Chapter 6 Electricity and Magnetism

A car's storage battery is being charged at a rate of 75 W. If the potential difference across the battery's terminals is 13.6 V, charge is being transferred between its plates at a. 0.18 C/s b. 2.8 C/s c. 5.5 C/s d. 1020 C/s

c

Five joules of work are needed to shift 10 C of charge from one place to another. The potential difference between the places is a. 0.5 V b. 2 V c. 5 V d. 10 V

A

A magnetic field does not interact with a a. stationary electric charge b. moving electric charge c. stationary magnet d. moving magnet

c

A moving electric charge produces a. only an electric field b. only a magnetic field c. both an electric and a magnetic field d. any of these, depending on its speed

c

Coulomb's law for the force between electric charges belongs in the same general category as a. the law of conservation of energy b. Newton's second law of motion c. Newton's law of gravitation d. the second law of thermodynamics

c

The electric energy lost when a current passes through a resistance a. becomes magnetic energy b. becomes potential energy c. becomes heat d. disappears completely

c

The resistance of a lightbulb that draws a current of 2 A when connected to a 12-V battery is a. 1.67 Ω b. 2 Ω c. 6 Ω d. 24 Ω

c

A 240-V, 1-kW electric heater is mistakenly connected to a 120-V power line that has a 15-A fuse. The heater will a. give off less than 1 kW of heat b. give off 1 kW of heat c. give off more than 1 kW of heat d. blow the fuse

a

A transformer can change a. the voltage of an alternating current b. the power of an alternating current c. alternating current to direct current d. direct current to alternating current

a

An electromagnet a. uses an electric current to produce a magnetic field b. uses a magnetic field to produce an electric current c. is a magnet that has an electric charge d. operates only on alternating current

a

Electric power is equal to a. (current)(voltage) b. current/voltage c. voltage/current d. (resistance)(voltage)

a

Superconductors a. have no electrical resistance b. have very little electrical resistance c. are used in making transistors d. have no practical applications

a

The current in a 40-W, 120-V electric lightbulb is a. 1/3A b. 3 A c. 80 A d. 4800 A

a

The particle easiest to remove from an atom is a (an) a. electron b. proton c. neutron d. nucleus

a

When a magnetized bar of iron is strongly heated, its magnetization a. becomes weaker b. becomes stronger c. reverses its direction d. is unchanged

a

Match each of the electrical qualities listed below with the appropriate unit from the list on the right: a. resistance volt b. current ampere c. potential difference ohm d. power watt

all

A positive electric charge a. attracts other positive charges b. repels other positive charges c. does not interact with other positive charges but only with negative ones d. consists of an excess of electrons

b

A solid conductor is one a. whose electrons are firmly bound in place b. whose electrons are free to move about c. that has no electrons d. that has too many electrons

b

A transformer whose primary coil has twice as many turns as its secondary coil is used to convert 240-V ac to 120-V ac. If the current in the secondary coil is 4 A, the primary current is a. 1 A b. 2 A c. 4 A d. 8 A

b

An object has a positive electric charge whenever a. it has an excess of electrons b. it has a deficiency of electrons c. the nuclei of its atoms are positively charged d. the electrons of its atoms are positively charged

b

If 105 electrons are added to a neutral object, its charge will be a. −1.6 × 10−24 C b. −1.6 × 10−14 C c. +1.6 × 10−24 C d. +1.6 × 10−14 C

b

In a drawing of magnetic field lines, the weaker the field is, the a. closer together the field lines are b. farther apart the field lines are c. more nearly parallel the field lines are d. more divergent the field lines are

b

Magnetic field lines provide a convenient way to visualize a magnetic field. Which of the following statements is not true? a. The path followed by an iron particle released near a magnet corresponds to a field line. b. The path followed by an electric charge released near a magnet corresponds to a field line. c. A compass needle in a magnetic field turns until it is parallel to the field lines around it. d. Magnetic field lines do not actually exist.

b

Protons and electrons have different masses. When they are the same distance apart, the electric force between two electrons a. is less than the force between two protons b. is the same as the magnitude of the force between two protons c. is greater than the force between two protons d. Any of these choices could be correct, depending on the distance between each pair of particles.

b

The alternating current in the secondary coil of a transformer is induced by a. the varying electric field of the primary coil b. the varying magnetic field of the primary coil c. the varying magnetic field of the secondary coil d. the iron core of the transformer

b

The magnetic field shown in Fig. 6-50 is produced by Figure 6-50 a. two north poles b. two south poles c. a north pole and a south pole d. a south pole and an unmagnetized iron bar

b

The nature of the force that is responsible for the operation of an electric motor is a. electric b. magnetic c. a combination of electric and magnetic d. either electric or magnetic, depending on the design of the motor

b

When the voltage across a certain resistance is V, the power delivered is P. If the voltage is doubled to 2V, the power delivered becomes a. 2P b. 4P c. P2 d. 4P2

b

The electric force between a proton and an electron a. is weaker than the gravitational force between them b. is equal in strength to the gravitational force between them c. is stronger than the gravitational force between them d. is any of these, depending on the distance between the proton and the electron

c

The magnetic field lines around a long, straight current-carrying wire are a. straight lines parallel to the current b. straight lines that radiate from the current like spokes of a wheel c. concentric circles around the current d. concentric helixes around the current

c

The magnetic field of a bar magnet resembles most closely the magnetic field of a. a straight wire carrying a direct current b. a straight wire carrying an alternating current c. a wire loop carrying a direct current d. a wire loop carrying an alternating current

c

A 120-V, 1-kW electric heater is mistakenly connected to a 240-V power line that has a 15-A fuse. The heater will a. give off less than 1 kW of heat b. give off 1 kW of heat c. give off more than 1 kW of heat d. blow the fuse

d

A current-carrying wire is in a magnetic field with the direction of the current the same as that of the field. a. The wire tends to move parallel to the field. b. The wire tends to move perpendicular to the field. c. The wire tends to turn until it is perpendicular to the field. d. The wire has no tendency to move or to turn.

d

A generator is said to "generate electricity." What it actually does is act as a source of a. electric charge b. electrons c. magnetism d. electric energy

d

A positive and a negative charge are initially 4 cm apart. When they are moved closer together so that they are now only 1 cm apart, the force between them is a. 4 times smaller than before b. 4 times larger than before c. 8 times larger than before d. 16 times larger than before

d

A positively charged rod is brought near an isolated metal ball. Which of the sketches in Fig. 6-49 best illustrates the arrangement of charges on the ball? Figure 6-49 a. (a) b. (b) c. (c) d. (d)

d

All magnetic fields originate in a. iron atoms b. permanent magnets c. stationary electric charges d. moving electric charges

d

An atom consists of a a. uniform distribution of positive charge in which electrons are embedded b. uniform distribution of negative charge in which electrons are embedded c. small negative nucleus surrounded at a distance by protons d. small positive nucleus surrounded at a distance by electrons

d

The charge on an electron a. is 1 C b. depends on the electron's mass c. depends on the electron's sizeterm-2 d. is always the same

d

The force between two charges of −3 × 10−9 C that are 5 cm apart is a. 1.8 × 10−16 N b. 3.6 × 10−15 N c. 1.6 × 10−6 N d. 3.2 × 10−5 N

d

The force on an electron that moves in a curved path must be a. gravitational b. electrical c. magnetic d. one or more of these

d

The voltage needed to produce a current of 5 A in a resistance of 40 Ω is a. 0.125 V b. 5 V c. 8 V d. 200 V

d