Chapter 23

Electric Current

The flow of charge in an electric circuit is much

a. like the flow of water in a system of pipes.

b. different than water flow in pipes.

c. like an electric valve.

d. like an electric pump.

The flow of charge in an electric circuit is much

a. like the flow of water in a system of pipes.

b. different than water flow in pipes.

c. like an electric valve.

d. like an electric pump.

Electric charge will flow in an electric circuit when

a. electrical resistance is low enough.

b. a potential difference exists.

c. the circuit is grounded.

d. electrical devices in the circuit are not defective.

Electric charge will flow in an electric circuit when

a. electrical resistance is low enough.

b. a potential difference exists.

c. the circuit is grounded.

d. electrical devices in the circuit are not defective.

The electric current in a copper wire is normally composed of

a. electrons.

b. protons.

c. ions.

d. All or any of these.

The electric current in a copper wire is normally composed of

a. electrons.

b. protons.

c. ions.

d. All or any of these.

Explanation: Although current can consist of protons and ions, in a copper wire current consists of electrons appropriately called conduction electrons.

Which statement is correct?

a. Voltage flows in a circuit.

b. Charge flows in a circuit.

c. A battery is the source of electrons in a circuit.

d. All are correct.

Which statement is correct?

a. Voltage flows in a circuit.

b. Charge flows in a circuit.

c. A battery is the source of electrons in a circuit.

d. All are correct.

Explanation: Voltage causes the flow of electrons, and doesn’t flow. Charges flow. A battery is a source of energy, not electrons.

Apply heat to a copper wire and the resistance of the wire

a. decreases.

b. remains unchanged.

c. increases.

d. vanishes with enough heat.

Apply heat to a copper wire and the resistance of the wire

a. decreases.

b. remains unchanged.

c. increases.

d. vanishes with enough heat.

The amount of current in a circuit depends on the

a. voltage across the circuit.

b. electrical resistance of the circuit.

c. Both of these.

d. None of these.

The amount of current in a circuit depends on the

a. voltage across the circuit.

b. electrical resistance of the circuit.

c. Both of these.

d. None of these.

When you double the voltage in a simple electric circuit, you double the

a. current.

b. resistance.

c. Both of these.

d. None of these.

When you double the voltage in a simple electric circuit, you double the

a. current.

b. resistance.

c. Both of these.

d. None of these.

Explanation: This is straight-forward Ohm’s law. Current = voltage/resistance.

When 110 volts are impressed across a 22-ohm resistor, the current in the

resistor is

a. 5 A.

b. 10 A.

c. 132 A.

d. 2420 A.

When 110 volts are impressed across a 22-ohm resistor, the current in the resistor is

a. 5 A.

b. 10 A.

c. 132 A.

d. 2420 A.

To receive an electric shock there must be

a. current in one direction.

b. moisture in the electrical device being used.

c. a difference in potential across part or all of the body.

d. high voltage and low body resistance.

To receive an electric shock there must be

a. current in one direction.

b. moisture in the electrical device being used.

c. a difference in potential across part or all of the body.

d. high voltage and low body resistance.

The difference between dc and ac in electrical circuits is that in dc the electrons

a. flow steadily in one direction only.

b. flow in one direction only.

c. steadily flow to and fro.

d. flow to and fro.

The difference between dc and ac in electrical circuits is that in dc the electrons

a. flow steadily in one direction only.

b. flow in one direction only.

c. steadily flow to and fro.

d. flow to and fro.

Which device is used to convert ac to a fairly steady dc?

a. Diode

b. Capacitor

c. Both of these.

d. None of these.

Which device is used to convert ac to a fairly steady dc?

a. Diode

b. Capacitor

c. Both of these.

d. None of these.

Explanation: Although a diode will convert ac to dc, the additional use of a capacitor produces steadiness (as Figure 23.11 in the text shows).

What travels at about the speed of light in an electric circuit?

a. Electric charges

b. Electric current

c. Electric field

d. All of these.

What travels at about the speed of light in an electric circuit?

a. Electric charges

b. Electric current

c. Electric field

d. All of these.

Explanation: The electric field in a circuit travels at nearly the speed of light, not the electrons nor the current.

When you buy a water pipe in a hardware store, the water isn’t included. When you

buy copper wire, electrons

a. must be supplied by you, just as water must be supplied for a water pipe.

b. are already in the wire.

c. may fall out, which is why wires are insulated.

d. None of these.

When you buy a water pipe in a hardware store, the water isn’t included. When you

buy copper wire, electrons

a. must be supplied by you, just as water must be supplied for a water pipe.

b. are already in the wire.

c. may fall out, which is why wires are insulated.

d. None of these.

The drift speed of electrons that make up current in a circuit is

a. near the speed of light.

b. near the speed of sound.

c. about a snail’s pace.

d. imaginary.

The drift speed of electrons that make up current in a circuit is

a. near the speed of light.

b. near the speed of sound.

c. about a snail’s pace.

d. imaginary.

If you double both the current and the voltage in a circuit, the power

a. remains unchanged if resistance remains constant.

b. halves.

c. doubles.

d. quadruples.

If you double both the current and the voltage in a circuit, the power

a. remains unchanged if resistance remains constant.

b. halves.

c. doubles.

d. quadruples.

Explanation: Electric power = current voltage. Doubling both current and voltage corresponds to 4 times as much power.

A lamp with a current of 10 A connected to 120 volts consumes a

power of

a. 10 W.

b. 12 W.

c. 120 W

d. 1200 W.

A lamp with a current of 10 A connected to 120 volts consumes a

power of

a. 10 W.

b. 12 W.

c. 120 W

d. 1200 W.

Which of these lamps is the longer lasting in a common circuit?

a. Incandescent lamp

b. Compact fluorescent lamp

c. Light-emitting diode

d. All about the same.

Which of these lamps is the longer lasting in a common circuit?

a. Incandescent lamp

b. Compact fluorescent lamp

c. Light-emitting diode

d. All about the same.

Comment: More about LEDs in Chapter 30.

In a simple circuit consisting of a single lamp and a single battery, when current in the lamp is 2 amperes, the current in the

battery is

a. half, 1 A.

b. 2 A.

c. dependent on internal battery resistance.

d. Not enough information to say.

In a simple circuit consisting of a single lamp and a single battery, when current in the lamp is 2 amperes, the current in the

battery is

a. half, 1 A.

b. 2 A.

c. dependent on internal battery resistance.

d. Not enough information to say.

Comment: It is important to know that the current in the devices in series is also the current in the battery. Current will depend on battery resistance, but if there’s 2 A in the circuit, there’s 2 A in the battery!

In a circuit with two lamps in parallel, if the current in one lamp is 2 amperes,

the current in the battery is

a. half, 1 A.

b. 2 A.

c. more than 2 A.

d. Not enough information to say.

In a circuit with two lamps in parallel, if the current in one lamp is 2 amperes,

the current in the battery is

a. half, 1 A.

b. 2 A.

c. more than 2 A.

d. Not enough information to say.

Explanation: Current in the battery will be the sum of currents in the two branches.

One way to prevent overloading in your home circuit is to

a. operate fewer devices at the same time.

b. change the wiring from parallel to series for troublesome devices.

c. find a way to bypass the fuse or circuit breaker.

d. All of these.

One way to prevent overloading in your home circuit is to

a. operate fewer devices at the same time.

b. change the wiring from parallel to series for troublesome devices.

c. find a way to bypass the fuse or circuit breaker.

d. All of these.