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Physics > P4- Magnets > Flashcards

P4- Magnets Flashcards

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1
Q

Define a magnet

A

A material or object which produces a magnetic field

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2
Q

What must all magnets have

A

A north and a south pole and are surrounded by a magnetic field

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3
Q

How do you represent magnetic feilds

A

By using field lines

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4
Q

Which directions must field lines point

A

From the north pole to the south pole

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5
Q

How can you show where a magnetic field is strongest

A

By the denisty of the lines

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6
Q

How do you show a strong magnetic field in a diagram

A

Using densly packed field lines

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7
Q

What can you use to determin the north and south pole of a magnet

A

Using a compass

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8
Q

What are the difference between permanent
and induced magnets

A

Periminate magnets have there own magnetic fields but induced magnets become a magnet when they are placed in a magnetic feild

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9
Q

What are the 3 naturally magnetic elements

A

-iron (Fe)
-cobalt (Co)
-nickel (Ni)

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10
Q

What is the motor effect

A

A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles

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11
Q

What hand do you use to work out the direction of current

A

Left hand

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12
Q

When using flemings left hand rule what does your thumb represent

A

The direction of the force

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13
Q

When using flemings left hand rule what does your fore finger represent

A

The direction of the magnetic field

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14
Q

When using flemings left hand rule what does your middle finger represent

A

The direction of the current

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15
Q

How do you arrange you fingers in flemings left hand rule

A

All at 90 degrees to one another

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16
Q

What does a split ring commutator do

A

Switches the postive and negitve connections every half turn

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17
Q

Why is a split ring commutator used

A

It makes it so that the forces are always acting in the same direction which makes the coil turn the full 360 degrees

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18
Q

How can you increase the speed of the rotation in an electric motor

A
  • Increase the currents
  • Add more coil
  • Use stronger magnets
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19
Q

What can the generator effect also be refered to as

A

Electromagnetic induction

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20
Q

What happens when you move a wire coil through a magnetic feild

A

It induces a potenial difference in a wire

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21
Q

What happens to a coil when you stop moving it through a magneitc field

A

The potential differnce dissapears

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22
Q

What causes the potenial difference in a wire in a magnetic feild

A

The change in the magnetic field is what induces a potential difference

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23
Q

What happens when you change the direction of the wires movements in a magnetic feild

A

The direction of the potential difference changes each time in changes direction

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24
Q

What happens when you move the coil wire along the mangetic field ( back and forth)

A

No potential difference or current will be induced because there is no change in magnetic field

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25
Q

What happens when you close coil when it is moving through a magnetic field

A

A poteinial difference and a current is induced

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26
Q

How do you increase the size of the potential difference in a coil moving through a magnetic field

A
  • Stronger magnets
  • Move the magnets faster
  • Shape the wire into a proper coil
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27
Q

How does using stronger magnets increase the potenial difference

A

Stronger magnets=
Stronger magnetic field= Bigger potential difference

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28
Q

How does moving the magnetic faster increase the potenial difference

A

Faster movements =
Faster magnetic field will change =
Bigger potential difference

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29
Q

How does shaping the wire into a coil increase the potenial difference

A

More turns in the wire =
Bigger poteinal difference

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30
Q

Define a solenoid

A

A solenoid consists of a wire coiled up into a spiral shape. When an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet

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31
Q

What is the magnetic field strength of a solenoid

A

Strong and uniform.

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32
Q

What are generators

A

Devices generate electricity from rotational motion

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33
Q

What are ‘Alternators’ and ‘dynamos’

A

Different types of generators

34
Q

How do Dynamos create electricty

A

They use a split ring comunitator in an electric motor

35
Q

How do Alternators create electrcity

A

They use slip rings and brushed in an electric motor

36
Q

What type of current do Dynamos produce

A

Direct current
(d.c)

37
Q

What type of current do Alternators produce

A

Alternating current
(a.c)

38
Q

How do slip rings and brushes work

A

Slip rings maintain constant contact with the same sides of the coil.

39
Q

What happens to the current in an Alternator as the coil rotates faster
(terms of a graph)

A

The peaks and occalations of the current on a graph get larger

40
Q

Define an induced magnet

A

Any object that can be influenced by magnetic fields, and has the potenial to become a magnet

41
Q

What are the commen magetic materials

A
  • Nickle
    -Cobalt
    -Iron
    -Alloys of the 3 (steel….)
42
Q

Are induced magets perminant

A

No they are only magnets temporarly when in a magnetic field

43
Q

How do create an induced magnet

A

Place a piece of magnetic material(which wasnt actually a magnet) into the feild of a magnet. This induces its own magnetic field.

