each other are released. As they move, the force on each particle
a. increases.
b. stays the same.
c. decreases.
____
36. Two charged particles held near each other are released. As they move, the acceleration of each decreases. Therefore, the
particles have
a. opposite signs.
b. the same sign.
c. charges that can not be determined.
____
37. How many different kinds of force would act on a proton placed in both an electric field and a gravitational field?
a. one.
b. none.
c. two.
____
38. The SI unit of charge is the
a. ohm.
b.
c.
d.
e.
joule.
coulomb.
ampere.
newton.
____
39. Particle A has twice as much charge as particle B. Compared to the force on particle A, the force on particle B is
a. half as much.
b. two times as much.
c. four times as much.
d. the same.
e. none of the above
____
40. The electrostatic force between two charges located 8 meters apart is 0.10 N. What will the force be between these charges
when they are located 2 meters apart?
a. 0.01 N
b. 0.03 N
c. 0.1 N
d. 0.8 N
e. 1.6 N
____
41. A 2-C charge and a 4-C charge attract each other with 10 N of force. How much will a 2-C charge and a 12-C charge attract
each other when placed the same distance apart?
a. 5 N
b. 12 N
c. 10 N
d. 30 N
e. 60 N
____
42. Two charges separated a distance of 1.0 meter exert a 2.0-N force on each other. If the charges are pushed to a separation of
meter, the force on each charge will be
a.
b.
c.
d.
e.
2.0 N.
1.5 N.
3.0 N.
6.0 N.
18.0 N.
____
43. Two charges separated by a distance of 1 meter exert a 20-N force on each other. If the charges are pulled to a 2 meter
separation distance, the force on each charge will be
a. 0 N.
b. 5 N.
c. 10 N.
d. 40 N.
e. 80 N.
____
44. Two charges separated by a distance of 1 meter exert a 2-N force on each other. If the magnitude of each charge is doubled,
the force on each charge is
a. 2 N.
b. 4 N.
c. 8 N.
d. 16 N.
e. none of the above
____
45. If you walk into a region of space and suddenly feel a force, the space is said to contain a
a. charged object.
b. force field.
c. large charge.
d. black hole.
e. heavy object.
____
46. An electric field has
a. direction.
b. magnitude.
c. Both A and B
____
47. Every proton in the universe is surrounded by its own
a. gravitational field.
b. electric field.
c. both A and B
d. none of the above
____
48. The direction of electric field lines shows the
a. direction of the force on a test positive charge.
b. size of the field.
c. strength of the field.
d. all of the above
____
49. Suppose a hollow metal sphere has a large negative charge on it. The electric field strength inside the sphere is
a. large and positive.
b. zero.
c. weak and negative.
d. weak and positive.
e. large and negative.
____
50. Suppose you touch a negatively charged object to a metal sphere so that electrons move from the charged object onto the
sphere. After the charged object is moved far away, electrons on the sphere will be
a. distributed in small bunches over the sphere's surface.
b. distributed evenly over the sphere's surface.
c. pulled off the sphere along with the charged object.
d. located at the place where the charged object was.
e. all of the above
____
51. Electrical potential energy is the energy a charged object has because of its
a. momentum.
b. location.
c. mass.
d. motion.
e. volume.
____
52. A small, positively charged object near a positively charged sphere is moved closer to the sphere. The electrical potential
energy of the small object
a. stays the same.
b. decreases.
c. increases.
____
53. When an electron is brought near a negatively charged sphere, its potential energy increases. The reason this happens is
that
a. two like charges go from a position far apart to a position close together.
b. negative charges repel each other.
c. work was done to bring the charges together.
d. none of the above
____
54. If two negative charges are held close together and then released, the charges will
a. accelerate toward each other.
b. accelerate away from each other.
c. not move.
d. move at a constant speed away from each other.
____
55. Electric potential is defined as
a. electrical potential energy of a charge multiplied by the quantity of the charge.
b. electrical potential energy of a charge divided by the quantity of the charge.
c. electrical potential energy.
d. gravitational potential.
e. voltage.
____
56. A volt is a unit of
a. charge.
b. electric potential.
c. energy.
d. work.
e. current.
