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GCSE CCEA Physics unit 2 And 3 > Magnetism And Electromagnetism > Flashcards

Magnetism And Electromagnetism Flashcards

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1
Q

Which 4 materials can be magnetic?

A
  • cobalt
  • iron
  • nickel
  • steel (iron alloy)
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2
Q

What is the pneumonic for the type of electromagnet given by iron and steel?

A

Steel
Permanent
Iron
Temporary

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3
Q

What are the names of the two poles of a bar magnet?

A

North seeking pole
South seeking pole

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4
Q

How do you represent magnetic field on a diagram?

A

By drawing lines of flux / field lines

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5
Q

What direction is flux?

A

Isolated North Pole takes north to south

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6
Q

What 3 factors affect the strength of an electromagnet

How do each affect strength?

A
  • current (more = stronger)
  • number of coils (greater no. Of turns per unit length = stronger)
  • material of core (iron = best)
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7
Q

When conventional current is travelling from:

  • into a page
  • out of a page

, in what direction does the magnetic field travel?

A
  • clockwise (into)
  • anti-clockwise (out of)
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8
Q

When conventional current is travelling from bottom to top, in what direction does the magnetic field travel?

A
  • from a Birds Eye view, anti-clockwise
  • from below, clockwise
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9
Q

When looking down an electromagnet, how can you tell which is the north seeking pole and which is the south seeking pole?

What are the two pneumonics?

A
  • the side where the coil moves up the back of the e.m., conventional current is clockwise
  • the side where the coil comes down the front of the e.m., conventional current is anti-clockwise

ClockwiSe - south
ANti-clockwise - North

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10
Q

What principal is used to determine the direction of magnetic fields?

A

The right hand grip rule

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11
Q

How do lines of flux show the strength of a magnet?

A

The closer the lines, the stronger the magnetic field

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12
Q

Where is magnetic field strongest?

A

The poles

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13
Q

How do opposite magnetic poles attract?

A

The magnetic fields combine to produce a uniform magnetic field

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14
Q

what is a uniform magnetic field?

How is it represented?

A
  • A magnetic field with the same strength at every point
  • represented with parallel lines of flux
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15
Q

How do like magnets repel?

A

The magnetic fields cancel out

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16
Q

How can you detect magnetic fields?

A

Using a compass

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17
Q

What is used to show the shape of a magnetic field?

A

Iron fillings

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18
Q

What is a plotting compass?

A

A small magnetic compass used to show the shape and direction of a magnetic field

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19
Q

Where does the Earth’s magnetic field come from?

A

the Earth’s core, which is made from iron and nickel

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20
Q

How does a compass work? (2)

A
  • The needle of the compass is a small bar magnet
  • that points in the direction of the Earth’s magnetic field
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21
Q

What is produced around a current carrying wire?

A

A magnetic field

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22
Q

How is magnetic field around a current-carrying wire displayed?

A

With circles coming out of the wire

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23
Q

How do you find the direction of magnetic field around a current carrying wire?

A

The right hand grip rule

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24
Q

What is represented in the right-hand grip rule? (2)

A
  • thumb shows the direction of conventional current
  • fingers show direction of the field
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25
Q

What is the effect of length of conductor on the strength of a wire’s magnetic field?

A

Greater length of wire = stronger magnetic field

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26
Q

What is the effect of distance on the strength of a bar magnet’s magnetic field?

A

Greater distance from magnet = weaker magnetic field

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27
Q

What is a solenoid?

What is it used for?

A
  • A wire coiled into a spiral shape
  • used to make electromagnets
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28
Q

Describe how to represent the magnetic field around a solenoid

(2)

A
  • Lines of flux from north seeking pole to south seeking pole
  • lines of flux from south to north through the solenoid
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29
Q

What are the properties of the magnetic field inside a solenoid?

A

Strong and uniform

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30
Q

What is an electromagnet made of?

A

A solenoid with an iron core

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31
Q

What are the advantages of electromagnets over permanent magnets?

A
  • they can be switched off
  • their strength can be changed
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32
Q

What is a magnetic material?

A

Any material that is strongly attracted to a magnet

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33
Q

Give 2 examples of permanent magnets

A
  • bar magnet
  • horseshoe magnet
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34
Q

Where is magnetic force strongest on a magnet?

A

Near the magnet’s poles

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35
Q

What are attraction and repulsion examples of?

A

Non-contact forces between magnetic poles

36
Q

What does a permanent magnet do?

A

Produces its own magnetic field

37
Q

What is an induced magnet?

A

A material that becomes a magnet when placed in a magnetic field

38
Q

What does induced magnetism always do?

A

Always causes a force of attraction

39
Q

What happens when an induced magnet is removed from a magnetic field?

A

It loses most or all of its magnetism quickly

40
Q

How do you test for a magnetic material?

A

See if it is attracted to both ends of a known magnet

41
Q

How do you test for a magnet?

A

See if it can be repelled by one end of a known magnet

42
Q

Explain the motor effect (2)

A
  • When a conductor (wire) carrying current is placed in a magnetic field of a magnet
  • causing the conductor and magnet to exert force on each other
43
Q

What is Fleming’s Left Hand Rule used to find?

How?

A
  • The direction of the force on a conductor in a magnetic field
  • by holding your thumb, forefinger and second finger at right angles to each other
44
Q

Using the Left hand rule, what does your index finger represent?

A

The direction of the magnetic field from north to south

45
Q

Using the Left hand rule, what does your middle finger represent?

A

The direction of the current from positive to negative

46
Q

Using the Left hand rule, what does your thumb represent?

