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### Chapter 23

Electric Current

The flow of charge in an electric circuit is much

- like the flow of water in a system of pipes.
- different than water flow in pipes.
- like an electric valve.
- like an electric pump.

The flow of charge in an electric circuit is much

- like the flow of water in a system of pipes.
- different than water flow in pipes.
- like an electric valve.
- like an electric pump.

Electric charge will flow in an electric circuit when

- electrical resistance is low enough.
- a potential difference exists.
- the circuit is grounded.
- electrical devices in the circuit are not defective.

Electric charge will flow in an electric circuit when

- electrical resistance is low enough.
- a potential difference exists.
- the circuit is grounded.
- electrical devices in the circuit are not defective.

The electric current in a copper wire is normally composed of

- electrons.
- protons.
- ions.
- All or any of these.

The electric current in a copper wire is normally composed of

- electrons.
- protons.
- ions.
- 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?

- Voltage flows in a circuit.
- Charge flows in a circuit.
- A battery is the source of electrons in a circuit.
- All are correct.

Which statement is correct?

- Voltage flows in a circuit.
- Charge flows in a circuit.
- A battery is the source of electrons in a circuit.
- 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

- decreases.
- remains unchanged.
- increases.
- vanishes with enough heat.

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

- decreases.
- remains unchanged.
- increases.
- vanishes with enough heat.

The amount of current in a circuit depends on the

- voltage across the circuit.
- electrical resistance of the circuit.
- Both of these.
- None of these.

The amount of current in a circuit depends on the

- voltage across the circuit.
- electrical resistance of the circuit.
- Both of these.
- None of these.

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

- current.
- resistance.
- Both of these.
- None of these.

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

- current.
- resistance.
- Both of these.
- 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

- 5 A.
- 10 A.
- 132 A.
- 2420 A.

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

- 5 A.
- 10 A.
- 132 A.
- 2420 A.

To receive an electric shock there must be

- current in one direction.
- moisture in the electrical device being used.
- a difference in potential across part or all of the body.
- high voltage and low body resistance.

To receive an electric shock there must be

- current in one direction.
- moisture in the electrical device being used.
- a difference in potential across part or all of the body.
- high voltage and low body resistance.

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

- flow steadily in one direction only.
- flow in one direction only.
- steadily flow to and fro.
- flow to and fro.

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

- flow steadily in one direction only.
- flow in one direction only.
- steadily flow to and fro.
- flow to and fro.

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

- Diode
- Capacitor
- Both of these.
- None of these.

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

- Diode
- Capacitor
- Both of these.
- 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?

- Electric charges
- Electric current
- Electric field
- All of these.

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

- Electric charges
- Electric current
- Electric field
- 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

- must be supplied by you, just as water must be supplied for a water pipe.
- are already in the wire.
- may fall out, which is why wires are insulated.
- None of these.

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

- must be supplied by you, just as water must be supplied for a water pipe.
- are already in the wire.
- may fall out, which is why wires are insulated.
- None of these.

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

- near the speed of light.
- near the speed of sound.
- about a snail’s pace.
- imaginary.

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

- near the speed of light.
- near the speed of sound.
- about a snail’s pace.
- imaginary.

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

- remains unchanged if resistance remains constant.
- halves.
- doubles.
- quadruples.

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

- remains unchanged if resistance remains constant.
- halves.
- doubles.
- 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

- 10 W.
- 12 W.
- 120 W
- 1200 W.

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

- 10 W.
- 12 W.
- 120 W
- 1200 W.

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

- Incandescent lamp
- Compact fluorescent lamp
- Light-emitting diode
- All about the same.

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

- Incandescent lamp
- Compact fluorescent lamp
- Light-emitting diode
- 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

- half, 1 A.
- 2 A.
- dependent on internal battery resistance.
- 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

- half, 1 A.
- 2 A.
- dependent on internal battery resistance.
- 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

- half, 1 A.
- 2 A.
- more than 2 A.
- 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

- half, 1 A.
- 2 A.
- more than 2 A.
- 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

- operate fewer devices at the same time.
- change the wiring from parallel to series for troublesome devices.
- find a way to bypass the fuse or circuit breaker.
- All of these.

One way to prevent overloading in your home circuit is to

- operate fewer devices at the same time.
- change the wiring from parallel to series for troublesome devices.
- find a way to bypass the fuse or circuit breaker.
- All of these.

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