____
57. Suppose a hollow metal sphere has a large number of extra electrons on it. The extra electrons will be located
a. only on the outside surface of the sphere.
b. only on the inside surface of the sphere.
c. both on the inside and outside surfaces of the sphere.
____
58. The electric field outside a Van de Graaff generator may be enormous, while inside the spherical dome, the electric field is
a. even more enormous.
b. almost as enormous.
c. zero.
____
59. A woman's hair stands out when she is in contact with a charged Van de Graaff generator. The reason her hair stands out is
because
a. hair strands are at a high voltage.
b. she is in a strong electric field.
c. like charges repel.
d. hair is a good conductor.
____
60. A Van de Graaff generator is a machine that
a. generates light.
b. works like a motor.
c. generates AC electricity.
d. builds up high voltages.
e. none of the above
____
61. After you rub a balloon on your hair, the balloon will likely be charged
a. to less than 10 volts.
b. to several hundred volts.
c. to several thousand volts.
d. not at all.
____
62. The electric field around an isolated electron has a certain strength 1 cm from the electron. The electric field strength 2 cm
from the electron is
a. half as much.
b. the same.
c. twice as much.
d. four times as much.
e. none of the above
____
63. A beam of electrons accelerates from the back of your TV set to the screen. In order to make the beam hit the top of the
screen, charged parallel plates create a vertical electric field. How will the top plate be charged?
a. negatively
b. positively
____
64. Two parallel plates are oppositely charged. The left plate is negative and the right plate is positive. In which direction does
the electric field point?
a.
b.
to the left
to the right
____
65. The electric field lines between two charges curve in space. The direction at a particular point on a curved line is the
direction of the
a. strongest field.
b. average straight line joining the charges.
c. resultant vector of the fields of the two charges at that point.
d. none of the above
____
66. Electrical potential energy per charge is electric
a. force.
b. power.
c. potential.
d. work.
____
67. Electric field lines between two oppositely charged parallel metal plates will be
a. straight lines, randomly spaced.
b. straight lines, evenly spaced.
c. curved lines grouped together in small bunches.
d. curved lines, evenly spaced.
e. curved lines, randomly spaced.
____
68. The electric field inside an uncharged metal ball is zero. If the ball gains a negative charge, the electric field inside the ball
will be
a. greater than zero.
b. less than zero.
c. zero.
____
69. A 2-C charge experiences a force of 40 N when put at a certain location in space. The electric field at that location is
a. 2 N/C.
b. 20 N/C.
c. 30 N/C.
d. 40 N/C.
e. 60 N/C.
____
70. The electric field in a certain region of space is 30 N/C. What is the force on a 2-C charge placed in that region?
a. 15 N
b. 2 N
c. 30 N
d. 4 N
e. 60 N
____
71. A 5-C charge is located near a positively charged sphere so that it has 50 J of electric potential energy. Its electric potential
is
a. 2 V.
b. 5 V.
c. 10 V.
d. 20 V.
e. 250 V.
____
72. If you use 20 J of work to push a 2-C charge into an electric field, its voltage with respect to its starting position is
a. 10 V.
b. less than 10 V.
c. more then 10 V.
____
73. If you use 17 J of work to push a charge into an electric field and then release the charge, as the charge flies past its starting
position, its kinetic energy is
a. more than 17 J.
b.
c.
less than 17 J.
17 J.
____
74. The electrical force on a 2-C charge is 20 N. What is the value of the electric field at the location of the charge?
a. 2 N/C
b. 10 N/C
c. 20 N/C
d. 40 N/C
e. 80 N/C
____
75. An electron is pushed into an electric field where it acquires a 7.0-V electric potential. If two electrons are pushed the same
distance into the same electric field, the electric potential of the two electrons is
a. 1.8 V.
b. 3.5 V.
c. 7.0 V.
d. 14.0 V.
e. 28.0 V.
