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Preparation for Physics Final > chapter 36 > Flashcards

chapter 36 Flashcards

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1
Q

Do magnets exert forces on each other?

A

Yes

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2
Q

How are magnets similar to electric charges?

A

They attract and repel without touching, depending on which end is held near the other. The strength of their interaction depends on the distance of separation of the two magnets.

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3
Q

What produces magnetic poles?

A

Electric charges

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4
Q

What do magnetic poles produce?

A

Magnetic forces

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5
Q

Whatt happens when you suspend a bar magnet from its center by a piece of string?

A

It will act as a compass. The end that points northward is called the north seeking pole. The end that points south is called the south seeking pole.

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6
Q

Do all magnets have a north and south pole?

A

Yes

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7
Q

What happens when if the north pole of one magnet is brought near the north pole of another magnet?

A

They repel

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8
Q

Like poles______; opposite poles ________

A

repel; attract

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9
Q

What is the major difference between electric charges and magnetic poles?

A

Electric charges can be isolated and magnetic poles cannot

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10
Q

Are negatively charged electrons and positively charged protons entities by themselves?

A

Yes

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11
Q

Does a cluster of electrons need to be accompanied by a cluster of protons and vice versa?

A

No

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12
Q

Does a north pole exist without the prescence of a south pole?

A

No

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13
Q

Are the atoms themselves magnets?

A

Yes

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14
Q

The ________of the _______field outside a magnet is from the _______ pole to the _______pole.

A

direction; magnetic; north; south

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15
Q

Where the lines are closer together the field strength is ________.

A

greater

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16
Q

Where is the magnetic field strength greatest at?

A

at the poles

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17
Q

What happens if we place another magnet or a small compass anywhere in the field?

A

its poles will tend to line up with the magnetic field

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18
Q

What is magnetism related to?

A

electricity

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19
Q

What is a moving electric charge surrounded by?

A

An electric field and magnetic field.

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20
Q

Why is a moving electric charged also surrounded by a magnetic field?

A

Due to the “distortions” in the electric field caused by motion.

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21
Q

What did Albert Einstein explain?

A

That magnetic field is a relativistic by-product of the electric field

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22
Q

A magnetic field is produced by…

A

the motion of electric charge

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23
Q

Where is the motion of electric charges in a common bar magnet?

A

this moving charge constitutes a tiny current and produces a magnetic field

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24
Q

What does a spinning electron constitute?

A

A charge in motion and thus creates another magnetic field

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25
Q

In most materials, the field due to spinning predominates over…

A

the field due to orbital motion

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26
Q

Is every spinning electrin a tiny magnet?

A

Yes

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27
Q

A pair of electrons spinning in the same direction makes up a…

A

stronger magnet

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28
Q

Do electrons spinning in opposite electrons work with each other? Why or why not?

A

No they work against each other because their magnetic fields cancel.

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29
Q

What are magnetic domains?

A

Clusters of aligned atoms

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30
Q

Describe the domain of the magnetic domains?

A

They are microscopic, and there are many of them in a crytal of iron

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31
Q

What is the difference between a piece of ordinary iron and an iron magnet?

A

The alignment of domains. In a common iron nail, the domains are randomly oriented. When a strong magnet is brought nearby, a growth in size of domains that are oriented in the direction of the magnetic field. This growth is at the expense of domains that are not aligned. A rotation of domains. THe domains become aligned much as electric dipoles are aligned in the prescence of a charged rod. When you remove the nail from the magnet, ordinary thermal motion causes most or all of the domains in the nail to return a random arrangement.

32
Q

How are permanent magnets made?

A
  • by simply placing pieced of iron or certain iron alloys in strong magnetic fields
  • stroke a pice of iron with a magnet,
33
Q

How do alloys of iron differ?

A

Soft iron is easier to magnetize than steel. It helps to tap the iron to nudge any stubborn domains into alignment.

34
Q

What does stroking a piece of iron do?

A

It aligns the domains in the iron.

35
Q

What happens is a permanent magnet is dropped or heated?

A

Some of the domains are jostled out of alignment and the magnet becomes weaker.

36
Q

What does a moving charge produce?

A

a magnetic field

37
Q

What happens when many charges are in motion when a current flows through a conductor?

A

a magnetic field

38
Q

How can the magnetic field that surroucns a current-carrying conductor be demonstrated?

A

by arranging an assortment of amgnetic compassess around a wire and passing a current through it.

39
Q

What is the effect that Oersted first demonstrated?

