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Physics Unit 1 > Electricity > Flashcards

Electricity Flashcards

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1
Q

What happens when you rub two different insulating materials against each other?

A

They become electrically charged. This only works for insulated objects.

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2
Q

List four things which happen when different insulating materials are rubbed against each other.

A
  • Negatively charged particles called electrons move from one material to the other
  • The material that loses electrons becomes positively charged
  • The material that gains electrons becomes negatively charged.
  • Both materials gain an equal amount of charge, but the charges are opposite.
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3
Q

When will charged objects repel each other?

A

Two charged objects will repel each other if they have the same type of charge (both positive or negative).

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4
Q

When will charged objects attract each other?

A

Two charged objects will attract each other if they have opposite charges

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5
Q

How can you tell whether or not an object is charged?

A

The only way you can tell is to see if it repels another charged object. This is because charged objects will also attract small uncharged objects.

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6
Q

How can electrical circuits be represented?

A

Electrical circuits can be represented by circuit diagrams

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7
Q

How are various electrical components shown?

A

The various electrical components are shown by using standard symbols in circuit diagrams.

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8
Q

How can components be connected?

A

Components can be connected in series, or parallel circuits. The characteristics of the current and potential difference (voltage) are different in series and parallel circuits.

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9
Q

What two things are important for a circuit to work?

A

There must be a complete circuit and there must be no short circuit.

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10
Q

How do you check for a complete circuit?

A

Follow a wire coming out of the battery with your finger. You should be able to go out of the battery, through the lamp, and back to the battery.

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11
Q

How do you check for a short circuit?

A

To check for a short circuit, see if you can find a way past the lamp without going through any other component. If you can then there is a short circuit and the lamp will not light.

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12
Q

What is electric current?

A

Electric current is a flow of electric charge. No current can flow if the circuit is broken - for example, when a switch is open.

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13
Q

How is current measured?

A

Current is measured in amperes (which is often abbreviated to amps or A).

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14
Q

How is current flowing through a component in a circuit measured?

A

The current flowing through a component in a circuit is measured using an ammeter. This must be connected in series with the component.

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15
Q

The size of an electric current is the rate of flow of electric charge. You can calculate the size of a current using this equation:

A 
I=Q divided by t
I= The current in amperes (amps), A
Q= The charge in coulombs, C
t= The time in seconds, s
For example, what is the current if 20C of charge passes in 5s?
Current= 20 divided by 5 = 4A
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16
Q

What is potential difference needed for?

A

A potential difference, also called voltage, across an electrical component is needed to make a current flow through it. Cells or batteries often provide the potential difference needed.

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17
Q

What is potential difference measured in?

A

It is measured in volts, V. The potential difference across a component in a circuit is measured using a voltmeter. This must be connected in parallel with the component.

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18
Q

The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points. You can calculate the size of a potential difference using this equation:

A

V=W divided by Q
V is the potential difference in volts, V
W is the work done (energy transferred) in joules, J
Q is the charge in coulombs, C
For example, what is the potential difference if 48J of energy is transferred when 4C of charge passes?
Potential difference= 48 divided by 4 - 12V

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19
Q

What happens when two or more components are connected in series?

A

When two or more components are connected in series, the same current flows through each component.

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20
Q

What is resistance measured in?

A

Resistance is measured in ohms.

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21
Q

How is resistance calculated?

A

It can be calculated from the potential difference across a component and the current flowing through it.

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22
Q

What is the total resistance of a series circuit?

A

The total resistance of a series circuit is the sum of the resistances of the components in the circuit.

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23
Q

What does the resistance of thermistors depend on?

A

The resistance of thermistors depends on the temperature while the resistance of light-dependant resistors (LDR’s) depends on the light intensity.

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24
Q

When does the resistance in a wire increase?

A

The resistance in a wire increases as:

  • The length of the wire increases
  • The thickness of the wire decreases
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25
Q

What makes it more difficult for the electric current to flow, and cause resistance?

A

An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal.

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26
Q

Why is the resistance of a long wire greater than it is for a short wire?

A

The resistance of a long wire is greater than the resistance of a short wire because electrons collide with ions more often

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27
Q

Why is the resistance of a thin wire greater than it is for a thick wire?

A

The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current.