____
76. In order for there to be a flow of charge from one place to another, there must be a
a. conductor, such as a wire, connecting the two places.
b. potential difference between the two places.
c. Both A and B above
____
77. In solid conductors, electric current is the flow of
a. positive and negative charges.
b. electrons.
c. negative ions.
d. protons.
e. none of the above
____
78. Electrons move in an electric circuit
a. by being bumped by other electrons.
b. by interacting with an established electric field.
c. by colliding with molecules.
d. because the wires are so thin.
e. none of the above
____
79. An ampere is a
a. unit of resistance.
b. unit of current.
c. type of charge.
d. voltage.
e. current.
____
80. An example of a voltage source is
a. a dry cell.
b. a generator.
c. a car battery.
d. rubbing a rubber rod with fur.
e. all of the above
____
81. Electrical resistance in a wire depends on the wire's
a. thickness.
b. conductivity.
c. length.
d. all of the above
e. none of the above
____
82. Compared to thin wires, electrical resistance in thick wires is
a.
b.
c.
less.
the same.
greater.
____
83. For most conductors, as their temperature increases, their resistance
a. decreases.
b. increases.
c. stays the same.
____
84. Electrical resistance is measured in
a. volts.
b. joules.
c. watts.
d. amperes.
e. none of the above
____
85. A woman experiences an electric shock. The electrons making the shock come from
a. the ground.
b. the electric field in the air.
c. a nearby power supply.
d. the woman's body.
e. the object causing the shock.
____
86. A pulsating electric field can travel through a wire at a speed of
a. less than 1 cm/s.
b. about 100 cm/s.
c. the speed of sound waves in metal.
d. nearly the speed of light.
____
87. A wire carrying a current is normally charged
a. not at all.
b. positively.
c. negatively.
____
88. While you are standing on the ground in your running shoes, the greatest resistance between you and the ground is in
a. your muscles.
b. your legs.
c. the clothes you are wearing.
d. your skin.
e. the running shoes.
____
89. The primary reason a bird can perch harmlessly on bare high voltage wires is that
a. a bird's feet are close together.
b. a bird has a very large electrical resistance.
c. there is no potential difference across the bird's feet.
d. all of the above
____
90. Alternating current is made by
a. alternating current and voltage.
b. alternating the direction of voltage of the power source.
c. huge chemical batteries.
d. none of the above
____
91. The frequency of AC current in North America is
a. 120 V.
b. 50 hertz.
c. 30 V.
d. 60 hertz.
____
92. Current from a battery is always
a. DC.
b. AC.
____
93. The net speed of electrons in a wire is about
a. 0.01 cm/s.
b. 10 m/s.
c. 100 kilometers per hour.
d. a few million kilometers per hour.
e. the speed of light.
____
94. Where do the electrons come from that produce heat and light in a light bulb?
a. the power company
b. the air
c. the wall plug
d. the bulb's wire filament
e. none of the above
____
95. In 2004, the number of electrons delivered to an average American home by an average power utility was
a. zero.
b. 110.
c. 220.
d. billions of billions.
e. none of the above
____
96. When we say an appliance uses up electricity, we really are saying that
a. electrons are taken out of the circuit and put somewhere else.
b. electron kinetic energy is changed into heat and other forms of energy.
c. the main power supply voltage is lowered.
d. current disappears.
e. electric charges are dissipated.
____
97. If you plug an electric toaster rated at 110 V into a 220-V outlet, current in the toaster will be
a. twice what it should be.
b. the same as if it were plugged into 110 V.
c. half what it should be.
d. more than twice what it should be.
e. none of the above
____
98. The resistance of your dry skin is usually around
a. 0.001 ohm.
b. 1 ohm.
c. 100 ohms.
d. 100,000 ohms.
e. millions of ohms.
____
99. Electric power is defined as
a. current times voltage.
b. current divided by voltage.
c. current times resistance.
d. resistance times voltage.
e. voltage divided by current.
____ 100. Compared to the filament thickness on a 60-W light bulb, the filament thickness of a 100-W light bulb will be
a. less.
b. the same.
c. greater.
____ 101. Power outlets in our homes typically have a potential difference of
a.
b.
c.
d.
e.
