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Physics > P15 -Electromagnetism > Flashcards

P15 -Electromagnetism Flashcards

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1
Q

What are the two ends of a magnet called

A

poles

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2
Q

where are the magnetic forces of a magnet the strongest

A

at the poles

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3
Q

what happens when we bring two magnets close together

A

they exert a force on eachother .

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4
Q

what happens when we bring two like poles together

A

they repel

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5
Q

what happens when we bring two unlike poles together

A

they attract

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6
Q

what is the attraction and repulsion of two magenitc poles examples of and why

A

examples of non contact forces because the magnets do not have to touch each other to experience the force .

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7
Q

what is a permanent magnet - give an example

A

a permanent magnet produces its own magnetic field , a bar magnet .

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8
Q

what happens when we bring a permanent magnet next to another permanent magnet

A

then they can attract or repl eachother depending on the direction .

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9
Q

what is an induced magnet

A

an object that becomes a magnet when it is placed in a magnetic field .

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10
Q

when does induced magnetism cause a force of attraction

A

induced magnetism always causes a force of attraction .

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11
Q

describe what happens when a permanent magnet is placed between two induced magnets .

A

There is a magnetic field around the permanet magnet.
The magnetic field has caused the two objects to become magnets .
These are now induced magnets

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12
Q

what happens if we take away the permanet agnet between the induced magents .

A

the induced magents lose most or all of their magnetism quickly

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13
Q

what are the four types of magnetic material

A

iron
steel (alloy of iron)
cobalt
nickel

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14
Q

what are permanent magnets made of and hwy

A

permanent magnests are made of steel as steel dosen’t demagnetise easily .

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15
Q

what is a a magnetic field

A

a magnetic field is a region around a magnet where a force act on another magnet or on a magnetic field .

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16
Q

what happens if we place a magnetic materal into this field

A

it will experience a force of attraction towards th magnet .

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17
Q

what will happen if we place iron into a magnetic field

A

the piece of iron now becomes an induced magnet

this is now attracted to the permanent magnet .

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18
Q

what does the strength of a magnetic field depend on

A

the distance from the magnet

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19
Q

what will happen if we place another piece of iron into the magnetic field but further away

A

the iron still expereices a force of attraction towrds the magnet .
however , the force of attraction is now smaller than the force experienced closer to the magnet .
the field is also strongest at the poles of the magnet .

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20
Q

how can we find the direction of a magnetic field

A

using a compass

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21
Q

why can we use a compass to find a magnetic field

A

as a magnetic compass contains a small bar magnet .

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22
Q

what can we do if we place a compass near a bar magnet

A

we can plot the magnetic field

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23
Q

what is the direction of a magnetic field

A

magnetic field lines always run from the north pole to the south pole .

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24
Q

by looking at the magnetic field lines , how can we tell where the field is the strongest

A

where the lines are more concentrated (close together) shows where the field is the strongest .

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25
Q

how can we tell the earth has its own magnetic field

A

if we hold the compass away from any magnets , then the needle always points in the North-south direction . This tells us that the Earth has its own magnetic field .

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26
Q

what causes the Earth’s magnetic field

A

the Earth’s core

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27
Q

is steel a permanent magnet

A

yes

28
Q

steel is magnetically hard , what does this mean

A

steel is harder to magnetise but will stay magnetic .

29
Q

how can u demagnetise steel

A

by hitting it violently .

30
Q

is iron a permanent magnet

A

no

31
Q

how can you turn iron into a magnet

A

by placing it into a magnetic field .

32
Q

iron is magnetically soft , what does this mean

A

iron is easy to magnetise , but won’t stay magnetic

33
Q

if you were to d othe magnet , iron filing experiment , where would do the iron filings go and why

A

the iron filings are attracted to the poles , shwoing the magnetic field is the strongest around the poles .

34
Q

what is the strength at the neutral point and why

A

the two like poleds together cancel eachother out so overal magnetic field strength is o .

35
Q

what happens when we close the switch of a circuit

A

an electric current flows around the circuit .

36
Q

what happens when a current flows through a conducting wire

A

a magnectic field is produced around the wire

37
Q

how can we prove there is a magnetic field around the wire

A

by using a compass

  • when the current is turned off , the compass needle , lines up with the Earth’s magnetic field .
  • However , when we turn on the current again , the compass needle defects , proving there is a magnetic field around the wire .
38
Q

in a circuit , what does the strength of a wire depend on

A

it depends on the size of the current .

