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Preparation for Physics Final > Chapter 37 > Flashcards

Chapter 37 Flashcards

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1
Q

What did Farday and Henry discover?

A

Electric current can be produced in a wire by simply moving a magnett into or out of a wire coil. No battery or other voltage was needed

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2
Q

What was discovered about voltage.

A

That voltage was induced by the relative motion of a wire with respect to a magnetic field.

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3
Q

What does the production of voltage depend on?

A

The relative motion of the conductor with respect to the magnetic field

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4
Q

How is voltage induced?

A

When the magnetic field of a magnet moves past a stationary conductor, or the conductor moves through a stationary magnetic field as shown.

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5
Q

What does the amount of voltage induced depend on?

A

How quickly the magnetic field lines traversed by the wire.

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6
Q

What does very slow motion produce?

A

hardly any voltage at all.

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7
Q

What does quick motion induce?

A

A greater voltage

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8
Q

The greater the number of loops of wire that move in a magnetic field…

A

the greater are the induced voltage and the current in the wire

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9
Q

Why is work done in pushing in the magnet into the loop?

A

The induced current in the loop created a magnetic field that repels the approaching magnet

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10
Q

The force that you exert on the magnet multiplied by the distance that you move the magnet is your…

A

input work

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11
Q

What is the work equal to?

A

The energy expended (orpossibly stored) in the circuit to which the coil is connected.

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12
Q

What does the amount of voltage induced depend on?

A

On how quickly the magnetic field changes

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13
Q

Very slow movement of the magnet into the coil produces…

A

hardly any motion at all

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14
Q

What is electromagnetic induction?

A

the phenomenon of inducing voltage by changing the magnetic field around a conductor.

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15
Q

What is Faraday’s law?

A

The relationship between induced voltage and rate of change of a magnetic field

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16
Q

What does Faraday’s law state?

A

That the induced voltage in a coil is proportional to the product of the number of loops, the cross-sectional area of each loop, and the rate at which the magnetic field changes within those loops

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17
Q

What does the amount of currrent produced by electromagnetic induction depend on?

A

On the induced voltage and on the resistance of the soil and the circuit to which it is connected.

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18
Q

When you plunge a magnet in and out of a closed rubber loop and in and out of a closed loop of copper….

A

the voltage induced in each is the same, providing each intercepts the same number of magnetic field lines

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19
Q

What is one way to generate a current?

A

to plunge a magnet into and out of a coil of wire

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20
Q

As the magnetic field strength inside the coil is increased (magnet entering)….

A

the induced voltage in the coil is directed one way

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21
Q

When the magnetic field diminished (magnet leaving)….

A

the voltage is induced in the opposite direction

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22
Q

The greater the frequency of field change…

A

the greater the induced voltage

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23
Q

The frequency of the induced alternating voltage equals the…

A

frequency of the changing magnetic field within the loop

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24
Q

What is a generator?

A

A machine that produces electric current by rotating a coil within a stationary magnetic field

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25
Q

Whereas a ______ converts _________ energy into _________ energy, a _________ converts _________ energy into _________ energy.

A

motor; electrical; mechanical; generator; mechanical; electrical

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26
Q

When the loop of wire is rotated in the magnetic field…

A

there is a change in the number of magnetic field lines within the loop

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27
Q

As rotation continues….

A

the magnetic field inside the loop changes in cyclic fashion

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28
Q

The voltage induced by the generator _________, and the current produced is ____________ _________ (AC)

A

alternates; alernating; current

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29
Q

The current changed magnitude and direction __________

A

periodicaly

30
Q

What is required to operate a generator?

A

an energy source

31
Q

How do moving charges experience a force?

A

that is perpendicular to both their motion and the magnetic field they transverse

32
Q

We call the deflected wire the ________ effect?

A

motor

33
Q

We call the law of induction the _________ effect?

A

generator

34
Q

When does the motor effect occurs?

A

When a current moves through a magnetic field

35
Q

The wire is tugged with the…

A

electrons

36
Q

The electrons in this wore experience a force ___________ to their motion, which is along the wire.

A

perpendicular

37
Q

It is customary to refer to the coil connected to ther power source as the ___________; and the other ___________.