30 V.
120 A.
60 A.
240 V.
120 V.
____ 102. When an 8-V battery is connected to a resistor, 2 A of current flows in the resistor. What is the resistor's value?
a. 2 ohms
b. 4 ohms
c. 8 ohms
d. 16 ohms
e. more than 16 ohms
____ 103. The current through a 5-ohm resistor connected to a 150-V power supply is
a. 1A.
b. 10 A.
c. 30 A.
d. 150 A.
e. none of the above
____ 104. A 15-ohm resistor has a 5-A current in it. What is the voltage across the resistor?
a. 5 V
b. 15 V
c. 20 V
d. 25 V
e. more than 25 V
____ 105. What is the resistance of a toaster that uses 5 A of current when connected to a 120-volt power source?
a. 5 ohms
b. 24 ohms
c. 120 ohms
d. 600 ohms
e. none of the above
____ 106. When connected to a 110-volt power supply, how much current is in a light bulb that has a resistance of 220 ohms?
a. 0.5 A
b. 2.0 A
c. 110 A
d. 220 A
e. 24,200 A
____ 107. If you accidentally grabbed the prongs of a partially plugged-in 120-V electrical plug on a day when your skin resistance
was 130,000 ohms, how much current would pass through your body?
a. 0.0009 A
b. 120 A
c. 1,083 A
d. 130,000 A
e. 15,600,000 A
____ 108. How much power is used by a 12.0-V car battery that draws 0.5 A of current?
a. 0.5 W
b. 6 W
c. 12 W
d. 24 W
e. 30 W
____ 109. When plugged into a 120-V wall outlet, how much current is used by an electric blanket rated at 140 W?
a. 16,800 A
b. 140 A
c.
d.
e.
120 A
1.2 A
none of the above
____ 110. A 120-watt light bulb is connected to a 120-V outlet. How much current is in the light bulb?
a. 0.5 A
b. 1 A
c. 2 A
d. 6 A
e. more than 6 A
____ 111. A light bulb is plugged into a 120-volt outlet and has a 0.7 A current in it. What is the power rating of the light bulb?
a. 12 W
b. 17 W
c. 84 W
d. 120 W
e. 171 W
____ 112. A 60-W light bulb and a 100-W light bulb are both rated at 120 V. Which light bulb has the larger resistance?
a. the 60-W bulb
b. the 100-W bulb
c. Both have the same resistance.
____ 113. A 60-W light bulb and a 100-W light bulb are each connected to a 120-V outlet. Which light bulb has more current in it?
a. the 60-W bulb.
b. the 100-W bulb.
c. The same amount of current flows in both.
____ 114. An electric heater is rated at 300 W for use in a 110-V circuit. The circuit breaker in the circuit can handle 12 A of current.
How many heaters can be safely operated in the circuit?
a. 2
b. 3
c. 4
d. 5
e. more than 5
____ 115. A heater uses 21 A when connected to a 110-V line. If electric power costs 10 cents per kilowatt-hour in this location, the
cost of running the heater for 13 hours is _____.
a. $0.30
b. $0.75
c. $3.00
d. $7.51
e. none of the above
____ 116. A power line with a resistance of 9 ohms has a current of 80 A in it. The power dissipated in the line is
a. 360 W.
b. 720 W.
c. 1,440 W.
d. 57,600 W.
e. none of the above
True/False - Indicate whether the sentence or statement is true or false.
____ 117. The study of electricity at rest is electrostatics.
____ 118. Electrical forces are strong, but in comparison, gravitational forces are stronger.
____ 119. The reason electrons are attracted to protons is that electrons and protons have the same amount of charge.
____ 120. All electrons are identical; all have exactly the same mass and charge.
____ 121. The total amount of charge in the universe is constant. We have never observed a case of net creation or destruction of
charge.
____ 122. Coulomb's law says that there are two kinds of charges, positive and negative.
____ 123. Coulomb's law for electrical charges has the same mathematical form as Newton's law of gravitation.
____ 124. A material is a good insulator if outer electrons of atoms in the material are free to roam around.
____ 125. A material that is a good insulator of electricity is normally a poor conductor of electricity.
____ 126. Semiconductors can be made to conduct electricity and they can also be made to act like good insulators.
____ 127. When an object is charged by contact, electrons flow from the ground onto the object, or from the object onto the ground.
