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Physics GCSE > topic 10 - electricity and circuits > Flashcards

topic 10 - electricity and circuits Flashcards

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1
Q

current

A

the flow of electric charge around the circuit/

the rate of flow of charge

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2
Q

what is current measured in and how

A

measured in Amperes (A)

measured using an ammeter connected in series

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3
Q

what is current in metals and how does it flow

A

current in metals is the FREE FLOW OF ELECTRONS
atoms in metals are bonded into a lattice of positive ions surrounded by a sea of delocalised electrons - these free electrons are free to move through the whole metal

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4
Q

potential difference/voltage

A

the energy transferred per unit of charge

the driving force that pushes the change around

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5
Q

what is voltage measured in and how

A

measured in volts (V)

measured using a voltmeter connected in parallel

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6
Q

resistance

A

anything that slows down the flow of charge

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7
Q

what is resistance measured in

A

Ohms (Ω)

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8
Q

charge, current, time relationship

A

charge = current x time

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9
Q

energy transferred, charge, p.d relationship

A

energy transferred = charge x potential difference

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10
Q

p.d, current, resistance relationship

A

potential difference = current x resistance

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11
Q

why does a resistor heat up as current flows through it (general)

A

when charge flows through a component, it must do work against resistance
this causes an electrical transfer of energy
some of this is transferred usefully but some is dissipated to the thermal energy stored of the component and the surroundings

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12
Q

why if a resistor is too hot can current not flow through it (atomic level)

A

electrons collide with ions in the lattice as they flow through, giving the ions energy and causing them to vibrate more
the more the ions vibrate, the harder it is for electrons to travel through so for a given p.d current decreases as the resistor heats up

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13
Q

what do low resistance wires do

A

reduce energy dissipated to thermal stores as the current flows between components

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14
Q

how to investigate the relationship between current potential difference and resistance for a range of components - describe circuit

A

a circuit connecting an ammeter, component and variable resistor in series and a voltmeter in parallel to the component

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15
Q

how to investigate the relationship between current potential difference and resistance for a range of components - process (5)

A

1) set resistance of variable resistor
2) measure current and potential difference across the component
3) repeat at lots of different resistances
4) swap over the wires to reverse the direction of the current, so the ammeter will give negative readings and repeat
5) plot results on I-V graphs

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16
Q

what do I-V graphs show

A

show how current changes as potential difference is changed

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17
Q

linear components

A

components which show a straight line I-V graph

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18
Q

non-linear components

A

components which have a curved line I-V graph

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19
Q

the steeper the I-V graph….

A

the lower the resistance

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20
Q

what is the relationship between variables for a fixed resistor

A

current is directly proportional to p.d

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21
Q

what is the I-V graph like for a filament lamp

A

increasing current, increases the temperature of the filament, increasing resistance so the graph is curved

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22
Q

what is the I-V graph like for a diode

A

current only flows through a diode in one direction, the diode has very high resistance in the opposite direction

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23
Q

light dependent resistor (what lowers resistance)

A

the brighter the light, the lower the resistance

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24
Q

thermistor (what lowers resistance)

A

the warmer it is, the lower the resistance

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25
Q

how to investigate how the resistance of an LDR changes with brightness (5)

A

1) conduct experiment in a dim room
2) measure p.d across and current through the LDR
3) change the light level near the LDR
4) measure p.d and current again for a range of light levels
5) calculate resistance for each measurement using (resistance = voltage/ current)

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26
Q

how to investigate how the resistance of a thermistor changes with temperature (4)

A

1) measure the p.d across and current through the thermistor
2) change temperature of thermistor by heating it
3) measure the p.d and current again for a range of temperatures
4) calculate resistance for each measurement using (resistance = voltage/current)

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27
Q

series circuit

A

different components are connected end to end in a line between the positive and negative of a power supply (excluding voltmeters which are always connected in parallel)

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28
Q

what happens if one component breaks or is removed in a series circuit

A

the whole circuit breaks and stops working

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29
Q

rules in a series circuit (4)

A
  • current is the same everywhere
  • voltage from cells adds up to give total p.d
  • total p.d is shared between components according to its resistance (the greater the resistance, the greater the p.d)
  • resistance is added up to give total resistance
30
Q

parallel circuit

A

each component is connected separately to the negative and positive of the power supply (apart from ammeters which are always connected in series)

31
Q

what happens if one component breaks or is removed in a parallel circuit

A

the other components are hardly affected

32
Q

rules in a parallel circuit (5)

A
  • current is shared between branches
  • at junctions where current splits or rejoins the total current going into the junction equals the current leaving it
  • if two identical components are connected in parallel, the same current will flow through each component
  • p.d is the same across all components
  • if you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors
33
Q

why is the total resistance in a series circuit the sum of all the components’ resistances

A

by adding a resistor in series, the two resistors have to share the p.d
the p.d across each resistor is lower, so the current through each resistor is lower
the current is the same everywhere so the total current in the circuit is reduced when a resistor is added
this increases the total resistance of the circuit

34
Q

how can you investigate the effect of increasing resistance on current IN A SERIES CIRCUIT (6)

A
  • need 4 identical resistors
  • build a series circuit with an ammeter, a resistor and battery (make a note of its p.d)
  • measure the current using the ammeter and calculate the resistance of the whole circuit
  • add another resistor in series, measure current and calculate resistance
  • repeat until all resistors have been used
  • plot a graph of number of resistors against total resistance
35
Q

why if you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors?

