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new science > P4 electricity and magnetism > Flashcards

P4 electricity and magnetism Flashcards

1
Q

Describe the forces between magnetic poles

A
  • ends of magnet called poles
  • 2 poles: north and south
  • like poles repel, opposite poles attract
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2
Q

Describe what is meant by a magnetic field

A

A region in which a magnetic pole experiences a force

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3
Q

Which way do magnetic field lines point

A

Direction of force of N pole

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4
Q

What is produced if a bar magnet is cut in half

A

Two magnets, each with N pole and S pole

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5
Q

What are the magnetic materials

A
  • nickel
  • cobalt
  • iron
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6
Q

Differences between properties of temporary/permanent magnets

A

Temporary:
- soft magnetic material (eg soft iron)
- easy to magnetise/demagnetise

Permanent:
- hard magnetic material (eg steel)
- hard to magnetise/demagnetise

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7
Q

Describe induced magnetism

A
  • when permanent magnet attracts magnetic material, induces magnetic field in material
  • depending on which pole it’s attracted to, induce pole
  • when removed, magnetic field no longer present and lose magnetism
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8
Q

Difference between magnetic and non-magnetic materials

A

Magnetic materials experience a force when placed near a magnet

Non-magnetic materials do not

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9
Q

Difference between permanent magnet and electromagnet

A
  • constant magnetic field // variable strength magnetic field
  • cannot be switched on or off // can be switched on and off quickly
  • north and south poles cannot be swapped // north and south poles can be changed by changing direction of current flow
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10
Q

What types of charges are there

A

Positive and negative

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11
Q

Describe electrostatic charging by friction

A
  • transfer of electrons
  • gain electrons: negative
  • lose electrons: positive
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12
Q

Measurements for charge

A

In coulombs (Q)

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13
Q

Describe what is meant by an electric field

A

Region in echo an electric charge experiences a force

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14
Q

Direction of electric field

A

Direction of force on positive charge

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15
Q

Define electric current

A

The charge passing a point per unit time

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16
Q

Define electric current

A

Charge passing a point per unit time

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17
Q

Equation for charge

A

I = Q/t

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18
Q

Describe electrical conduction in metals

A
  • movement of delocalised electrons
  • carry negative charge
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19
Q

Direction of conventional current

A

Positive to negative

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20
Q

Direction of flow of electrons

A

Negative to positive

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21
Q

Difference between alternating/direct current

A

Moving charges continuously change direction // moving charges flow in one direction only

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22
Q

Define electromotive force

A
  • electrical work done by a source
  • in moving a unit charge around a complete circuit
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23
Q

Units for electromotive force

A

Volts (V)

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24
Q

How is voltage distributed in series circuit

A

Shared between components

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25
Q

Define potential difference

A
  • work done by unit charge
  • passing between 2 points in a circuit
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26
Q

Units for potential difference between 2 points

A

Volts (V)

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27
Q

Equation for resistance

A

R = V / I

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28
Q

Relationship between resistance and wire length

A

Directly proportional

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29
Q

Relationship between resistance and cross sectional area of wire

A

Inversely proportional

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30
Q

Current-voltage graph for resistor with constant resistance

A
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31
Q

Current-voltage graph for resistor with constant resistance

A
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32
Q

Unit for electrical resistance

A

Ohms (Ω)

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33
Q

what do electric circuits do

A
  • transfer energy from source of electrical energy (eg electrical cell, mains supply)
  • to circuit components and then into surroundings
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34
Q

equation for electrical power

A
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35
Q

equation for electrical energy

A
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36
Q

equation for energy in kilowatt hours

A

power (kW) * time (hours)