____ 128. When we allow charges to move onto or off a conductor by touching it with something connected to Earth, it is common to
say that we are grounding it.
____ 129. A bolt of lightning is a result of charging by induction.
____ 130. An atom that is electrically polarized vibrates in only one direction.
____ 131. When a charge is placed in a region of space where there is an electric field, the charge will experience a force.
____ 132. The direction of lines of force shows how large a force will be on a charge placed in an electric field.
____ 133. Even though a car may be struck by lightning, people inside the car will normally be safe.
____ 134. The energy a charge possesses by virtue of its location is called electrical potential energy.
____ 135. The unit of electric potential is the joule.
____ 136. Charge will move in a conductor when there is a difference in potential between the ends of the conductor.
____ 137. Charge flows from low potential to high potential.
____ 138. In solid conductors, positive current is the flow of protons in the conductor.
____ 139. The unit of electric current is the ampere.
____ 140. A voltage source is something that separates charges in a useful way.
____ 141. A resistor is something placed in a circuit that totally blocks the flow of electrons.
____ 142. Ohm's law is a relationship among voltage, current, and charge.
____ 143. You can feel a slight shock from a 12-volt battery if your skin is moist.
____ 144. You should never work with plugged-in electrical appliances while standing in water.
____ 145. Most of the electricity we buy through power companies is direct current.
____ 146. When you turn on a light, electrons move at speeds near the speed of light in order to light up the light bulb.
____ 147. Electrical outlets in our walls are a source of electrons to run electrical appliances.
____ 148. When charge moves in a circuit, it normally heats part of the circuit.
____ 149. The kilowatt-hour is a unit of power used by power companies.
Essay
150. State Coulomb's law. Explain what each symbol in it stands for, and use it to find the force between a 0.002-C charge and
a 0.006-C charge that are 10 meters apart.
151. List the similarities and differences between Coulomb's law and Newton's law of gravitation.
152. Calculate the electrical force between two electrons that are located on opposite sides of an ionized hydrogen atom. Use the
following values for the distance and charge size.
distance =
electron charge =
153. What is the difference between an insulator and a conductor? Which would you guess copper is? Wood? Distilled water?
154. Why should you not stand or sit in water when using electrical appliances? Why is it not a good idea to talk to your friend
on the phone while sitting in a bath?
155. What are three ways an object can become charged? How does each work? Give examples.
156. How is an electric field similar to a gravitational field? If you put a charged object in an electric field, what will happen to
it? In which direction will it move?
157. What are electric field lines? What do they show? How can they show the strength of an electric field?
158. How is electric potential energy similar to gravitational potential energy? How is it different? Where will an electron bound
in an atom have the largest electrical potential energy?
159. How is electrical potential different from electrical potential energy? What is its unit?
160. In Figure 33.17 on page 528, why does the hair on the woman's head stand out? Even though she is charged to a very high
voltage, she is unharmed. Explain.
161. What is the definition of electric current? How does it apply to a wire? How fast are electrons normally moving? On the
average, estimate how far they progress in 1 second. Explain why there is a difference between their actual speed and their
net speed.
162. What is electrical resistance? What characteristics of a wire determine its resistance? How does resistance normally vary
with temperature?
163. On an average day, estimate how much sustained voltage would you have to experience to feel a shock. What are some
good safety measures when working around power tools and electrical appliances?
164. What is the difference between direct current and alternating current? When we plug a light bulb into a wall outlet, where
do the electrons come from?
165. Suppose energy costs $0.09 per kilowatt-hour. How much would it cost to keep a 40-watt porch light on all night every
night for one month? (The average month is 30 days, and the average night is 10 hours.)
Problem
166. 100,000 electrons are removed from a neutral plastic ball. What is its charge?
167. 100 electrons are added to a neutral plastic ball. What is its charge?
168. What is the magnitude of the force on an electron in an electric field of 400 N/C?
169. 48 J of work are done to push 0.1 C of charge from point A to point B in an electric field. What is the voltage difference
between points A and B?
