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physics paper 2 > P7 | magnetism & electromagnetism > Flashcards

P7 | magnetism & electromagnetism Flashcards

1
Q

what are the two poles on a magnet?

A

north and south

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2
Q

where is the magnetic force felt the most strongest in a magnet?

A

at the ends - poles

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3
Q

what type of forces are magnetic forces?

A

non-contact forces

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4
Q

give 3 magnetic elements

A

iron, cobalt and nickel

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5
Q

what are some features of permanent magnets?

A
  • produce their own magnetic field
  • can’t be turned on or off
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6
Q

what are some features of induced magnets?

A
  • doesn’t produce its own magnetic field
  • becomes a magnet when placed in another magnet’s magnetic field
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7
Q

what can you use to plot magnetic field lines?

A

iron filings or a compass - must always put arrows to show direction of magnetic field
the current travels from the north pole to the south pole

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8
Q

what direction does the magnetic field go around a magnet?

A

from the north pole to the south pole

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9
Q

define flux density

A

the density of field lines which indicate the strength of the magnetic field

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10
Q

what happens when two magnets are brought close to each other?

A

they exert a force on each other

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11
Q

what type of force is exerted if two like poles of a magnet are brought near each other?

A

a repulsive, non-contact force

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12
Q

what type of force is exerted if two unlike poles of a magnet are brought near each other?

A

an attractive, non-contact force

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13
Q

what type of force does induced magnetism always cause?

A

a force of attraction

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14
Q

what is a magnetic field?

A

the region surrounding a magnet where another magnet or magnetic material experiences a non-contact force

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15
Q

what is the force like between a magnet and magnetic material?

A

it is always attractive

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16
Q

how does the strength of a magnetic field alter as you move further away from the magnet producing it?

A

the magnetic field strength decreases the further you move away from the magnet

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17
Q

what does a magnetic compass contain?

A

a small bar magnet that points in the direction of the earth’s magnetic field

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18
Q

what is produced when current flows through a conducting wire?

A

a magnetic field is produced around the wire

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19
Q

what determines the strength of the magnetic field around a current-carrying wire?

A
  • the magnitude of the current flowing through the wire
  • the distance from the wire
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20
Q

what is a solenoid?

A

a coil of wire which when current passes through creates a strong magnetic field

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21
Q

describe the magnetic field found inside a solenoid

A

strong and uniform

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22
Q

what is an electromagnet?

A
  • a solenoid with an added iron core
  • adding the iron core increases the strength of the magnetic field
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23
Q

what is the motor effect?

A

when a force is exerted between a magnetic field and a current-carrying conductor placed in that field

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24
Q

what rule is used to determine the force experienced due to the motor effect?

A

fleming’s left hand rule

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25
Q

what does the thumb represent in fleming’s left hand rule?

A

movement

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26
Q

what does the first finger represent in fleming’s left hand rule?

A

the direction of the magnetic field (points from N to S)

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27
Q

what does the second finger represent in fleming’s left hand rule?

A

the direction of the current flow in the conductor (points from + to -)

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28
Q

what factors affect the strength of the electromagnet?

A
  • current in the coil - the greater the current, the greater the strength
  • no of turns in the coil - the more turns, the greater the strength
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29
Q

what factors affect the size of the force on a current-carrying wire in a magnetic field?

A
  • the magnitude of the current flowing through the conductor
  • the strength of the magnetic field that the conductor is placed in
30
Q

if the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

A

the direction of the force is reversed

31
Q

if the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

A

the strength of the force is increased

32
Q

what criteria must be met for the equation linking force, magnetic flux density, current and length to hold?

A

the conductor must be at right-angles to the magnetic field it is placed in

33
Q

what is the unit used for magnetic flux density?

A

tesla, T

34
Q

in a calculation question, what do you do when asked to work out the angle?

A
  • measure angle with protractor
  • after using the equation (F = BIL) add sin (angle measured by protractor) to find out the angle
35
Q

what are three ways to increase the force in a motor effect?

A
  1. increase the current
  2. increase the magnetic field strength
  3. increase the length of the conductor
36
Q

how do electric motors work?

A
  • direct current is passed through wire
  • each side of the coil experiences opposite forces
  • coil rotates
37
Q

what does a split ring commutator do?

A

changes the current direction every half turn - forced in the same direction every half turn as the sides swap

38
Q

what does it mean when the field lines are closer together?

A

the field is stronger

39
Q

what factors does the magnetic field strength depend on?

A
  1. size of the current
  2. distance from the wire
40
Q

what effect does the twisting a wire into a solenoid have?

