2. Electricity Flashcards
(85 cards)
1
Q
what are the 3 wire ( and there colours) in a plug
A
live - brown
neutral- blue
earth- green/yellow
2
Q
which wires are usually needed
A
live & neutral
3
Q
if something goes wrong which wire is used to stop you from getting hurt
A
earth wire
4
Q
what does the live wire do
A
alternates between a high +ve and -ve voltage of about 230 volts
= ac (alternating current - constantly changing direction)
5
Q
what voltage is the neutral wire always at
A
0 volts
6
Q
how does electricity flow through the live and neutral wire
A
flows in through the live wire and out through the neutral wire
7
Q
what are an earth wire and fuse ( or circuit breaker) used for
A
are just for safety
8
Q
definition of earthing
A
case must be attached to an earth wire
earthed conductor can never become live
9
Q
what kind of appliances must be earthed and why
A
all appliances with metal cases
redudces the danger of electric shock
10
Q
definition of double insulated
A
appliance with plastic casing and no metal parts showing
11
Q
what is plastic
A
an insulator
12
Q
definition of insulator
A
don’t conduct charge very well
stops a current flowing = can’t get a shock
13
Q
what does anything with double insulation not need
A
earth wire
only needs live and neutral earth wire
14
Q
what does earthing and fuses prevent
A
fires and shocks
15
Q
how does earthing and fuses prevent fires and shocks
A
- fault develops (live wire touches metal case)
- case is earthed= big current surges to earth
- this surge draws a large current through the live wire
- current melts (blows) fuse in live wire= cuts off live supply
- this isolates the appliance from the live= ipossible to get electric shock
- also prevents risk of large fire caused by heating effect of large current
16
Q
definition of circuit breaker
A
like fuses they protect the circuit from damage if to much current flows
17
Q
how does a circuit breaker work
A
- detect a surge in current in a circuit
2. break circuit by opening a switch
18
Q
how can a circuit breaker be more convenient than fuses
A
a circuit breaker ( and the circuit they are in ) can easily be reset by flicking a switch on the device
whereas fuses have to be replaced once they have melted
19
Q
definition of surge
A
sudden and great incease
20
Q
what does a current in a resistor result in
A
the electrical transfer of energy and an increase in temperature
21
Q
why does an electric current in a resistor cause energy transfer which heats the resistor
A
- electrons collide with the ions in the lattice which make up the resistor as the flow through it
- this gives ions energy = causes them to vibrate and heat up
22
Q
what does the heating effect of a resistor do
A
increase the resistors resistance = less current will flow or greater voltage will be needed to produce the same current
23
Q
how does the heating effect of a resistor work in a toaster
A
- toaster contain a coil of wire with really high resistance
- when current passes through coil = temp. increases
- temp increase= glows + give off infrared heat radiation = cooks bread
24
Q
equation for power
A
power = current x voltage
P = I x V
25
equation for energy transferred ( 1st one )
energy transferred = current x voltage x time
E = I x V x t
26
how many volts is UK main electricity
230 volts
27
definition a.c. supply
alternating current
| current is constantly changing direction
28
example of a.c. supply
mains electricity
29
definition of d.c. supply
direct current
| current keeps flowing in same direction
30
example of d.c. supply
cells and batteries
31
explain a series circuit
different components are connected in a line, end to end, between +ve and -ve power supply
(except for voltmeters which are always connected in parallel , but don't count as part of circuit )
32
what is special about a voltmeter ( in terms of circuits)
always connected in parallel
| don't count as part of a series circuit
33
why are series circuits not very handy
if you remove or disconnect one component = broken circuit = everything stops working
in practice very few thing connected in series
34
an example of something in a series circuit
fairy lights
35
explain a parallel circuit
each component is separately connected to the +ve and -ve of the supply
(except ammeters, which are always connected in series)
36
what is special about ammeters ( in terms of circuits)
always connected in series
37
what is good about parallel circuits
if you remove or disconnect 1 component it will hardly affect the others
38
examples of things in parallel circuits
cars and household electrics
39
how does a parallel circuit work for household electrics
each light switch in a house is part of a branch of a parallel circuit= just turns 1 light off on and off ( not all of them)
40
what does a current in series circuit depend on
applied voltage ( potential difference) and the nature of other components
41
when is there a bigger supply of potential difference in a series circuit
when more cells are in series ( all connected in same way)
eg. when 2 batteries with a potential difference on 1.5V are connected in series they supply 3V between them
42
what is the case for current in a series circuit
it is the same everywhere
43
what does the size of a current depend on
total potential difference (voltage ) and total resistance
I = V (total) / R (total)
44
what is the case for potential difference (p.d / voltage )in a series circuit
the total p.d is shared between components
the p.d for each component depends on its resistance
45
what is the case for total resistance in a series circuit
Total resistance = sum of the resistance of each component in the circuit ( R total = R 1 +R 2...)