170. How much voltage is required to make 4 amperes flow through a 12-ohm resistor?
171. A battery does 18 J of work on 10 coulombs of charge. What voltage does the battery supply?
172. What is the current in a 60-W bulb connected to a 120-V source?
173. What is the power dissipated by a toaster that has a resistance of 40 ohms and is plugged into a 120-V outlet?
174. A certain bulb with a resistance of 240 ohms is labeled 60 W. For what voltage circuit was this bulb designed?
Physics Exam – Electricity Answer Section
MULTIPLE CHOICE
1. ANS: B
DIF:
2. ANS: E
DIF:
3. ANS: B
DIF:
4. ANS: A
DIF:
5. ANS: A
DIF:
6. ANS: B
DIF:
7. ANS: C
DIF:
8. ANS: D
DIF:
9. ANS: D
DIF:
10. ANS: B
DIF:
11. ANS: B
DIF:
12. ANS: E
DIF:
13. ANS: C
DIF:
14. ANS: D
DIF:
15. ANS: B
DIF:
16. ANS: B
DIF:
17. ANS: D
DIF:
18. ANS: D
DIF:
19. ANS: D
DIF:
20. ANS: A
DIF:
21. ANS: E
DIF:
22. ANS: D
DIF:
23. ANS: A
DIF:
24. ANS: C
DIF:
25. ANS: C
DIF:
26. ANS: A
DIF:
27. ANS: A
DIF:
28. ANS: C
DIF:
29. ANS: D
DIF:
30. ANS: B
DIF:
31. ANS: A
DIF:
32. ANS: B
DIF:
33. ANS: A
DIF:
34. ANS: C
DIF:
35. ANS: A
DIF:
36. ANS: B
DIF:
37. ANS: C
DIF:
38. ANS: C
DIF:
39. ANS: D
DIF:
40. ANS: E
DIF:
41. ANS: D
DIF:
42. ANS: E
DIF:
43. ANS: B
DIF:
44. ANS: C
DIF:
45. ANS: B
DIF:
46. ANS: C
DIF:
47. ANS: C
DIF:
48. ANS: A
DIF:
49. ANS: B
DIF:
50. ANS: B
DIF:
51. ANS: B
DIF:
52. ANS: C
DIF:
53. ANS: C
DIF:
54. ANS: B
DIF:
55. ANS: B
DIF:
56. ANS: B
DIF:
57. ANS: A
DIF:
58. ANS: C
DIF:
59. ANS: C
DIF:
60. ANS: D
DIF:
61. ANS: C
DIF:
62. ANS: E
DIF:
63. ANS: B
DIF:
64. ANS: A
DIF:
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p. 524
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p. 528
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p. 528
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p. 527
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p. 525
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p. 519
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p. 519
OBJ:
32.1
32.1
32.1
32.1
32.3
32.3
32.3
32.3
32.3
32.2
32.2
32.2
32.5
32.2
32.3
32.3
32.4
32.4
32.4
32.4
32.4
32.6
32.6
32.6
32.7
32.7
32.7
32.7
32.3
32.3
32.3
32.3
32.3
32.3
32.3
32.3
32.3
32.3
32.3
33.1
33.1
33.1
33.2
33.3
33.3
33.4
33.4
33.4
33.5
33.5
33.7
33.7
33.7
33.7
33.5
33.2
33.2
33.2
65.
