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
2
Q
Describe what is meant by a magnetic field
A
A region in which a magnetic pole experiences a force
3
Q
Which way do magnetic field lines point
A
Direction of force of N pole
4
Q
What is produced if a bar magnet is cut in half
A
Two magnets, each with N pole and S pole
5
Q
What are the magnetic materials
A
- nickel
- cobalt
- iron
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
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
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
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
10
Q
What types of charges are there
A
Positive and negative
11
Q
Describe electrostatic charging by friction
A
- transfer of electrons
- gain electrons: negative
- lose electrons: positive
12
Q
Measurements for charge
A
In coulombs (Q)
13
Q
Describe what is meant by an electric field
A
Region in echo an electric charge experiences a force
14
Q
Direction of electric field
A
Direction of force on positive charge
15
Q
Define electric current
A
The charge passing a point per unit time
16
Q
Define electric current
A
Charge passing a point per unit time
17
Q
Equation for charge
A
I = Q/t
18
Q
Describe electrical conduction in metals
A
- movement of delocalised electrons
- carry negative charge
19
Q
Direction of conventional current
A
Positive to negative
20
Q
Direction of flow of electrons
A
Negative to positive
21
Q
Difference between alternating/direct current
A
Moving charges continuously change direction // moving charges flow in one direction only
22
Q
Define electromotive force
A
- electrical work done by a source
- in moving a unit charge around a complete circuit
23
Q
Units for electromotive force
A
Volts (V)
24
Q
How is voltage distributed in series circuit
A
Shared between components
25
Define potential difference
- work done by unit charge
- passing between 2 points in a circuit
26
Units for potential difference between 2 points
Volts (V)
27
Equation for resistance
R = V / I
28
Relationship between resistance and wire length
Directly proportional
29
Relationship between resistance and cross sectional area of wire
Inversely proportional
30
Current-voltage graph for resistor with constant resistance
31
Current-voltage graph for resistor with constant resistance
32
Unit for electrical resistance
Ohms (Ω)
33
what do electric circuits do
- transfer energy from source of electrical energy (eg electrical cell, mains supply)
- to circuit components and then into surroundings
34
equation for electrical power
35
equation for electrical energy
36
equation for energy in kilowatt hours
power (kW) * time (hours)
37
electrical symbol for cells
38
function of electrical cells
- provide direct current
- store of energy
39
electrical symbol for batteries
40
function of batteries
- series of cells
- larger store of energy than one cell
41
electrical symbol for ac power supply
42
function of ac power supply
- provide ac current
- store of energy
43
electrical symbol for dc power supply
44
function of dc power supply
- provide dc current
- store of energy
45
electrical symbol for switch
46
function of switch
- open/close circuit
- turn devices on/off
47
electrical symbol for fixed resistor
48
function of fixed resistor
- resists flow of electrons
- limits current
49
electrical symbol for variable resistor
50
function of variable resistor
- changes resistance and thereby changes current
- dimmer switches
51
electrical symbol for heaters
52
function of heaters
- transfer electrical energy to thermal energy
- heats room/space
53
electrical symbol for lamps
54
function of lamps in circuit
- transfers energy into light
- lighting
55
electrical symbol for motors
56
function of motor in circuit
- use current to make spinning motion
- store of kinetic energy
57
electrical symbol for ammeter
58
function of ammeter in circuit
- measures current
58
electrical symbol for voltmeter
59
function of voltmeter in circuit
- measures potential difference
59
electrical symbol for fuses in circuit
60
function of fuses in circuit
- breaks circuit if too much current
- safety device
61
electrical symbol for generators
62
function of generators in circuit
- use kinetic energy to produce current
- generate electricity
63
electrical symbol for light-emitting diodes (LEDs)
64
function of LEDs in circuit
- emits light of specific colour when current flows
- low energy lighting
65
does current change in series circuit
no
66
how to place LED symbol in circuit diagram
place arrow facing conventional current
67
does current flow both ways in LED
no, only one
68
relationship between combined pd and emf in series circuits
sum of pd across resistors equal to battery power (emf)
69
how to calculate combined resistance of resistors in series
add them up
70
relationship between sum of currents entering junction in parallel circuit and leaving junction
equal
71
relationship between pd across components in series circuits and sum of individual pd across each component
equal
72
relationship between pd across each branch of parallel arrangement of components and pd of whole arrangement
equal
73
advantages of connecting lamps in parallel in a circuit
- pd across each lamp in parallel equally bright
- brighter
74
how does current change at junction of parallel circuit
branches off
75
how to calculate resistance in parallel circuits
76
how is combined resistance of 2 resistors in parallel diff to either resistor by itself
resistors in parallel have less resistance than the one on its own
77
describe heating effect of current
current increases, heat increases
78
electrical hazards include:
- damaged insulation
- overheating cables
- damp conditions
- excess current from overloading of plugs, extension leads, single and multiple sockets when using mains supply
79
hazards of damaged insulation (electricity)
- if insulation damaged and exposed live wire touched
- will be electrocuted
80
hazards of overheating cables
- large current flow thru appliance
- causes it to heat up
- can potentially cause fire
81
hazards of damp conditions (electrical safety)
- water conducts electricity
- can be electrocuted by simply touching electrical appliance when wet, or when hands wet
82
hazards of excess current from overloading of plugs, extension leads, single and multiple sockets when using mains supply
- draw too much current thru one socket
- overloads socket
- may result in fire
83
what are the main safety devices in electrical appliances
- earthing/non-conducting metal cases
- fuses
- trip switches
84
use and operation of trip switches
- 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
use and operation of fuses
- 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
fuse ratings and use?
- rating must be lowest value
- which is greater than amount of current appliance designed to use
87
how do earthing metal cases work
- 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
what items required to make an electromagnet
- coil of wire
- power supply
89
how can an emf be induced across a conductor
- conductor moving across a magnetic field
- changing magnetic field linking with a conductor
90
factors affecting magnitude of an induced emf
- force/speed at which magnet/wire moved
- strength of magnet
91
describe a simple form of a.c. generator
- 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
p4.5.2??