depends on no. of components and type of components used
46
what is the case for p.d in a parallel circuit
p. d is the same across all branches
| eg. V 1 = V 2
47
what is the case for current in a parallel circuit
current is shared across the branches
eg. I (total) = I 1 + I 2
48
sketch typical current-voltage graphs for:
a. ) a wire ( at constant temp.)
b. a resistor ( at constant temp.)
c. ) a filament lamp
d. ) a diode
CGP pg.17
49
in a parallel circuit what does the current through a branch depend on
the resistance of the branch
50
in a parallel circuit the higher the resistance.... ( how does it effect the current )
higher resistance= harder it is for charge to flow= lower current ( in that branch)
if 2 identical components are connected in parallel = same current flows through each component
51
name 2 components which can change resistance
LDRs- light dependent resistor
| thermistor - temp. dependent resistor
52
describe how an LDR works
| be able to sketch graph
bright light = resistance falls
| darkness = resistance is highest
53
example of something that uses LDRs
useful device for various electronic circuits eg. burglar detectors
54
describe how a thermistor works
| be able to sketch graph
hot conditions= resistance drops
| cold conditions = resistance goes up
55
example of something that uses thermistors
make useful temperature detectors
eg. car engine temp. sensors
thermostats
fire alarms
56
definition of LEDs
light emitting diode
emits light when a current flows through it in the forward direction
57
examples of what LEDs are used for
digital clocks
traffic lights
remote controls
58
what is the advantage of LEDs compared to a light bulb
they don't have a filament which can burn out
59
what are LEDs and lamps used to indicate in a circuit
indicate the presence of a current in a circuit
| often used in appliances to show that they are switched on
60
what is the equation for voltage
voltage = current x resistance
V= I x R
61
definition of current
rate of flow of electrical charge
62
equation for charge
charge = current x time
Q = I x t
63
explain electric current in solid metallic conditions
flow of negatively charged electrons
64
what is a junction in a parallel circuit
where current is conserved
| current either splits of re-joins
65
why is current conserved at a junction
charge cant disappear or appear --- total current going into junction = total current leaving it
66
voltage across 2 components connected in parallel =?
the same
67
need to be able to calculate the currents, voltages and resistances of 2 resistive components connected in a series circuit
???
current = same
voltage = add
resistance = add
68
definition of voltage
energy transferred per unit charge passed
69
definition of volt
1 volt is 1 joule per coulomb
| voltage = energy transferred / charge
70
equation for energy transferred
energy transferred = charge x voltage
E = Q x V
71
PAPER 2
definition of electrical conductors + example
materials that conduct charge easily - a current can flow through them
eg. metals - copper + silver
72
PAPER 2
definition of electrical insulators + example
materials that don't conduct charge very well - so current cant flow
eg. plastic + rubber
73
PAPER 2
how are +ve and -ve electrostatic charges produced
by the movement of electrons
74
PAPER 2
how is a +ve electrostatic charge produced
loss of electrons
75
PAPER 2
how is -ve electrostatic charge produced
gain of electrons
76
PAPER 2
when do forces of attraction occur
between unlike charges
77
PAPER 2
when do forces or repulsion take place
between like charges
78
PAPER 2
how do you create (build ) a static charge
take 2 insulators and rub the vigorously together
| doesn't work with conductors
79
PAPER 2
what is the result of rubbing 2 insulators together
static charge
electrons scarped of one + dumped onto the other = +ve electrostatic charge on one + -ve on the other
80
PAPER 2
explain electrostatic phenomena
???PAPER 2
81
PAPER 2
what are the potential dangers of electrostatic charges
FRICTION TRANFERS ELECTRONS
eg. petrol pump= flowing petrol has friction = tranfers electrons= build static charge= spark = explosion
82
PAPER 2
how do you solve the dangers of electrostatic charges ( petrol pumps )
1. make pump out of metal
2. connected to earth
= electrons will conduct to earth as the charge transfer = larges cannot build
83
PAPER 2
what are the uses of electrostatic charges
1. photocopiers
| 2. ink jet printers PAPER 2
84
PAPER 2
how does electrostatic charge work in an inkjet printer
1. tiny droplets forced out fine nozzle = electrically charged
2. droplets deflected as pass between 2 metal plates
3. voltage applied to plate- one = -ve, the other +ve
4. droplets attracted to the plate of the opposite charge and repelled from the plate with the same charge
5. size + direction of voltage across each plate changes = each droplet deflected to hit a different place on the paper
6. loads of tiny dots make up printout
85
PAPER 2
how does electrostatic charge work in a photocopier
1. image plate = +ve charged
2. image of what copying projected onto it
3. whiter bits of what copying make light fall on plate = charge leaks away in those places
4. charged bits attract -ve charge black powder =transferred on to +ve charge paper
5. paper heated = powder sticks
6= photocopy of piece of paper