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C
C
B
C
B
E
C
A
C
B
C
C
B
B
B
E
D
A
B
E
D
C
A
E
C
B
D
A
A
D
A
B
A
D
A
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2
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p. 519
p. 524
p. 519
p. 522
p. 518
p. 518
p. 524
p. 524
p. 523
p. 518
p. 524
p. 531
p. 532
p. 541
p. 533
p. 533
p. 534
p. 534
p. 534
p. 534
p. 543
p. 542
p. 541
p. 534
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p. 539
p. 539
p. 539
p. 541
p. 543
p. 543
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p. 535
p. 537
p. 543
p. 534
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p. 535
p. 535
p. 535
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p. 535
p. 535, p. 537
p. 543
p. 543
p. 543
p. 543
p. 543
p. 543
p. 543
p. 543, p. 544
p. 543
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33.2
33.5
33.2
33.3
33.1
33.1
33.5
33.5
33.4
33.1
33.5
34.1
34.2
34.9
34.2
34.3
34.4
34.4
34.4
34.4
34.10
34.9
34.9
34.4
34.6
34.7
34.7
34.7
34.9
34.10
34.10
34.10
34.5
34.6
34.11
34.4
34.7
34.5
34.5
34.5
34.5
34.5
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
34.11
34.11
34.11
34.11
34.11
34.11
34.11
OBJ:
34.11
TRUE/FALSE
117. ANS:
118. ANS:
119. ANS:
120. ANS:
121. ANS:
122. ANS:
123. ANS:
124. ANS:
125. ANS:
126. ANS:
127. ANS:
128. ANS:
T
F
F
T
T
F
T
F
T
T
F
T
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
1
2
1
1
1
2
2
1
2
1
2
1
REF:
REF:
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REF:
p. 500
p. 505
p. 501
p. 501
p. 504
p. 505
p. 505
p. 508
p. 508
p. 509
p. 509
p. 511
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
32.1
32.3
32.1
32.1
32.2
32.3
32.3
32.4
32.4
32.4
32.5
32.6
129.
130.
131.
132.
133.
134.
135.
136.
137.
138.
139.
140.
141.
142.
143.
144.
145.
146.
147.
148.
149.
ANS:
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T
F
T
F
T
T
F
T
F
F
T
T
F
F
T
T
F
F
F
T
F
DIF:
DIF:
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2
2
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1
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1
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2
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p. 512
p. 512
p. 518
p. 519
p. 521
p. 523
p. 524
p. 533
p. 534
p. 533
p. 533
p. 533
p. 534
p. 535
p. 537
p. 538
p. 539
p. 541
p. 543
p. 534
p. 543, p. 544
OBJ:
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32.6
32.7
33.1
33.2
33.3
33.4
33.5
34.3
34.3
34.2
34.2
34.3
34.4
34.5
34.6
34.6
34.7
34.9
34.10
34.4
ESSAY
150. The force between two charges depends directly on the magnitude of each charge and inversely on the square of the distance between the
charges.
, where k (
) is the proportionality constant, q1 and q2 are the magnitudes of the charges, d is the
distance between the charges, and F is the force between the charges.
DIF:
3
REF:
p. 505
OBJ:
32.3
151. Both inverse-square laws; both directly dependent on quantities involved; electric charge for electrical force, and mass for gravitational
force. Coulomb force is about 1039 times stronger than gravitational force. Electrical force either attractive or repulsive.
DIF:
3
REF: p. 515
OBJ: 32.3
152.
DIF:
3
REF:
p. 505
OBJ:
32.3
153. Good electrical conductor - material composed of atoms with "loose" outer electrons free to move around in the material, such as copper,
silver, aluminum. Good electrical insulator - material composed of atoms that tightly bind electrons such as glass, distilled water are
examples of good electrical insulators.
DIF:
3
REF: p. 508, p. 509
OBJ: 32.4
154. Ordinary water is a conductor. When using a plugged-in electrical device, do not stand or sit in water that is connected to Earth. If a short
circuit occurs, you may be part of the pathway to the ground. For the same reason it is not a good idea to use a connected phone while
taking a bath (although the voltage and current in a phone are relatively low).
DIF:
3
REF: p. 508
OBJ: 32.4
155. Objects can become charged by friction, contact or induction. Friction - two objects are rubbed together, thereby transferring electrons
from one object to the other. Contact - charge is directly transferred from one object to another object. Induction - one object is
momentarily grounded while a charged object is located nearby. Rubbing a rubber rod with fur is an example of charging by friction.
Touching the charged rubber rod to an uncharged tin can is an example of charging by contact. Holding a charged rod near a tin can and
touching the can with your finger is an example of charging by induction.
DIF:
3
REF: p. 514
OBJ: 32.5, 32.6, 32.7
156. Electric field similar to gravitational field - each exerts a force on objects located in the field. Strength of the force determined by the
field strength, and the direction of a force on a positive charge in the field is the same as the direction of the field. Both electrical and
gravitational fields obey inverse-square laws and both are dependent on the quantities involved. A positively charged particle will be
accelerated in the same direction as an electric field, and a negative particle will be accelerated in the opposite direction.
