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Physics > Magnetism and Electromagnetism > Flashcards

Magnetism and Electromagnetism Flashcards

1
Q

what are the ends of magnets called

A

poles

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2
Q

what is the law of magnetism

A

like poles repel, opposite poles attract

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3
Q

what is an example of non-contact force

A

The attraction or repulsion between two magnetic poles

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4
Q

what are the properties of magnetically hard materials

A
  • difficult to magnetise and do not easily lose their magnetism
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5
Q

what are the properties of magnetically soft materials

A
  • easy to magnetise
  • easily lose their magnetism
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6
Q

what are electromagnets made out of and why

A

magnetically soft materials so they can be made magnetic or non-magnetic as and when required

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7
Q

what are permanent magnets made out of

A

magnetically hard materials

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8
Q

what is a magnetic field line

A

the region around the magnet where a force acts on another magnet or on a magnetic material

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9
Q

what do magnetic field lines show on a diagram

A

the direction and strength of the field

The direction of the magnetic field is shown using arrows
The strength of the magnetic field is shown by the spacing of the magnetic field lines
If the magnetic field lines are close together then the magnetic field will be strong
If the magnetic field lines are far apart then the magnetic field will be weak

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10
Q

what are the two rules of drawing magnetic field lines

A
  • they never touch or cross each other
  • they always go from north to south
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11
Q

where in a magnet is the magnetic field the strongest

A

at the poles

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12
Q

what do the filed lines for attracting magnets and those for repelling magnets look like

A
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13
Q

what do the field lines for two magnets look like (one where the poles line up and one for when they are opposite) long ends facing each other

A

.

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14
Q

what is a uniform field and how is it created

A

one that has the same strength and direction at all points

created when two opposite poles are held close together, it is produced in the gap between them. outside the gap, the field will not be uniform

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15
Q

which side of the magnet are magnetic materials attracted to

A

both

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16
Q

what are some examples of magnetic materials

A

iron
steel
cobalt
nickel

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17
Q

what are some non-magnetic metals

A

zinc
copper
aluminium
magnesium

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18
Q

how would you test to see if a material is a magent

A

bring the material close to the magnet and see if it can be repelled

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19
Q

what are some of the characteristics of a permanent magnet

A
  • made out of hard magnetic materials such as steel
  • a permanent magnet will produce its own magnetic field and will not lose its magnetism
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20
Q

how do you create an induced magnet

A

by putting a magnetic material in a magnetic field

21
Q

how do induced magnets behave

A

they will always attract to permanent magnets

22
Q

practical: investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets

A
  • place magnet on top of piece of paper
  • draw a dot at one end of the magnet
  • place a plotting compass so that the needle points away from the dot drawn
  • draw a new dot at the other end of the needle
  • repeat this process and then link the dots using a smooth cure = this is your field line
  • repeat process from a new starting point

for 2 bar magnets - place them 5cm apart

pencil must be sharp for a clear dot
compass must be read from above not at an angle
compass must be allowed to settle before reading

23
Q

what happens when a current flows through a conducting wire

A

a magnetic field is produced around it

24
Q

what does a circular field pattern tell you about the material producing the magnetic field

A

it has no poles

25
Q

where is the magnetic field strongest and why

A

strongest closer to the wire because magnetic field lines get further apart with distance form the wire

26
Q

how to work out the direction of the magnetic field using the current

A
27
Q

how will increasing the current affect the diagram

A

the field lines will get closer together because the field strength will increase

28
Q

what are the two factors that affect field strength of a wire

A
  • size of the current
  • distance from the conductor (wire)
29
Q

when does the motor effect occur

A

when a wire with current flowing through it is placed in a magnetic field and experiences a force

30
Q

why does the wire experience a force during the motor effect

A

due to two interacting magnetic fields

  • one is produced around the wire due to the current flowing through it
  • the second is the magnetic field into which the wire is placed
31
Q

what does a simple d.c. motor consist of

A
  • a coil of wire that is free to rotate, positioned in a uniform magnetic field
32
Q

why can the d.c. motor continue to rotate

A
  • the current flows through the wire so it will feel an upwards force on one side of the coil and a downwards force on the other side UNTIL it becomes vertical
  • then a split ring commutator swaps the contacts of the coil which reverses the way the current is flowing
  • reversing the direction of the current will reverse the direction of the forces, hence the coil will continue its rotation
33
Q

what are the factors affecting the d.c. motor

A
  • SPEED OF ROTATION can be increased by increasing the current or increasing the magnetic field
  • DIRECTION OF ROTATION can be changed by reversing the direction of the current or reversing the poles of the magnet
  • FORCE SUPPLIED BY MOTOR can be increased by increasing the current, increasing the strength of field or adding more turns in the coil
34
Q

how does a loudspeaker work

A

it consists of a coil of wire which is wrapped around one pole of a permanent magnet

  • an alternating current is passed through the coils of the loudspeaker which creates a constantly changing magnetic field around the coil
  • the magnetic field produced from the coil will interact with the field from the permanent magnet, exerting a force on the coil which will also constantly change direction
  • this force makes the coil oscillate, causing the speaker cone to oscillate, creating the sound waves
35
Q

how can you place the wire to gain maximum interactions between the two field strengths

A

90* to the direction of the magnetic field lines

If the two magnetic fields are parallel there will be no interaction between the two magnetic fields and therefore no force produced

36
Q

how can you change the magnets to increase the magnetic force acting on an object

A

increase the strength of the magnetic field

37
Q

what does each finger represent in Fleming’s left hand rule

A
38
Q

how can an electromagnet be made

A

by winding a coil of wire around a soft magnet (such as iron) and flowing a current through it

39
Q

what is the shape of the magnetic field around electromagnets

A

the same shape as around a bar magnet

40
Q

what are the field lines around a wire

A
41
Q

what does the magnet field look like around a flat circular coil

A
42
Q

how could you increase the strength of this wire

A

coil it to form a solenoid

43
Q

what does the magnetic field of a solenoid look like

A

strong and UNIFORM

44
Q

why does the magnetic field of a solenoid look like this

A

because the fields around the individual coils:
- add together to form a very strong almost uniform field along the centre of the solenoid
- cancel to give a weaker field outside the solenoid

45
Q

in what way are solenoids like bar magnets

A

one end of the solenoid acts like a north pole, the other like a south pole

46
Q

how can you find which side of the solenoid is which pole?

A
  • view it from one end and look inside
  • if the current is travelling in a clockwise direction, then it is the south pole
  • anticlockwise is north pole
47
Q

how can you increase the strength of a solenoid

A
  • increase current
  • increase coils
  • add an iron core through centre of coils
48
Q

what happens to the iron core when a current is flowed through the coils of a solenoid

A

the iron core will become an induced magnet

Physics (13 decks)

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