39
Q

what does a larger current mean

A

a stronger magnetic field .

40
Q

what happens as we move further from the wire

A

the strength of the magnetic field decreases .

41
Q

what happens if we change the direction of the current

A

we change the direction of the magnetic field .

42
Q

what happens if we reverse the convetional current

A

the magnetic field also reverses . a copass placed near this wire would deflect in th opposite direction it did before .

43
Q

what is a solenoid

A

coiled wire

44
Q

what is another way to increase the strength of a magnetic field

A

s to coil the wire .

45
Q

what happens when we turn on the current with a solenoid

A

we get a strong and uniform magnetic field inside the solenoid .

46
Q

how are magnetic field lines of a solenoid shaped

A

magnetic field lines of a solenoid have a smilar hsape tor the magnetic field around a bar magnet .

47
Q

RECAP: What are the three ways to increase the strength of a magnetic field produced by a solenoid (explained)

A
  1. if we increase the size of the current we increse the strength of the magnetic field .
  2. the strength of the magnetic field increases if we increase the number of turns of the coil -the solenoid has more turns thn the previous one so the magnetic field is greater .
  3. If we place a piecie of iron insde e the solenoid (an iron core ), this also increases the strength of th emagnetic field .
48
Q

what is an electromagnet

A

a solenoid containing an iron core

49
Q

Give two reasons about how electromagentns are usueful

A
  1. We can change the strength of the magentic field by changing the size of the current .
  2. We can also turns electromagnets on and off .
50
Q

What is the motor effect

A

when a force acts on a wire (or any other conductor) in a magnetic field when a currennt is passed through the wire .

51
Q

(motor effect) the size of the force can be increased by

A
  • increasing the current

- using a stronger magnet

52
Q

what happens to the force when the wire is perpendicular to the magnetic field .

A

the conductor will experience a force.

53
Q

what happens to the force when the wire is parrallel to the magnetic force

A

the conductor will experience 0 force .

54
Q

what factors effect the size of the force (motor effect)

A

magnetic flux density of mg
current in the conductor
length of the conductor

55
Q

what is the magnetic flux density

A

a measure of the strength of the magnetic field .

56
Q

what is the direction of the force .

A

The direction of the force is always at right angles to the wire .

57
Q

what equation can we use to calculate the size of the force ;

A

f=b x i x /

58
Q

in flemigns left hand rule . what does the first finger stand for .

A

the direction of the magnetic field .
second finger, direction of the conventional currrent .
thumb - direction of the motion (the force)

59
Q

explain how a solenoid can be used to pick up and then drop a toy car (6marks)

A

when you connect a solenoid to a battery , a current is passed through the wire .
This produces a magnetic field around the solenoid .
the car is made from a magnetic material such as steel so is attracted to the (poles) of the solenoid .
switching of the electroagnet , reduces th current , the magnetic field disappers and the car is no longer attarcted so falls under gravity .

60
Q

explain why the coil of a simple elecric motor rotates continuously when the motor is connected to a battery .

A

the coil spins becaue a force avcts on each side of the coil due to the motor effect.
the force on one side is in rhw opposite direction to the force on the other side .

61
Q

explain why a simple electric motor connected to a battery reverses if the battery connections are reversed.

A

the direction of the force is revrsed if either the direction of the current or the magnetic field is revrsed .

62
Q

would an electric motor run faster if it was on a plastic block why

A

yes it would run faster because it is lighter .

63
Q

would an electric motor run faster if it was on an iron block

A

yes as the iron block has its own magnetic field .

64
Q

how does a solenoid generate a magnetic field

A

A current-carrying wire generates its own magnetic field. By bending the wire into a
coil, the magnetic field from each turn overlaps with the fields from the neighbouring
turns, creating one big field.

65
Q

how does a motor operate

A

The side of the coil nearest the north pole experiences an upwards force because it’s
carrying a current. The other side of the coil carries a current in the opposite direction
– near the south pole – so experiences a downwards force. These forces cause the
coil to rotate clockwise. The brush contact from the split ring then swaps the current direction so the
process can repeat and the coil keeps rotating clockwise.
(as at 90 degrees stops rotating )

Physics (20 decks)

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