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37
Q

electrical symbol for cells

A
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38
Q

function of electrical cells

A
  • provide direct current
  • store of energy
39
Q

electrical symbol for batteries

A
40
Q

function of batteries

A
  • series of cells
  • larger store of energy than one cell
41
Q

electrical symbol for ac power supply

A
42
Q

function of ac power supply

A
  • provide ac current
  • store of energy
43
Q

electrical symbol for dc power supply

A
44
Q

function of dc power supply

A
  • provide dc current
  • store of energy
45
Q

electrical symbol for switch

A
46
Q

function of switch

A
  • open/close circuit
  • turn devices on/off
47
Q

electrical symbol for fixed resistor

A
48
Q

function of fixed resistor

A
  • resists flow of electrons
  • limits current
49
Q

electrical symbol for variable resistor

A
50
Q

function of variable resistor

A
  • changes resistance and thereby changes current
  • dimmer switches
51
Q

electrical symbol for heaters

A
52
Q

function of heaters

A
  • transfer electrical energy to thermal energy
  • heats room/space
53
Q

electrical symbol for lamps

A
54
Q

function of lamps in circuit

A
  • transfers energy into light
  • lighting
55
Q

electrical symbol for motors

A
56
Q

function of motor in circuit

A
  • use current to make spinning motion
  • store of kinetic energy
57
Q

electrical symbol for ammeter

A
58
Q

function of ammeter in circuit

A
  • measures current
58
Q

electrical symbol for voltmeter

A
59
Q

function of voltmeter in circuit

A
  • measures potential difference
59
Q

electrical symbol for fuses in circuit

A
60
Q

function of fuses in circuit

A
  • breaks circuit if too much current
  • safety device
61
Q

electrical symbol for generators

A
62
Q

function of generators in circuit

A
  • use kinetic energy to produce current
  • generate electricity
63
Q

electrical symbol for light-emitting diodes (LEDs)

A
64
Q

function of LEDs in circuit

A
  • emits light of specific colour when current flows
  • low energy lighting
65
Q

does current change in series circuit

A

no

66
Q

how to place LED symbol in circuit diagram

A

place arrow facing conventional current

67
Q

does current flow both ways in LED

A

no, only one

68
Q

relationship between combined pd and emf in series circuits

A

sum of pd across resistors equal to battery power (emf)

69
Q

how to calculate combined resistance of resistors in series

A

add them up

70
Q

relationship between sum of currents entering junction in parallel circuit and leaving junction

A

equal

71
Q

relationship between pd across components in series circuits and sum of individual pd across each component

A

equal

72
Q

relationship between pd across each branch of parallel arrangement of components and pd of whole arrangement

A

equal

73
Q

advantages of connecting lamps in parallel in a circuit

A
  • pd across each lamp in parallel equally bright
  • brighter
74
Q

how does current change at junction of parallel circuit

A

branches off

75
Q

how to calculate resistance in parallel circuits

A
76
Q

how is combined resistance of 2 resistors in parallel diff to either resistor by itself

A

resistors in parallel have less resistance than the one on its own

77
Q

describe heating effect of current

A

current increases, heat increases

78
Q

electrical hazards include:

A
  • damaged insulation
  • overheating cables
  • damp conditions
  • excess current from overloading of plugs, extension leads, single and multiple sockets when using mains supply
79
Q

hazards of damaged insulation (electricity)

A
  • if insulation damaged and exposed live wire touched
  • will be electrocuted
80
Q

hazards of overheating cables

A
  • large current flow thru appliance
  • causes it to heat up
  • can potentially cause fire
81
Q

hazards of damp conditions (electrical safety)

A
  • water conducts electricity
  • can be electrocuted by simply touching electrical appliance when wet, or when hands wet
82
Q

hazards of excess current from overloading of plugs, extension leads, single and multiple sockets when using mains supply

A
  • draw too much current thru one socket
  • overloads socket
  • may result in fire
83
Q

what are the main safety devices in electrical appliances

A
  • earthing/non-conducting metal cases
  • fuses
  • trip switches
84
Q

use and operation of trip switches

A
  • if current flowing between live and neutral wires increases rapidly
  • trip switch detects, open switch to break circuit
  • rating must be slightly above amt of current applianced designed to use
85
Q

use and operation of fuses

A
  • has thin wire inside, connected to live wire
  • if too much current flows thru live wire, wire melts (fuse blows) and breaks circuit
  • turns off electrical device
86
Q

fuse ratings and use?

A
  • rating must be lowest value
  • which is greater than amount of current appliance designed to use
87
Q

how do earthing metal cases work

A
  • earth wire connected to outer metal casing of appliance
  • prevent lethal shock if fault makes case live
  • provide path for current to flow to earth
  • current likely to flow to ground instead of thru person (lower resistance)
88
Q

what items required to make an electromagnet

A
  • coil of wire
  • power supply
89
Q

how can an emf be induced across a conductor

A
  • conductor moving across a magnetic field
  • changing magnetic field linking with a conductor
90
Q

factors affecting magnitude of an induced emf

A
  • force/speed at which magnet/wire moved
  • strength of magnet
91
Q

describe a simple form of a.c. generator

A
  • rectangular coil of wire continuously rotates within magnetic field
  • generate induced emf
  • slip rings are cylindrical conductors that make constant contact w coil during rotation, allow direction of induced emf to alternate
92
Q

p4.5.2??

A

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