P4 - magnetism and magnetic fields Flashcards

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1
Q

what is an alternator?

A

also called AC generator

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2
Q

what is current?

A

rate of flow of charge

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3
Q

`what is a diaphragm?

A

the part of a loudspeaker that moves to produce a pressure wave in the air i.e. sound

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4
Q

what is a dynamo?

A

also called DC generator

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5
Q

what is electromagnetic induction?

A

the process of producing an induced potential difference in a conductor due to the conductor cutting magnetic field lines

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6
Q

what is a generator?

A

a device that converts KE into electrical energy; consists of a rotating wire in a magnetic field

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7
Q

what does induced mean?

A

to bring about; make happen

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8
Q

what is magnetic flux density?

A

same as magnetic field strength

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9
Q

what is a motor?

A

a component that produces rotation from the combination of the fields due to magnets and current carrying wires

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10
Q

what is a solenoid?

A

a coil of wire used in an electromagnet

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11
Q

what is a split ring commutator?

A

keeps the coil rotating in the same direction by reversing the direction of current every half turn

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12
Q

what is a transformer?

A

a component that uses two coils and an iron core to change the potential difference in a circuit

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13
Q

what is a Tesla?

A

the unit of magnetic flux density

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14
Q

what is a magnetic field?

A

a region where a magnetic material will experience a force

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15
Q

magnetic field lines always point …

A

from north to south

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16
Q

the strength of the field is shown by …

A

how close the field lines are to eachother

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17
Q

the magnetic field is always strongest …

A

at the poles

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18
Q

what are the only 3 magnetic elements?

A
  • iron
  • nickel
  • cobalt
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19
Q

what are bar magnets?

A
  • permanent magnets
  • contain aligned magnetic domains
  • retain their magnetism and so are called magnetically hard materials
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20
Q

what does an iron nail have?

A

randomly aligned domains

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21
Q

what will happen to an iron nail when placed in a magnetic field?

A
  • the domains will line up, producing an induced magnet
  • by banging the magnet the domains then randomly align again because the nail is made of a ‘soft’ magnetic material
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22
Q

how do we know the Earth has a magnetic field?
where does it come from?

A
  • the Earth’s magnetic field is caused by iron ions moving (convection currents) inside the Earth’s core
  • we know the shape of the Earth’s magnetic field because scientists take compasses around the world and are able to map the magnetic filed lines since the compasses line up with them
  • the North Pole of a magnet is attracted to the geographic North Pole of the Earth because there is a magnetic South Pole there
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23
Q

when an electric current flows in a wire, what shape is the magnetic field it produces?

A

circular

24
Q

what does the direction of the field depend on?

A

the direction of the current

25
Q

as the distance away from the wire increases, what happens to the field strength?

A

it decreases

26
Q

how do we show the magnetic field strength decreasing as distance increases?

A

the field lines getting further apart

27
Q

what does the magnetic field pattern around a solenoid take the same shape as?

A

as that around a bar magnet

28
Q

what can the strength of the magnetic field be increased by?

A
  1. more turns on the coil/loops
  2. more current/increase the current
  3. add an iron core
29
Q

investigation:
how does increasing the current in a solenoid affect the strength of the electromagnet?
- what are the variables in this investigation?

A

dependent variable = number of paperclips picked up
independent variable = current
control variables = size of paperclips, nail, no. of turns in solenoid

30
Q

method for investigation for how does increasing the current in a solenoid affect the strength of the electromagnet?

A
  1. set up circuit
  2. use variable resistor to adjust/vary he current to chosen values e.g. 0, 0.25, 0.5, 0.75 etc
  3. at each current, place the nail into a pile of paperclips and record how many are picked up
  4. repeat the experiment so you have three values of paperclips for each current value
  5. calculate the mean average paperclips and plot data onto a graph
31
Q

what is formed when a current flows through a solenoid?

A

a magnetic field

32
Q

what is the device called that consists of a current flowing through a solenoid and forming a magnetic field?

A

an electromagnet

33
Q

what will happen if an iron core is added into the centre of an electromagnet?

A

the iron will be magnetised by the electromagnet’s field, creating another magnetic field, this time around the iron core; these two fields add together to create one stronger magnetic field

34
Q

what are 2 advantages of using electromagnets instead of permanent magnets?

A
  1. they can be made very strong
  2. they can be turned on and off rapidly
35
Q

what is the motor effect?

A

when a current-carrying conductor (i.e. wire) is placed in a magnetic field, it experiences a force, which causes it to move

36
Q

why does the motor effect occur?

A

the effect occurs because we are combining two magnetic fields and so each object experiences a magnetic force (similar to when you bring two magnets together)

37
Q

how do we predict the direction of the force?

A

Fleming’s left hand rule

38
Q

what is Fleming’s left hand rule?

A

thumb = motion
first finger = magnetic field (points to south)
second finger = current (points to negative)

39
Q

how can we increase the size of the force on the wire?

A
  1. more current
  2. stronger magnet
  3. increase the length of the conductor in the magnetic field
40
Q

how do we change the direction of the force on the wire?

A
  1. swap the position of the north and south pole
  2. change the direction of current (turn the cells around)
41
Q

what does a DC motor contain?

A
  • split ring commutator
  • magnets
  • battery
  • brushes
  • axle
  • coil
42
Q

how does a DC motor work?

A
  • a current flows through the coil which is in a permanent magnetic field; this current causes its own magnetic field to form
  • the right side of the coil experiences a downwards force due to Fleming’s left hand rule
  • on the left side of the coil, the current is flowing in the opposite direction relative to the magnetic field and so it experiences an upwards force
  • this makes the coil rotate
  • the split ring commutator keeps the coil rotating in the same direction by reversing the direction of current every half turn
43
Q

why do motors use magnets with curved poles?

A

motors have curved magnets so that the distance between the coil and the magnet is kept constant and as small as possible (remember magnetic field strength decreases with distance)

44
Q

how can the DC motor be made to rotate faster?

A
  1. stronger magnets/magnetic field
  2. increase the current
  3. add more turns on the coil
45
Q

demo 1: stationary magnet, moving conductor
- what happened when the wire was moved down between the poles of the magnet?

A

current was generated

46
Q

demo 1: stationary magnet, moving conductor
- what happened when the wire was moved up between the poles of the magnet?

A

current flowed the other way

47
Q

demo 1: stationary magnet, moving conductor
- what happened when the wire was moved more slowly?

A

less current

48
Q

demo 1: stationary magnet, moving conductor
- what happened when the wire was held still between the poles of the magnet?

A

no current

49
Q

demo 1: stationary magnet, moving conductor
- what happened when the wire was moved horizontally between the poles?

A

no current

50
Q

demo 1: stationary magnet, moving conductor
- what happened when the magnet was turned around?

A

current flows the other way

51
Q

demo 2: stationary conductor, moving magnet
- what happened when the magnet was pushed into the coil?

A

current was generated

52
Q

demo 2: stationary conductor, moving magnet
- what happened when the magnet was at rest inside the coil?

A

no current

53
Q

demo 2: stationary conductor, moving magnet
- what happened when the magnet was pulled out of the coil?

A

current flows the other way

54
Q

demo 2: stationary conductor, moving magnet
- what happened when the magnet was moved faster?

A

more current

55
Q

demo 2: stationary conductor, moving magnet
- what happened when the magnet was turned around?

A

current flows the other way

56
Q

what is Faraday’s Law?

A

the faster the magnetic field lines are cut the greater the induced potential difference (and therefore current)