DIF:
3
REF: p. 517, p. 518
OBJ: 33.1
157. Electric field lines are lines that map and describe an electric field. They show the shape of the field and relative field strengths at various
points in space. About isolated point charges, field lines are oriented radially from the charges. They point outward about a positive
charge and inward about a negative charge. A positive test charge placed in the field will move in the direction of the field, whereas a
negative charge will move in a direction opposite to the field direction. Relative field strength is shown by the relative number of lines in
a volume of space.
DIF:
3
REF: p. 519
OBJ: 33.2
158. Electric and gravitational potential energies are both energies of position—they both depend on the location of charges or masses. They
are different in that electrical potential energy depends on charge and gravitational potential energy depends on mass. An electron far
from the nucleus will have the largest potential energy.
DIF:
3
REF: p. 523, p. 524
OBJ: 33.4
159. Electrical potential is electric potential energy per unit charge. Measured in volts.
DIF:
3
REF: p. 524
OBJ: 33.5
160. The hair on the woman's head stands out because she has excess electrons on her body. Since electrons repel each other, they will try to
get as far away from each other as possible. The result is that the electrons travel to the "corners" of the woman and enough are present
on her hair to make the hairs on her head stand out. Actually electrons are everywhere on the outside of the woman. The hair on her
hands, arms, and legs also stands out. The woman is unharmed because she is insulated from the ground and her entire body is at the
same high potential.
DIF:
3
REF: p. 528
OBJ: 33.7
161. Electric - rate of flow of electric charge in a circuit. In a wire, current is the flow of electrons through the wire. Electrons move at
extremely high speeds about the atomic nucleus and through empty space. But in a wire or other conductor they have so many collisions
each second that their overall headway is only about 0.01 cm/s.
DIF:
3
REF: p. 541, p. 542, p. 543
OBJ: 34.9, 34.10
162. Electrical resistance - resistance a conductor offers to the general movement of electrons. Depends on what material the wire is made of
as well as the dimensions of the wire. Resistance increases with temperature.
DIF:
3
REF: p. 534, p. 535
OBJ: 34.4
163. Assuming a body resistance of 100,000 ohms, you would have to be exposed to about 100 V to feel a shock. Good safety measures when
working around electricity are to turn off circuits while working on them, to wear well-insulated shoes, and to work with only one hand
so your heart is not in the path of an accidental circuit that includes you.
DIF:
3
REF: p. 537, p. 538
OBJ: 34.6
164. ANS:
In a direct-current circuit the polarity of the source never changes, whereas in an alternating-current circuit the source polarity changes at
a fixed rate, typically 60 times per second. When we plug a light bulb into the wall outlet, the electrons that actually cause light and heat
to be emitted are already in the bulb itself. The power company supplies energy; we supply the electrons!
DIF:
3
REF:
p. 539, p. 539
OBJ:
34.7
165. 30 days
10 hours/day = 300 hours in a month. The light would cost 0.040 kW x 300 hr x $0.09 / kw·hr = $1.08
DIF:
3
REF: p. 543, p. 544
OBJ: 34.11
PROBLEM
166.
167.
168.
169.
170.
171.
172.
173.
174.
1.6 x 10-14 C
-1.6 x 10-17 C
6.4 x 1017 N
480 V DIF:
48 V
DIF:
1.8 V DIF:
0.5 A DIF:
360 W DIF:
120 V DIF:
DIF:
DIF:
DIF:
3
2
3
2
3
3
3
3
3
REF:
REF:
REF:
REF:
REF:
REF: p. 525
REF: p. 525
REF: p. 518
p. 524 OBJ:
p. 535 OBJ:
p. 533, p. 534
p. 543 OBJ:
p. 543 OBJ:
OBJ:
OBJ:
OBJ:
33.5
34.5
REF:
p. 543 OBJ:
34.11
33.5
33.5
33.1
OBJ:
34.11
34.11
34.3