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Physics GCSE > Section 5 - Current and Circuits > Flashcards

Section 5 - Current and Circuits Flashcards

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1
Q

What is current?

A

The flow of electric charge around the circuit

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2
Q

What is the charge equation?

A 
Charge = Current x Time
Coulombs = Amps x Seconds
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3
Q

A battery passes a current of 0.25A through a light bulb over a period of 4 hours
How much charge does the battery transfer altogether?

A 
Q = C x T
Q = 0.25 x 4(60x60)
Q = 3600C
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4
Q

Calculate how long it takes a current of 2.5A to transfer a charge of 120C

A 
Q = C x T
T = Q / C
T = 120 / 2.5
T = 48s
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5
Q

What is potential difference?

A

The energy transferred per coulomb of charge

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6
Q

What is the energy transferred equation?

A 
Energy = Charge x Potential Difference
Joules = Coulombs x Volts
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7
Q

What is the potential difference equation?

A 
Voltage = Current x Resistance
Volts = Amps x Ohms
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8
Q

A 4 ohm resistor in a circuit has a potential difference of 6.0 V across it
What is the current through the resistor?

A 
V = I x R
I = V / R
I = 6 / 4
I = 1.5 A
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9
Q

What does resisitance often cause?

A

An increase in temperature

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10
Q

Why does resisitance increase heat?

A

When the electrons collide with the ions in the lattice that make up the resistor the ions gain energy which causes them to heat

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11
Q

Give one exception where resistance decreases with heat?

A

Thermistor

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12
Q

What usually happens when the resistor gets too hot?

A

No current will be able to flow

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13
Q

A current flowing through a resistor transfer 360 J of energy when 75 C of charge are passed through it
Calculate the PD across the resistor

A 
E = Q x V
V = E / Q
V = 360 / 75
V = 4.8 V
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14
Q

What does a standard test circuit include?

A

Ammeter
Energy Source (eg. Battery)
Voltmeter
Component

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15
Q

How do you use a standard test circuit?

A

Change the voltage and make readings from the ammeter and voltmeter and plot graph

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16
Q

When testing the standard test circuit, what must you stop from happening?

A

The circuit getting too hot as it will affect results

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17
Q

What does a diode do?

A

Acts as a one-way switch for the current

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18
Q

What should you see when investigating thermistors?

A

As you heat the thermistor, the current through the thermistor increases as the resistance decreases

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19
Q

What should you see when investigating LDR’s?

A

As the light gets brighter, the current increases as the resistance decreases

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20
Q

Describe a resistor IV graph?

A

Directly proportional

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21
Q

Describe a wire IV graph?

A

Directly proportional

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22
Q

Describe a filament IV graph?

A

S shape

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23
Q

Describe a diode IV graph?

A

Exponential in one direction (curver above x axis only)

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24
Q

What are linear components?

A

Components that have an IV graph that’s a straight line

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25
Q

What are non-linear components?

A

Components that have an IV graph that is curved

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26
Q

How do LDRs affect resistance?

A

In bright light the resistance falls, in darkness the resistance is highest

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27
Q

What are LDRs used in?

A

Automatic night lights
Outdoor lighting
Burgular detectors

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28
Q

How do thermistors affect resistance?

A

In hot conditions the resistance drops, in cool conditions the resistance goes up

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29
Q

What are thermistors used in?

A

Temperature detectors
Car Engine sensors
Thermostats

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30
Q

Describe a series circuit?

A

A circuit of components connected in a line, end to end

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31
Q

What is wrong with a series circuit?

A

IF you remove, break or disconnect one component the circuit will stop

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32
Q

What are the rules behind a series circuit?

A

The current is the same everywhere
The voltage is shared between the componenets
The total resistance increases as you increase resistors

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33
Q

Describe a parallel circuit?

A

A circuit of components where they are separately connect

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34
Q

What are always connected in series?

A

Ammeters

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35
Q

What are the rules behind a parallel circuit?

A

The voltage is the same across all components
The current is shared between he branches
The total resistance of the circuit decreases if you add a second resisitor in parallel

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36
Q

A filament lamp and a resistor are connected in series
A current of 0.5A flow through the lamp
State the current flowing through the resisitor?

A

0.5 A

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37
Q

What happens in series when you add resistors?

A

The total resistance increases

38
Q

Why does the resistance of a series circuit increase when you add resistors?

A

The voltage is being shared across more components, so there will be lower voltage through each resistor therefore the current will also be lower

39
Q

What happens in parallel when you add resistors?

A

The total resistance decreases

40
Q

Why does the resistance of a parallel circuit decrease when you add resistors?

A

Another loop will be added therefore the current will have an extra way to go which means the total current will increase therefore there will be a decrease in the total resistance

41
Q

A 12V cell is connected in series with a 2ohm resistor, a 3ohm resistor and a 7ohm resistor
Calculate the current going through

A 
V = I x R
I = V / R
I = 12 / (3+2+7)
I = 12 / 12
42
Q

What happens when an electrical charge goes through a change in potential difference?

