electricity Flashcards
(103 cards)
1
Q
what is the current
A
the flow of electric charge around a circuit
2
Q
what is necessary for a current to flow around a complete circuit
A
a source of potential difference
3
Q
what is the value of the current in a closed loop
A
the current has the same value everywhere in the circuit
4
Q
what is potential difference
A
the driving force that pushes teh charge around
5
Q
what is the current measured in
A
Amps A
6
Q
what is the unit of potential difference
A
Volts V
7
Q
what is resistance
A
anything in the circuit that slows the flow down
8
Q
what is resistance measured in
A
Ohms
9
Q
what does the current flowing through a circuit depend on
A
depends on the potential difference across it and the resistance of the component
10
Q
draw cell
A
11
Q
draw battery
A
12
Q
draw switch open
A
13
Q
draw switch closed
A
14
Q
draw bulb
A
15
Q
draw fuse
A
16
Q
draw LED
A
17
Q
draw resistor
A
18
Q
draw variable resistor
A
19
Q
draw ammeter
A
20
Q
draw voltmeter
A
21
Q
draw diode
A
22
Q
draw LDR
A
23
Q
draw thermistor
A
24
Q
more charge passes around a circuit when there’s a ______ ______ _____
A
bigger current flow
25
what is an ohmic conductor
a component whose resistance does not change with the current
26
at a constant temperature what can he say about the relationship between an ohmic conductor and the potential difference across it
an ohmic conductor is directly proportional to the potential difference across it
27
examples of ohmic conductors
wire or resistor
28
examples of components where resistance does change with current
diode
filament lamp
29
what happens when a electrical charge flows through a filament lamp
it transfers energy to the thermal energy store,heating up the filament lamp
30
why does the resistance of a filament lamp increase as current increasesw
because the temperature of the filament lamp increases,raising resistance
31
how does the resistance in a diode depend on the current
it depends on the direction of the current
- high resistance if the current is reversed
32
what are some factors that the resistance of a circuit can depend on
- length of wire
- weather components are in a series or parallel circuit
33
what does a ammeter do
measures the current flowing through a circuit
34
what does a voltmeter do
measures the potential difference across a wire
35
where should the ammeter be placed
be placed in series with whatever your investigating
36
where should voltmeters be placed
in parallel around whatever your investigating
- NOT AROUND ANY OTHER BIT OF THE CIRCUIT
37
what is the practical to measure the effect of wire length on resistance
- attach crocodile clip to the wirelevel with 0cm on ruler
- attach second crocodile clip on wire e.g 10cm away from first clip - write down length of wire between them
- close switch and record pd + C
- open switch and move second crocidile clip down e.g annother 10cm
- close again and record,new wire length,pd+c
- repeat for a number of different lengths
- calculate the resistance for each length of wire
38
what are I-V characteristics
graphs which show how the current flowing through a component changes as the potential difference across it increased
39
what is an example of a linear component and what graph line will they have
straight line
ohmic conductor
40
what is an example of a non-linear component and what graph line will they have
curved line
filament lamp or a diode
41
what does the variable resistor do
controls the flow of electric current in a circuit by changing its resistance
42
what is a LDR
a resistor that is dependant on the intensity of light.
- in bright light resistance falls
- in darkness resistance is highest
43
what are the uses of LDRs
burglar detectors
automatic night lights
outdoor lighting
44
what is a thermistor
a temperature dependant resistor
- hot conditions resistance drops
- in cool conditions reistance increases
45
what are the uses of thermistors
useful temperature detectors like
car engine temperatures
thermostats
46
do the circuit signs quiz on cognito
47
what do sensing circuits do
they can be used to turn on or increase the power to components depending on the conditions that they are in
48
what is an example of a sensing circuit
a circuit used to operate a fan by using a thermistor and foxed resistor
49
how does a sensing circuit work in terms of a fan
- fixd resistor and fan will have same potential difference as they are parralell
- the potential difference is shared ebtween the components according to their resistances - bigger resistance more potential difference it takes
- as the room gets hotterthe thermistors resistance decreases so it takes a smaller share of potetinal difference, giving more to fan and fixed reistor making the fan go faster
50
how is a series circuit set up
the different components are connected in a line,end to end between the +ve and -ve of the power supply
- apart from voltmeters which connected in parallel but they dont count as apart of the circuit
51
what happens if you remove or disconnect one component in a series circuit?