A

The direction of the force on the conductor (wire) carrying the current

(up or down)

47
Q

What factors affect the size of the force on a conductor in a magnetic field?

(3)

A
  • magnetic flux density
  • current through the conductor (wire)
  • length of the conductor (wire)
48
Q

What is Magnetic flux density?

A

A measure of the strength of a magnetic field

49
Q

State the equation linking current, length, force and magnetic flux density

State units

A

F=BIL
Force = (Mag Flux dens) x (current) x (length)

N = T x A x m
Newtons = Tesla x amperes x metres

50
Q

Why does a coil in a magnetic field rotate? (2)

A
  • current in one side of the coil causes a downward force
  • current in the other side of the coil causes an upward force
51
Q

What is an electric motor?

A

A device that uses the motor effect to produce a turning effect in a coil of wire

52
Q

What is a DC motor?

A

An electrical motor that uses direct current to produce a turning effect

53
Q

What is direct current?

A

An electric current that flows in one direction only

54
Q

What is a transformer?

A

A device that can increase or decrease the voltage of alternating current

55
Q

What does a step-up transformer do?

A

Increases voltage by having more turns on the secondary coil

56
Q

What does a step-down transformer do?

A

Decreases voltage by having fewer turns on the secondary coil

57
Q

Describe the structure of a basic transformer

A

A primary coil and a secondary coil wound on an iron core

58
Q

why is laminated soft iron used for the core of a transformer? (2)

A
  • Iron is easily magnetized and demagnetized
  • therefore it provides a path for magnetic flux
59
Q

Why are transformers supplied with alternating current?

A
  • So that the magnetic field produced in the primary coil is continually changing
  • so the secondary coil cuts these field lines, even when not moving
60
Q

State the equation linking the ratio of voltages to the ratio of the number of turns in each coil

State what each symbol means

(Transformers)

A

V1 / V2 = N1 / N2

  • V1 = primary coil voltage,
  • V2 = secondary coil voltage,
  • N1 = no of coils on primary coil,
  • N2 = no of coils on secondary coil
61
Q

What is the other name for voltage?

A

Potential difference

62
Q

How does induced potential difference occur? (3)

A
  • When a conductor cuts magnetic field lines
  • or if there is a change in a magnetic field around a conductor,
  • a potential difference is induced across the ends of the conductor
63
Q

How does induced current occur? (2)

A
  • If the conductor that has had a potential difference induced across its ends in part of a complete circuit,
  • a current is induced in the conductor
64
Q

Explain the generator effect (3)

A
  • When the a conductor cuts magnetic field lines
  • causes a potential difference and a current (if part of a complete circuit)
  • to be induced in a conductor
65
Q

What are the properties of a magnetic field generated by induced current? (2)

A
  • it opposes the original change
  • this can be movement of the conductor or the change in magnetic field
66
Q

How do you reverse the direction of induced potential difference or current?

A

Reverse the direction of movement of the magnet or coil

67
Q

What factors affect the size of induced potential difference/current? (3)

A
  • speed of movement of the coil
  • magnetic field strength being increased
  • number of turns on the coil
68
Q

What is a generator?

A

A device that uses the generator effect to convert kinetic energy to electrical energy

69
Q

What is an alternator? (2)

A
  • An electrical generator which produces alternating current (A.C. Generator)
  • by rotating a coil of wire between the poles of a magnet
70
Q

Under what principal does the a simple generator work?

How?

A
  • The principal of conservation of energy
  • the force required for the bar magnet to overcome the like electromagnetic pole’s magnetic field converts kinetic energy to electrical energy
71
Q

Describe the structure of an alternator

A

A coil of wire rotating in a magnetic field and two slip rings

72
Q

What graph does voltage produced by an a.c. Generator follow?

A

A sine curve

73
Q

What is a dynamo? (2)

A
  • An electrical generator which produces direct current (a d.c. generator)
  • from the kinetic energy of a moving magnet
74
Q

Describe the structure of a dynamo

A

A coil of wire rotating in a magnetic field and a split ring commutator

75
Q

What is the name the sensitive ammeter in a simple generator?

What is it attracted to / where does it point?

What does it measure?

A
  • a centre zero ammeter/galvanometer
  • toward conventional current
  • milliamps or micro-amps
76
Q

Which rules do:

  • a.c.
  • d.c.

Follow?

A
  • a.c. - right hand grip rule
  • d.c. - left hand rule
77
Q

What is electromagnetic induction (EMI)? (3)

A
  • when the magnetic field near a conductor is changed
  • causing the conductor to cut the field lines and electrical voltage to be produced
  • this can be done by changing the current in a neighboring coil (thus changing the magnetic field)
78
Q

In the motor effect, how is force increased? (3)

A
  • increased current
  • stronger magnet used
  • length of wire exposed to magnetic field is increased
79
Q

In the Left Hand Rule, what happens when current and magnetic field are parallel?

A

No force is produced

80
Q

What is the frequency of the mains?

What does this mean?

A
  • 50 Hz
  • it changes direction 100 times per second - 50 complete cycles a second (A.C.)
81
Q

What is the difference between a.c. and d.c.? (In terms of direction)

A

a.c. Is bidirectional and d.c. is unidirectional

82
Q

Why does electromagnetic induction not work when using direct current? (2)

A
  • to induce current there must be a changing magnetic field
  • this is only produced using alternating current, which produces a changing magnetic field
83
Q

What is the voltage in UK households?

A

240V

84
Q

What type of current is supplied to/produced by a transformer

A

A.c.

85
Q

What effect do transformers utilise?

A

Electromagnetic Induction (EMI)

GCSE CCEA Physics unit 2 And 3 (8 decks)

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