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28
Q

How can the resistance of a component be found?

A

The resistance of a component can be found by measuring the current flowing through it, and the potential difference across it.

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29
Q

This equation shows the relationship between potential difference, current and resistance:

A

V = I x R
V is the potential difference in volts, V
I is the current in amperes (amps), A
R is the resistance in ohms, Ω
The equation can be rearranged to find the resistance:
R = V divided by I
For example, 3A flows through a 240V lamp. What is the resistance of the lamp?
Resistance = 240 divided by 3 = 80Ω

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30
Q

What does a graph of current against potential show you?

A

A graph of current against potential difference shows you how the current flowing through a component varies with the potential difference across it.

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31
Q

What is a filament lamp?

A

The filament lamp is a common type of light bulb.

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32
Q

What does a filament lamp contain?

A

It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.

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33
Q

When does an electric current flow?

A

An electric current flows when electrons move through a conductor, such as a metal wire.

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34
Q

What happens if the moving electrons collide with the ions in the metal?

A

It makes it more difficult for the (electric) current to flow, and causes resistance.

35
Q

What can increase the resistance?

A

As the temperature increases, the metal ions vibrate more. There are more collisions with the electrons and so the resistance increases.

36
Q

What are diodes?

A

Diodes are electronic components which can be used to regulate the potential difference in circuits and to make logic gates.

37
Q

What does LED stand for?

A

Light-emitting diode

38
Q

What do LED’s produce?

A

A light-emitting diode, LED, produces light when a current flows through it in a forward direction.

39
Q

What are LED’s often used for?

A

LED’s are often used for indicator lights in electrical equipment such as computers and TV sets.

40
Q

Why is the use of LED’s increasing?

A

As LED’s use a smaller current than other types of lighting, their use is increasing.

41
Q

What are thermistors used as?

A

Thermistors are used as temperature sensors - for example in fire alarms.

42
Q

What happens to the resistance of a thermistor at low temperatures?

A

At low temperatures, the resistance of a thermistor is high and little current can flow through them.

43
Q

At high temperatures, what happens to the resistance of a thermistor?

A

At high temperatures, the resistance of a thermistor is low and more current can flow through.

44
Q

In the dark and at low light levels, what happens to the resistance of an LDR?

A

In the dark and at low light levels, the resistance of an LDR is high and little can flow through it.

45
Q

In bright light, what happens to the resistance of an LDR?

A

In bright light, the resistance of an LDR is low and more current can flow through it.

46
Q

What is the UK mains electricity supply (V and Hz)?

A

The UK mains electricity supply is about 230V at 50Hz. It can kill if not used safely.

47
Q

What are electrical circuits, cables, plugs and appliances designed to reduce?

A

They are designed to reduce the chances of receiving an electric shock.

48
Q

What is ‘direct current’?

A

If the current flows in only one direction it is called direct current (DC).

49
Q

List two things which supply DC electricity.

A

Batteries and cells supply DC electricity, with a typical battery supplying around 1.5V

50
Q

What is ‘alternating current’?

A

If the current constantly changes direction, it is called alternating current (AC).

51
Q

Name one thing which supplies AC electricity.

A

Mains electricity is an AC supply, with the UK mains supply being about 230V. It has a frequency of 50Hz (50 hertz), which means it changes direction, and back again, 50 times a second.

52
Q

What does a mains electricity cable contain?

A

Two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical conductor. The inner wires are colour coded.

53
Q

What are the colours of the three inner wires within a cable?

A

Blue - Neutral
Brown - Live
Green and yellow stripes - Earth

54
Q

List 5 features of a plug

A
  • The case is made from tough plastic or rubber, because these materials are good electrical insulators.
  • The three pins are made from brass, which is a good conductor of electricity.
  • There is a fuse between the live terminal and the live pin.
  • The fuse breaks the circuit if too much current flows.
  • The cable is secured in the plug by a cable grip. This should grip the cable itselg=f, and not the individual wires inside it.
55
Q

Where does each wire go (inside a plug)?

A

There is an easy way to remember where to connect each wire.
bLue goes Left
bRown goes Right
sTriped goes to the Top.

56
Q

What do fuses protect?

A

Fuses protect electrical circuits and appliances.