A

The compasses line up with the magnetic field produced by the current and show it to be a pattern of concentric circles about the wire. When the current reverses direction, the compasses turn completely around, showing that the direction of the magnetic field changes also

40
Q

What happens if the wire is bent into a loop?

A

the magnetic field lines become bunched up inside the loopn

41
Q

What happen if the wire is bent into another loop, overlapping the first?

A

The concentration of the magnetic field lines inside the double loop is twice as much as in the single loop. It follow that the magnetic fiels intensity in this region is increased as the number of loops is increased.

42
Q

What is an electromagnet?

A

a current-carrying coil of wire with many loops

43
Q

What happens if a piece of iron is placed inside the coil of an electromagnet?

A

The magnetic domains in the iron are induced into alignment, increasing the magnetic field intensity.

44
Q

What happens beyond a certain limit of the magnetic field in iron?

A

It “saturates” so iron is not used in the cores of the strongest electromagnets

45
Q

What are electromagnets made of?

A

superconductinf material

46
Q

What can a superconducting electromagnet generate?

A

a powerful magnetic field indefinitely w/out using any power.

47
Q

Will a charged particle at rest interact with a static magnetic field?

A

No

48
Q

If the charged particke moves in a magnetic field…

A

the charged particle experiences a deflecting force

49
Q

When is the force greatest?

A

When the particle moved in a direction perpendicular to the magnetic field lines

50
Q

When does the force become zero?

A

When the particle moves parallel to the field lines

51
Q

The direction of the force is always…

A

perpendicular to both the magnetic field lines and the velocity of the charged particle

52
Q

A moving charge is deflected when…

A

it crosses magnetic field lines but not when it travels parallel to the field lines

53
Q

Since a charged particle moving through a magnetic field experiences a deflecting force…

A

a current of charged particles moving through a magnetic field also experiences a deflecting force.

54
Q

What is the simplest meter to direct electric current?

A

It consists of a magnetic needle on a pivot at the center of a number of loops of insulated wire. When an electric current passes through the coil, each loop produces its own effect on the needle so that a very small current can be detected. A sensitive current-indicating instrument is called a galvanometer

55
Q

THe greater the current in loops…

A

the greater its deflection

56
Q

What may a galvanometer by calibrated to measure?

A

Current (amperes), in which case it is called an ammeter. Or electric potential (volts), in which case it is called a voltmeter

57
Q

If the design of the galvanometer is slightly modified…

A

you have an electric motor

58
Q

What is a permanent magnet used to do?

A

Produce a magnetic field in a region where a rectangular loop of wire is mounted so that it can turn about an axis shown

59
Q

What happens when a current passes through the loop? Why?

A

it flows in opposite directions in the upper and lower sides of the loop. It must do this because if charge flows into one end of the loop, it must flow out the other end

60
Q

What happens if the upper portion of the loop is forced to the left?

A

Then the lower portion is forced to the right, as if it were a galvanometer. But unlike a galvanometer, the current is reversed during each half revolution by means of stationary contacts on the shaft

61
Q

What are brushes?

A

The parts of the wire that brush against the stationary contacts on the shaft.

62
Q

What do the brushes do?

A

They help the current in the loop alternate so that the forces in the upper and lower regions do not change directions as the loop rotates

63
Q

That rotation is continuous as long as…

A

current is supplied

64
Q

How are large DC or AC motor made?

A

by replacung the permanat magnet with an electromagnet that is energized by the power source

65
Q

What is an armature?

A

Many loops wound about an iron cylinder, which then rotates when energized with electric current

66
Q

What did the advent of the motio make it possible to do?

A

Replace enormous human and animal toil by electric power in most parts of the world

67
Q

Why does a compass point northwards?

A

Because Earth itself is a huge magnet. The compass aligns with the magnetic field of the Earth

68
Q

Do the magnetic poles of Earth coincicde with the geographic poles?

A

No, they aren’t even close.

69
Q

What is the discrepancy between the orientation of a compass and true noth known as?

A

Magnetic declination

70
Q

Do we know why Earth is a magnet?

A

No

71
Q

Is the configuration of Earth’s magnetic field different to that of a strong bar magnet placed near the center of Earth?

A

No, it is similar

72
Q

Is Earth a magnetized chunk of iron like a bar magnet?

A

No, it is simply too hot for indivdual atoms to remain aligned

73
Q

What are Earth’s convection current in its molten interior driven by?

A

Rising heat from radioactive decay w/in Earth’s core.

74
Q

Is the magnetic field of Earth stable?

A

No

75
Q

What does the evidence from the rock show?

A

That there have been times when the magnetic field of Earth has diminished to zero and then reversed itself

Preparation for Physics Final (11 decks)

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