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Preparation for Physics Final > Chapter 34 > Flashcards

Chapter 34 Flashcards

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1
Q

Heat flows through a conductor when…

A

a difference in temperature exists between its ends

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2
Q

Heat flows from…

A

the end of higher temperature to the end of lower temperature.

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3
Q

When both ends reach the same temperature…

A

the flow of heat ceases

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4
Q

When the ends of an electric conductor are at different electric potentials…

A

charge flows from one end to the other

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5
Q

When does charge flow?

A

when there is a potential difference, or difference in porential (voltage), between the ends of a conductor

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6
Q

Until when will the flow of charge end?

A

when both ends reach a common potential

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7
Q

When there is no potential difference…

A

there is no longer a flow of charge through the conductor

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8
Q

To attain a sustained flow of charge in a conductor…

A

some arrangement must be provided to keep one end at a higher potential then the other. The situation is analogous to the flow of water from a higher reservoir to a lower one. Water will flow in a pipe that connects the reservoirs only as a difference in water level exists.

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9
Q

The flow of water in the pipe, like the flow of charge in the wire that connects the Van ge Graaff generator to the ground, will cease when…

A

the “pressures” at the two ends are equal

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10
Q

In order that the flow be sustained…

A

there must be a suitable pump of some sort to maintain a difference in water levels. Then there will be a continual difference in water pressures and a continual flow of water. The same is true of electric current

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11
Q

What is electric current?

A

The flow of electric charge

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12
Q

In solid conductors the electrons…

A

carry the charge through the circuit because they are free to move throughout the atomic network.

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13
Q

What are electrons in solid conductors called?

A

conduction electrons

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14
Q

What is electric currents charged in?

A

Amperes

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15
Q

Whats is an ampere?

A

The flow of 1 coulomb of charge per second

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16
Q

A current-carrying wire has a net electric charge of…

A

zero

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17
Q

While the current is flowing…

A

negative electrons swarm through the atomic network that is composed of positively charged atomic nuclei

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18
Q

When electrons flow in a wire…

A

the number entering one end is the same as the number leaving the other. So we see that the net charge of the wire is normally at every moment

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19
Q

Charges do not flow unless…

A

there is a potential difference

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20
Q

A sustained current requires a…

A

suitable “electric pump” to provide a sustained potential difference.

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21
Q

What is a voltage source?

A

Something that provides a potential difference

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22
Q

What happens if you charge a metal sphere positively and another negatively? Why is this not a good voltage source?

A

You can develop a large voltage between them. This is not a good voltage source b/c when spheres are connected by a conductorm the potentials equalizr in a single brief surge of moving charges

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23
Q

Voltage sources such as batteries and generators supply…

A

energy that allows charges to move steadily

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24
Q

In a battery a chemical reaction occuring inside releases…

A

electrical energy

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25
Q

Generators convert mechanical energy to…

A

electrical energy

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26
Q

The electrical potential energy produced by whatever means is available…

A

at the terminals of the battery or generator

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27
Q

The potential energy per coulomb of charge available to the electrons moving between terminals is the…

A

voltage

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28
Q

What does the voltage provide?

A

the 120 volts delivered to home outlets

29
Q

Water will flow through the pipe if…

A

there is a difference in pressure across sthe pipe or between its ends

30
Q

Does pressure flow?

A

No

31
Q

What does voltage cause?

A

Current

32
Q

What does the amount of charge that flows in a circuit depend on?

A

The voltage provided by the voltage source

33
Q

What does current also depend on?

A

electric resistance

34
Q

What is electric resistance?

A

The resistance that the conductor offers to the flow of charge

35
Q

The resistance of a wire depends on…

A

the conductivity of the material used in the wire (that is, how well it conducts) and also on the thickness and length of the wire.

36
Q

Thick wires have ________resistance than thin wires

A

less

37
Q

Longer wires have _______ resistance than short wires

A

more

38
Q

What does electric resistance depend on?

A

temperature

39
Q

The greater the jostinling about ofatoms within the conductor…

A

the greater resistance the conductor offers to the flow of charge

40
Q

For most conductors increased temperature means…

A

increased resistance

41
Q

When does the resistance of some materials become zero?

A

At very low temperatures,

42
Q

Superconductivity

A

The resistance of some materials becomes zero at very low temperatures, a phenomenon

43
Q

Do certain metals acquire superconductivity?

A

Yes

44
Q

Once electric current is stablished in a superconductor…

A

the electrons flow indefinitely

45
Q

Ohms

A

electric resistance is measured in units

46
Q

What is Ohm’s law?

A

The relationship among voltage, current, and resistance

47
Q

Ohm’s law states that the ______ in a circuit is ________proportional to the _______ impressed across the circuitm and is __________ proportional to the resistance of the circuit.

A

current; directly; voltage; inversely

48
Q

What is the formula for current?

A

current = voltage/resistance

49
Q

What is the formula for ampere?

A

1 ampere = 1 volt/ohm

50
Q

What is the source of electrons in a circuit?

A

the conducting circuit material itself

51
Q

Do electrons flow from the power utility through the power lines and into the wall outlets of their homes.

A

No

52
Q

The outlets in homes are…

A

AC

53
Q

Do electrons travel appreciable distances through a wire in an AC circuit.

A

No, they vibrate to and fro about relatively fixed positions

54
Q

When you plug a lamp into an AC outlet, what happend?

A

energy flows flows from teh outlet into the lamp, not electrons

55
Q

Energy is carried by…

A

the electric field and causes a vibratory motion of the electrons that already exist in the lamp filament

56
Q

If 120 volts AC are impressed on a lamp, then…

A

an average of 120 Jolues of wnergy are dissipated by each coulomb of charge that is made to vibrate.

57
Q

Most of this electrical energy appears as heat, while

A

some of it takes the form of light

58
Q

Do power utilies sell electrons?

A

No. they sell energy. you supply the electrons

59
Q

When you are jolted by an AC electric shock…

A

the electrons making up the current in your body originate from your body

60
Q

What comes out of the wire and through your body into the ground?

A

energy

61
Q

What does energy cause?

A

Free electrons in your body to vibrate in unison.

62
Q

Small vibrations __________; large vibrations can be _________

A

tingle; fatal

63
Q

Unless it is a superconductor…

A

a charge moving in a circuit expends energy. This may result in heating the circuit or in turning a motor

64
Q

What is electric power?

A

the rate at which electrical energy is converted into another form such as mechanical energy, heat, or light

65
Q

What is electric power equal to?

A

the product of current and voltage

66
Q

Formula for electric power

A

electric power = current x voltage

67
Q

If the voltage is expressed in volts and the current in amperes, then the power is expressed in watts. What’s the formula?

A

1 watt = (1 ampere) x (1 volt)

68
Q

If a lamp at 120 watts operates on a 120-volt line, you can see that it will draw a current of 1 amp. What’s the formula?

A

120 watts = 1 ampere x 120 volts
60 watts = 0.5 ampere x 120 volts

Preparation for Physics Final (11 decks)

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