A

in parallel, there is the same p.d
by adding another loops, the current has more than one direction to flow it, increasing the total current that can be flowing in the circuit
using voltage = current x resistance, an increase in current means a decrease in the total resistance of the circuit

36
Q

how can you investigate the effect of increasing resistance on current IN A PARALLEL CIRCUIT (6)

A
  • need 4 identical resistors
  • build a series circuit with an ammeter, a resistor and battery (make a note of its p.d)
  • calculate resistance of the whole circuit
  • add another resistor in parallel and measure total current through the circuit, using it to calculate total resistance
  • repeat until all resistors have been added
  • plot a graph of number of resistors against total resistance
37
Q

energy is transferred in an electrical circuit when…

A

an electrical charge goes through a change in potential difference

38
Q

energy (J) =

A

current (A) x potential difference (V) x time (s)

39
Q

what is energy supplied for

A

supplied to raise the charge through a potential

the charge gives up the energy at any potential drop at components elsewhere in the circuit

40
Q

energy transfer in circuits (+note on efficiency)

A

energy is transferred from cells to components in a circuit when current flows
no appliance is completely efficient ; the higher the current, the more energy is transferred to the thermal energy stored of the components and then to the surroundings (heating usually increases with the resistance of components)

41
Q

fuses

A

protect circuits by melting and breaking the circuit if the current gets too high

42
Q

how can heating in circuits be beneficial in terms of heating

A

in toasters, there is a high resistance coil that once current is flowing through it, heats up so much that it glows and gives off infrared radiation, cooking the bread
(this also works in filament lamps and electric heaters)

43
Q

power of appliance

A

the energy it transfers per second

44
Q

what is power measured in

A

Watts (W)

45
Q

power rating

A

the maximum safe power for operation (MAXIMUM OPERATING POWER)

46
Q

relationship , power, energy, time

A

power = energy / time

47
Q

relationship ; power, current, p.d

A

power = current x potential difference

48
Q

relationship ; power, current, resistance

A

power = current^2 x resistance

49
Q

what is a.c used as

A

the mains supply

50
Q

what is UK mains supply p.d and frequency

A

230V

50Hz

51
Q

what is d.c used as

A

to transfer energy from cells and batteries

52
Q

wires

A

have a copper core and an insulatory coloured plastic coating

53
Q

what are 3 wires

A

neutral wire blue
live wire brown
earth wire green and yellow

54
Q

neutral wire blue

A

completes the circuit

55
Q

live wire brown

A

carries the voltage

56
Q

earth wire yellow and green

A

for safety and protecting the wiring
carries the current away if something goes wrong
stops the appliance casing from becoming live

57
Q

p.d between live and neutral

A

230V

58
Q

p.d between live and earth for mains connected appliance

A

230V

59
Q

p.d between earth and neutral

A

0V

60
Q

how does electricity flow through a plug

A

flows in through the live wire

flows out through the neutral wire

61
Q

why can you get an electric shock

A

the body rests at 0V
if you touch a live wire, a large potential difference is produced across your body and current flows through you, causing an electric shock that could injure or kill you

62
Q

surge

A

sudden increase in current

63
Q

what can cause surges

A

changes in a circuit

fault in the electrical appliance

64
Q

what can a surge result in

A

circuits and wiring melting

causing a fire

65
Q

what can faulty appliances lead to

A

deadly electric shocks

66
Q

what are used to prevent electric shocks or surges from harming others

A

an earth wire and a fuse

67
Q

if the live wire in a toaster touches the metal casing what happens

A

the toaster has become faulty
this causes a current surge as current flows in though the live wire, through the casing and out down the earth wire
the surge causes the fuse to melt
this breaks the circuit and cuts off the live supply
the whole appliance is now isolated and it is impossible to get an electric shock from the case

68
Q

circuit breaker

A

even safer than fuses
instead of melting, a large current will ‘trip’ a circuit breaker
they turn off quicker than how long it takes for a fuse to melt
can easily be reset but are more expensive

69
Q

role of insulation of electrical appliances

A

appliances with metal casing should be ‘earthed; to reduce the danger of electric shock
a plastic casing can’t conduct so can’t become live

70
Q

double-insulated appliance

A

an appliance with a plastic casing and no metal parts showing

71
Q

what wires does a double-insulated appliance have

A

the two core cables (neutral blue and brown live)

it doesn’t need an earthing wire

Physics GCSE (10 decks)

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