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Chapter 23

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# Chapter 23 - PowerPoint PPT Presentation

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.

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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.
• electrons.
• protons.
• ions.
• All or any of these.
• 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.
• current.
• resistance.
• Both of these.
• None of these.
• 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).

• Electric charges
• Electric current
• Electric field
• All of these.
• 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.
• near the speed of light.
• near the speed of sound.
• about a snail’s pace.
• imaginary.
• near the speed of light.
• near the speed of sound.
• about a snail’s pace.
• imaginary.
• remains unchanged if resistance remains constant.
• halves.
• doubles.
• quadruples.
• 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.
• Incandescent lamp
• Compact fluorescent lamp
• Light-emitting diode
• All about the same.
• 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.