A

it increases the magnetic field strength around the wire

41
Q

the magnetic field inside a solenoid is…

A

strong and uniform

42
Q

how can you further increase the strength of the magnetic field in a solenoid?

A

by adding an iron core

43
Q

how is a solenoid different from an electromagnet?

A

an electromagnet is a solenoid with an iron core - it is a magnet that can be switched on and off

44
Q

what is the magnetic field like outside if a solenoid?

A
  • just like a bar magnet - ends of a solenoid act like the north pole and south pole of a bar magnet
  • you can work out which side is which using the right-hand screw rule
45
Q

how can the north pole of the solenoid be found?

A

wrap hands around the solenoid with fingers pointing in the direction of the current - the thumb points in the direction of the north pole

46
Q

what are factors impacting strength of magnetic field?

A

the current and distance from the wire

47
Q

how can the motor effect be increased?

A
  • increasing the current
  • increasing the length of the conductor
  • increasing the flux density
48
Q

what will happen if the direction of the current or magnetic field is reversed?

A

the direction of the force will reverse

49
Q

what is a motor?

A

a current carrying conductor which rotates in a magnetic field

50
Q

why do motors rotate in magnetic fields?

A

the current going up one side of the coil is in the opposite direction to the current going down the other side of the coil

51
Q

why will a wire move when you put it in a magnetic field?

A
  • the wire has a current flowing through it, causing it to have a magnetic field
  • the magnetic field around the wire interacts with the magnetic field around the permanent magnet
  • because of the interaction of those two magnetic fields there is a force acting on that wire, causing it to move
52
Q

explain how fleming’s left hand rule can be used to predict the direction in which the copper rod will move

A
  • hold all the fingers at right angles to each other
  • thumb - direction of the force
  • first finger - field
  • second finger - current
53
Q

what changes to equipment would increase the force on the copper rod?

A
  • decrease the resistance of the variable resistor
  • use stronger magnets - a stronger force will be exerted
54
Q

if it has a solenoid, why would a door unlock when the switch is closed?

A
  • the solenoid is a coil of wire with current travelling through it
  • this creates a magnetic field
  • which attracts the bolt
55
Q

give two ways the resultant force on the bolt could be increased

A
  • adding more turns to the solenoid
  • increasing the current
56
Q

explain why the iron rods move apart when the switch is closed

A
  • the rods become induced magnets
  • they have the same polarity
57
Q

what links the force, current and field in fleming’s left hand rule?

A

they are all directly proportional to each other
e.g if the force reverses, so will the current

58
Q

if the magnetic field is reversed, what happens to the force?

A

it is reversed

59
Q

if the current is increased, what happens to the force?

A

it increases

60
Q

describe the motion of the coil until it comes to an end

A
  • the coil will continue to rotate slowly
  • opposing forces will eventually bring it to rest
61
Q

what three features of an electromagnet control the strength of the magnetic field obtained?

A
  1. the number of turns in the coil
  2. the current flowing through the coil
  3. the material of the core
62
Q

what can make copper rollers move faster?

A
  • increasing the current
  • increase the speed of the motor
63
Q

closing the switch creates a force that acts on the wire XY
explain why a force acts on the wire XY when the switch is closed

A
  • the current flows through it - this means there is a magnetic field produced
  • this means the magnet and the wire will create a magnetic field
  • this is the motor effect
64
Q

what happens when a conductor carrying a current is placed in a magnetic field?

A
  • the magnet producing the field and the conductor exert a force on each other
  • this is called the motor effect
65
Q

if a battery is replaced with a low frequency alternating current (a.c.) power supply, what would the movement of the wire be like? why?

A
  • the magnetic field of the wire will change, causing the wire to move back and forth
  • the direction of the magnetic force acting on it changes continuously
66
Q

what changes would increase the force acting on the wire?

A
  • increasing the current
  • using stronger magnets so a stronger force is exerted
67
Q

what two changes would reverse the direction of the force acting on the wire?

A
  • reversing the direction of the current
  • reversing the magnetic field
68
Q

why would an electromagnet would be used rather than a permanent magnet?

A
  • an electromagnet can be switched on and off
  • a permanent magnet can’t be switched on and off
69
Q

what happens if you place a wire between two poles of magnets?

A
  • the magnets each have their own magnetic field
  • this will cause a reaction and a force being produced on the wire (pushing it out the wire)
70
Q

what happens if the wire is not at 90°?

A

it won’t experience as much of a force

physics paper 2 (1 decks)

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