the circuit is broken and all components stop
- generally not useful
52
if there are two cells in series circuit of a voltage of 1.5 what is the total supply
3 V
53
what is the current like in series circuits
the same current flows through all components
54
what is the size of the current determined by
the total potential difference of the cells and the total resistance of the circuit
55
how do you find the total resistance of two components in a series circuit
by adding up their resistances
56
what happens to the current when a resistor is added
the potential difference across each resistor is lower so the current between each resistor is also lower
- in series the current is the same everywhere so the total current is reduced when the resistor is added
- total resistance of circuit increases
57
how is a parallel circuit set up
- each component is separetley connected to the +ve and the -ve of the supply
- expect ammeters which are always connected in series
58
what is potential difference like in series circuots
its shared between the various components
59
what happens if you remove or disconnect a component in a parallel circuit
it will hardly affect the others
60
what is potential difference like in parallel circuits
its the same across all components
- identical bulbs connected in parallel will all have the same brightness
61
what is the current like in parallel circuits
its shared between the different loops
- by adding the current of each loop you will get the total loop
62
what happens when you add more components in a parallel series
the circuits total resistance will be lower
63
how can you investigate adding resistors in series circuits
- 4 identicle resistors
- build a circuit with a ammeter using one of the resistors
- make a note of the potential difference of the battery
- measure total the current using the ammeter and calculate the resistance
- add another resistor in series
- again measure total current and calucate resistance
- repeat last two setps untill all resistors have been added
64
how can you investigate adding resistors in parralell
- 4 identicle resistors
- build a circuit with a ammeter using one of the resistors
- make a note of the potential difference of the battery
- measure the total current using the ammeter and calculate the resistance
- add another resistor in parallel with the first
-again measure total current and calucate resistance
repeat last two setps untill all resistors have been added
65
what are the two types of electricty supplys
alternating current
direct current
66
what is happens in alternating current supplys
the current is always changing direction
67
how are alaternating currents produced
by alternating potential difference in which the positive and negative ends keep alternating
68
what tye of supply is the uk mains supply and at what volts
alternating current supply at 230 v
69
what is the frequency of the ac mains supply
50 cycles per second or 50v
70
what type of electricty do batterys and cells supply
direct current
71
what is direct current and what is it made by
- a current that always flows in the sane direction
- created by a direct potential difference
72
what are the three core cables of the mains supply built like
they have three wires inside of them each with a copper core and a coloured plastic coating
73
why do wires in mains supply have colours
to show its purpose
74
what colour is the live wire
brown
75
what does the live wire do and what is its potential difference
- provides the alternating current for mains supply
- pd = 230v
76
what colour is the neutral wire
blue
77
what does the neutral wire do and what is its potential difference
- it completes the circuit
- when appliance is operating normally the current flows through the live and neutral wire
-pd = 0
78
what colour is the earth wire
green and yellow
79
what does the earth wire do and what is its potential difference
- for protecting the wiring and for saftey
-stops the appliance casing from becoming live
- usually doesnt carry a current - only when theres a fault
pd - 0v
80
doe sthe earth wire carry a current
it usually doesnt only in the case of a fault
81
what is the potential difference of the body + earth
0v
82
what causes an electric shock
- the body like earth is at 0v
- when you touch a live wire a large potential difference is produced across you body and a current flows through you
- this causes a large electric shock which could injure or kill you
83
if a plug or switch is turned off how is there still there still a danger of an electric shock.
the current isnt flowing but there is still a pd in the live wire so if you made contact with the live wire your body would provide a link between the wire and the earth,so the current would flow through you
84
how do kettles transfer energy electrically
they transfer energy electrically from the mains ac supply to the thermal energy store of the kettle
85
how do fans transfer energy electrically
they transfere energy electrically from the battery of a handheld fan to the kinetic energy store of the motor
86
what does the total energy transferred by an appliance depend on
how long its on for
its power
87
what does the power rating tell you
the maximum amount of energy transferred between stores per setting when the appliance is in use
88
how does the power rating help customers choose between models
the lower the power rating the less electricity the appliances uses in a given time so its cheaper to run
89
does higher power mean better performance in appliances
not necessarily - it might transfer the same amount of energy usefully, transferring more but wasting more as well
90
how is electricity distributed in britain
via the national grid
91
what is the national grid
a giant system of cables and transformers that covers the uk and connects power stations to consumers
92
how does that national grid transfer electrical power
it transfers power from power stations anywhere on the grid to anywhere else of the grid where its needed
93
why do power stations ahve to change the amount of electricty the produce
to meet demands throughout the day
94
when does electricty demand usually increase
- in the morning
- in the evening when people come home from school or work
- when it gets dark and cold outside
95
what can cause a sudden spike in electricity demand
popular events on tv - like sports events
96
why do power station usually run below maximum capacity
to handle unexpected spikes in demand or failures at other stations
97
what role do smaller power stations play in managing electricity demand
they are kept on standby to start quickly when needed
98
what do you need to trasmit a huge amount of power
a high potential difference or high current
99
what is the problem with using a high current to transmit power
it causes the wires to heat up,losing energy to the thermal store of the surrondings
100
why is a high potential difference preffered in the antional grid
its cheaper to boost the potential difference up really high (up to 400000V)
101
what is needed to get the potetinal difference of the national grid up to 400000V
it requires big transformers as well as big plysons with huge isnulators
102
how do transformers help increase the potential difference on the national grid
- the transformers have to set the potential difference up at one end for useful transmission and then bring ti back down fro safe usable levels on the other end
- potential diffference in increased at step up using a step up trasnformer
- potential difference is decreased for domestic used using a step down transformer
103
what can we assume if transformers are almost 100% useful
that the power input is equal to the output power