A

primary (input); secondary (output)

38
Q

As soon as the switch is closed in the primary and current passes through its coil….

A

a current occurs in the secondary also - even though there is no material connection between the two coils. Only a brief surge of current occurs in the secondary

39
Q

When the primary switch is opened…

A

a surge of cuurent again registers in the secindary but in the opposite direction

40
Q

When the magnetic field builds up around the primary extends into the secondary coil…

A

changes in the magnetic field of the primary are sensed by the nearby secondary. These changes of magnetic field within the primary is intensified by the alignment of magnetic domains in the iron

41
Q

Instead of opening and closing a switch to produce the change of magnetic field, supppose that alternating current is used to power the primary then…

A

the rate at which the magnetic field changes in the primary (and hence in the secondary) is equal to the frequency of the alternating current.

42
Q

What is a transformer?

A

A device for increasing or decreasing voltage through electromagnetic induction

43
Q

A transformer works by…

A

inducing a changing magnetic field in one coil, which induces an alternating current in a nearby second coil

44
Q

Voltages may be what with a transformer?

A

stepped up or stepped down

45
Q

If the secondary has fewer turnes than the primary, then the…

A

alternating voltage produced in the secondary will be lower than in the primary. The voltage is said to be stepped down.

46
Q

So _________ energy can be fed into the __________ at a given alternating voltage and taken from the ___________ at a greater or lower alternating voltage, depending on the relative number of turns in the primary and secondary coil windings.

A

electrical; primary; secondary

47
Q

primary voltage/number of primary turns = secondary voltage/number of secondary turns

A
48
Q

The transformer does what to the coils…

A

transfers energy from one coil to another

49
Q

What is power?

A

The rate at which energy is transferred

50
Q

(voltage x current)primary = (voltage x current)secondary

A
51
Q

Almost all energy sold in in the form of…

A

alternatinf current because of the ease with which it can be transformed from one voltage to another

52
Q

Power is transmitted ________ distances at _______ voltage and correspondingly ______ currents, a process that otherwise would result in _______energy losses owning to the heating of the wires

A

great; high; low; large

53
Q

How is energy transferred from one system of conducting wires to another?

A

electromagnetic induction

54
Q

What do electric fields give rise to?

A

Voltages and currents

55
Q

When does induction take place?

A

Whether or not a conductiing wire or any material medium is present

56
Q

What does Faradays law states?

A

that an electric field is created un any region of space in which a magnetic field is proportional to the rate at which the magnetic field changes

57
Q

How is the direction of the magnetic field created?

A

electric field is at right angles to the changing magnetic field

58
Q

What happens when the electric charge happens to be present where the electric field is created…

A

this charge will experience a force

59
Q

For a charge in a wire…

A

the force could cause it to flow as current, or to push the wire to one side

60
Q

For a charge in an evacuated region, like in the chamber of a particle accelerator…

A

the force can accelerate the charge to high speeds

61
Q

A magnetic field is created in any region of space in which….

A

an electric field is changing with time

62
Q

According to Maxwell, the magnitude of the created magnetic field is proportionnal to…

A

the rate at which the electric field changes

63
Q

The direction of the created magnetic field is at _______ angles to the changing electric field.

A

right

64
Q

If you shake a charged rid back and firth in empty space…

A

you will produce electromagnetic waves in space b/c the shaking charge can be considered an electric current

65
Q

What surrounds a changing electric current?

A

a changing electric magnetic field

66
Q

An electromagnetic wave is composed of…

A

oscillating electric and magnetic fields that regnerate each other. no medium is required

67
Q

The oscillating fields emanate (move outward) from the…

A

vibrating harge

68
Q

At any point on the wave, the electric field is…

A

perpendicular to the magnetic field, and both are perpendicular to the direction of motion of the wave

69
Q

What does the speed of the electromagnetic wave depend on?

A

how the motion got started, what forces are acting, and how fast the observer is moving

70
Q

What is the speed of electromagnetic radiation?

A

the speed of light

71
Q

Who discovered the remarkable constancy of the speed of propagating electric and magnetic fields?

A

Maxwell

Preparation for Physics Final (11 decks)

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