44
Q

Which type of force will there always be between induced and perminate magnet

A

The force will allways be attractive- North to south

45
Q

What materials are magnetically soft

A
  • Nickle
  • Iron
46
Q

Define Magnetically Soft

A

A material that loses its magnetism quickly when taken out of a magnetic field

47
Q

Define Magnetically Hard

A

A material that loses its magetism slowly after being removed from a magnetic field

48
Q

What materials are Magnetically hard

A
  • Steel
49
Q

What happens when you pass a current through a wire

A

A magnetic field is induced

50
Q

What does the right hand rule show you

A

The direction of a mangetic field in a wire

51
Q

How do you use the right hand rule

A

Curl your hand into a fist and point your thumb in the direction of the current . The direction your fingers are curled in is the direciton of the current.

52
Q

What shape is the magentic field lines on a wire

A

Concentric circles

53
Q

What shape are the magentic field lines in a circlular coil

A

Elipses and a line straight through the middle

54
Q

What is the magnetic field of a soleniod simialar to

A

It is similar to the magnetic field of a bar magent

55
Q

Which way do the arrows point in a magnetic field diagram of a solenoid

A

From North to South

56
Q

What is a solenoid also known as

A

An ElectroMagnet

57
Q

What happens when you stop the current through an Electrogmagnet

A

The magentic field stops

58
Q

How do you reverse the direction of the magentic field in an Electromagnet

A

Reverse the direction of the current

59
Q

How do you increase the strength of an electromagnet

A
  • Increase the current in the solenoid
  • Increase the no. of turns (keep lenght the same)
  • Decrease the lenght of the coil (keep turns no. the same)
  • Add a soft iron core
60
Q

How does the denisty of the turns in a solenoid effect the mangnets strength

A

Densly packed coils have a strong magentic field and less densly packed coils have a weaker magnetic field strength

61
Q

How does adding a soft iron core effect the solenoids strength as a magnet

A

As iron is a soft magnetic material it will become an induced magnet when the solenoid is switched on which increases the magnetic field. It will also lose its magnetic field when the current is switched off

62
Q

Define the motor effect

A

A current carrying wire in the presence of a magnetic field will experience a force

63
Q

What is the eqaution for force experienced by a wire (during the motor effect

A

Force = current x magnetic field strenght x length of wire

64
Q

What is another phrase for magnetic field strength

A

Magnetic flux density

65
Q

What is the magnetic field strength mesured in

A

Teslas (T)

66
Q

What is an oscilloscope

A

A volt meter that shows how voltage varries over time

67
Q

What does the oscilloscope graph of an alternator look like

A

As the current switches direction the oscillations are on both the positve and negitive sides of the graph

68
Q

What happens to an oscilloscope graph of an generator when the coil rotates faster

A

The oscillations get larger and more frequent

69
Q

What does the oscilloscope graph of an dynamo look like

A

As the current is always flowing in the same direction the oscillations always stay on either the positvie or negitve sides of the graph

70
Q

What the role of a transformer

A

To increase of decrease the voltage

71
Q

What are transformers used for in the real world

A

To increase the volatage of electricty made in power stations so they can be transported around the country and to decreace the voltage when it reaches homes

72
Q

What is a step up transformer

A

A transformer that increases the voltage decreases the current

73
Q

What is a step down transformer

A

A transformer that decreases the voltage increases the current

74
Q

What are the parts of a transformer

A

A primary coil
A secondry coil
An iron core

75
Q

What is the coil ratio in a step up transformer

A

The primary coil has less turns that the secondry coil

76
Q

What is the coil ratio in a step down transformer

A

The primary coil has more turns than the secondry coil

77
Q

What type of current must be used in a transformer

A

An alternating current

78
Q

How do transformers work

A
  1. When supplied with an alternating current, the primary coil will generate a magnetic field
  2. This then induces an alternating magnetic field in the iron core
  3. This induces an alternating voltage in the secondry coil which (if the circit is complete) leads to an alternating current in the secondry coil
79
Q

The ratio of turns in the primary and secondry coil affects…

A

The current and voltage in the secondry coil

80
Q

What are the wires in transformers covered in

A

They are insulated in plastic

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