A

Energy is transferred

43
Q

Why is energy transferred when a charge changes voltage?

A

Work is done against resistance

44
Q

What is the energy transferred equation?

A 
E = I x V x t
Energy = Current x Voltage x Time
45
Q

What do fuses do?

A

Protect the circuits by melting if the current gets too high

46
Q

How can heating from a circuit be good?

A

In toasters/bulbs/heaters, where a extremely resistant coil has electricity passed through it which gives off infrared radiation

47
Q

A laptop charger is connected to a 230 V source for an hour
A current of 8.0 A flows through it
Calculate the energy transferred by the laptop charger

A 
E = I x V x t
E = 8 x 230 x (60x60)
E = 6,624,000 J
48
Q

What does energy transferred depend on?

A

How long the appliance is in for and its power

49
Q

What is the power equation?

A

Power = Energy / Time

50
Q

Which transfers more energy in the same time?
A 500W microwave
A 750W microwave

A

The 750W microwave

51
Q

What is the voltage of a charge?

A

The amount of energy each unit of charge transfers

52
Q

What is the power equation (IV)

A 
P = I x V
Power = Current x Voltage
53
Q

A 1 kW hair dryer is connected to a 230V supply

Find the fuse needed?

A 
P = I x V
P / V = I
1000 / 230 = I
4.3 A 
therefore a 5 A fuse is needed
54
Q

What is the power equation (IR)?

A 
P = I² x R
Power = Current² x Resistance
55
Q

Calculate the difference in the amount of energy transferred by a 250 W TV and 375 W TV when they are both use for two hours?

A 
P = E / t
250 x (2x60x60) = E1
1,800,000 = E1
375 x (2x60x60) = E2
2,700,000 = E2
E2 - E1 = 900,000
56
Q

What is AC?

A

Movement of charge in a constantly changing direction

57
Q

What produces alternating currents?

A

Alternating voltages

58
Q

What is the voltage inside the house?

A

230V

59
Q

What is the frequency of the house AC?

A

50Hz

60
Q

What supply direct current?

A

Batteries and cells

61
Q

What creates DC?

A

Direct Voltage

62
Q

What colour is the live wire?

A

Brown

63
Q

What is the live wire

A

The wire that carries the voltage

64
Q

What colour is the neutral?

A

Blue

65
Q

What is the neutral wire?

A

The wire that completes the circuit

66
Q

What is the voltage of the blue wire?

A

0V

67
Q

When does the blue wire have a current?

A

When the appliance is working normally

68
Q

What colour is the earth wire?

A

Green and yellow

69
Q

What is the earth wire?

A

The wire for safety and protection

It carries the current away if something goes wrong

70
Q

What is the voltage of the earth wire?

A

0V

71
Q

What is the voltage of the live wire?

A

230V

72
Q

Explain the difference between a.c and d.c electricity supplies?

A

In AC the movement of the charges constantly changes whilst in a direct current supply the movement of the charges is only in one direction

73
Q

What do earthing and fuses prevent?

A

Electrical overloads

74
Q

What can current surges lead to?

A

Melting, fire or electric shocks

75
Q

What is a fault?

A

Where the live wire touches the metal case

76
Q

What do circuit breakers do?

A

Instead of melting, a large current simply shuts it off

77
Q

What are the advantages of circuit breakers?

A

Can be reused and much quicker than fuses

78
Q

What are the disadvantages of circuit breakers?

A

Expensive

79
Q

What doesn’t need an earth wire?

A

A double insulated appliance

80
Q

Which wire are fuses connect to?

A

The Live wire

81
Q

Name one linear component and one non-linear component?

A

Resistor and diode

82
Q

What happens to the resistance of a thermistor as it gets hotter?

A

It decreases

83
Q

How does the current in each component differ?

A

Based off the resistance in the components

84
Q

How does potential difference vary in parallel?

A

Total amount shared inside each branch

85
Q

How does adding resistors in parallel affect the resisitance?

A

It decreases it

86
Q

Give two disadvantages of the heating effect?

A

Inefficient and can break circuit

87
Q

Give two advantages of the heating effect?

A

Can be made into useful energy (bulb or heater) and can be used in fuse

88
Q

What is a power rating

A

The power that flows through the componenet

89
Q

Why are the three wires in a three-core cable coloured?

A

Avoid confusion which could lead to shocks

90
Q

Give the potential difference for the three wires?

A

Live - 230 V
Neutral - 0 V
Earthed - 0 V

91
Q

Explain why touching a live wire is dangerous?

A

The wire has 230 V which will flow through you to reach earth

92
Q

Explain how a fuse works?

A

If the current gets too hot, the temperature will increase and melt the fuse, stopping the circuit from working

Physics GCSE (8 decks)

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