57
Q

When will the fuse break the circuit?

A

The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong.

58
Q

What do fuses contain?

A

The fuse contains a piece of wire which melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.

59
Q

What do circuit breakers protect?

A

Circuit breaks also protect electrical circuits and appliances.

60
Q

What do residual current circuit breakers (RCCB’s) protect?

A

Residual current circuit breakers protect some circuits.

61
Q

What does RCCB stand for?

A

Residual current circuit breakers.

62
Q

What do RCCB’s detect?

A

They detect a difference in the current between the live and neutral wires.

63
Q

Which work faster? RCCB’s or fuses?

A

RCCB’s work much faster than fuses do.

64
Q

What does the earth wire create?

A

The earth wire creates a safe route for the current to flow through if the live wire touches the casting.

65
Q

What would happen if the live wire inside an appliance came loose and touched the metal casting?

A

You would get an electric shock.

66
Q

Why do some appliances not have an earth wire?

A

Because they have plastic castings, or they have been designed so that the live wire cannot touch the casting. As a result, the casting cannot give an electric shock, even if the wires inside become loose.

67
Q

What is the period of an AC supply?

A

The time taken for one complete oscillation.

68
Q

How can you find the period of an AC supply?

A

You can find this by looking at the time between one peak and the next, between one trough and the next, or between any two identical places on adjacent oscillations.

69
Q

What is the frequency of an AC supply?

A

The number of oscillations per second.

70
Q

How can you find the frequency of an AC supply?

A

You can find it from the period: Frequency = 1 ÷ period. Remember to convert to seconds if needed. In this example, 20ms = 20 ÷ 1000 = 0.020s. Frequency = 1 ÷ 0.020 = 50Hz

71
Q

What is a sankey diagram?

A

A diagram using arrows to show the amounts of energy transferred in different forms.

72
Q

What do energy-saving lamps transfer?

A

They transfer a greater proportion of electrical energy as light energy (compared to filament lamps).

73
Q

What is power a measure of?

A

Power is a measure of how quickly energy is transferred.

74
Q

What is the unit of power?

A

The unit of power is the watt, W.

75
Q

You can work out the power of something using this equation:

A

P = E ÷ t
P is the power in watts, W
E is the energy transferred (or work done) in joules, J
t is the time in seconds, s
For example, an electric lamp transfers 500J in 5s. What is its power? Power = 500 ÷ 5 = 100W

76
Q

How can the power of an electrical appliance be calculated?

A

The power of an electrical appliance can be calculated from the current that flows through it and the potential difference across it.

77
Q

Calculating power (again). You can work out power using this equation:

A

P = I x V
P is the power in watts, W
I is the current in amperes (amps), A
V is the potential difference in volts, V
For example, what is the power of a 5A 1.5V lamp?
Power = 5 x 1.5 = 7.5W

78
Q

How can the equation P = I x V be rearranged to find the current if the power and potential difference are known?

A

I = P ÷ V
For example, what current flows through a 1.15 kW electric fire at a potential difference of 230V? Remember that 1.15kW is 1,150W.
Current = 1150 ÷ 230 = 5A
Fuses come in standard ratings of 3A, 5A or 13A. The best fuse to use in this example would be the 13A fuse. The 3A and 5A fuses would blow even when the fire was working normally.

79
Q

You can work out the energy transferred using this equation:

A

E = V x Q
E is the energy transferred in joules, J
V is the potential difference in volts, V
Q is the charge in coulombs, C
For example, much energy is transferred when the potential difference is 120V and the charge is 2C?
Energy transferred = 120 x 2 = 240J

80
Q

What is a kilowatt-hour?

A

A kilowatt-hour is the amount of electrical energy used by a 1kW appliance left on for 1 hour.

81
Q

What do electrical appliances transfer?

A

Electrical appliances transfer electrical energy into other forms e.g sound and heat energy in a radio.

82
Q

What does the amount of energy transferred by an appliance depend on?

A

The amount of energy that is transferred by an appliance depends on its power (how fast the appliance can transfer it) and the amount of time that the appliance is switched on.

83
Q

What are the standard units of electrical energy?

A

The standard units of electrical energy are kilowatt-hours (kWh) not joules (J).

Physics Unit 1 (21 decks)

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