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Physics > Electricity and waves > Flashcards

Electricity and waves Flashcards

1
Q

Define current

A

The flow of electrons round a circuit

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2
Q

Define voltage

A

The driving force that pushes the circuit around

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3
Q

Define resistance

A

Anything that slows the flow down

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4
Q

Which way do electrons flow?

A

Opposite the conventional current

- to +

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5
Q

What colours are the wires in a three pin plug?

A

Brown- live
Green/yellow- earth
Blue- neutral

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6
Q

What does a fuse do in a three pin plug?

A

When the current exceeds the fuse’s max current, it will melt, leading to a break in the circuit so the plug can’t set on fire

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7
Q

What does the earth wire do?

A

If the heating element wire breaks and touches the metal case, current will flow to earth as it offers the least resistance

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8
Q

What is direct current (D.C)

A

Current that only flows in one direction (+ to -)

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9
Q

What is alternating current? (A.C)

A

Current flows one way, then back- constantly changing direction

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10
Q

What is frequency?

A

The number of waves/cycles in a second

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11
Q

What is the formula for power, current and resistance?

A

P = i*2 x R

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12
Q

What is the formula for energy transferred, power and time?

A

E = P x t

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13
Q

Why are some earth pins plastic on three pin plugs?

A

For double insulation, so that there’s no chance of touching live or neutral wires due to everything encased in plastic

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14
Q

Name three safety features in a three pin plug

A

Fuse, as it melts and breaks the circuit if the current is too high

Earth wire, as it directs the current into the earth if a wire breaks and connects with the metal covering

Cable grip, as it keeps all the wires in place, so there’s no chance you could accidentally touch one or it could move out of its socket

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15
Q

Why is an RCB different to a fuse?

A

A Residual Circuit Breaker is different as a fuse will only melt if the current exceeds the fuse rating. The RCB will detect a difference in the Live and Neutral wires and flip a switch, breaking the circuit as a difference in the two wires would make the current be able to flow through the user, to the earth

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16
Q

If a current is at 4A, what fuse should be used?

A

The next fuse available after 4A, but NOT 4A

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17
Q

What should the difference in voltage be between the Live and Neutral wire for it to be safe?

A

0 volts, they should be the same voltage

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18
Q

What is the voltage of mains electricity?

A

230 volts

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19
Q

What is the frequency of mains electricity?

A

50 Hertz

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20
Q

What does the ammeter measure?

A

Current in Amps

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21
Q

What does the voltmeter measure?

A

Voltage in Volts

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22
Q

How is the ammeter connected to a circuit?

A

In series

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23
Q

How is a voltmeter connected to a circuit?

A

In parallel

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24
Q

What does a resistor look like on a current/voltage graph?

A

A straight line

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25
Q

What does a filament lamp look like on a current/voltage graph and why?

A

A curve, as the hotter the bulb gets, the more resistance it has

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26
Q

What is an LDR?

A

A light dependent resistor (the resistance is highest in darkness)

This is used for automatic lights (when it gets dark, the light comes on)

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27
Q

What does a thermistor do?

A

They have a high resistance in cold conditions and the resistance falls as it gets hotter

This can be used for central heating thermostats

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28
Q

What is electromagnetic induction?

A

The creation of a voltage in a wire which is experiencing a change in magnetic field

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29
Q

What is the ‘dynamo effect’?

A

Using electromagnetic induction to transform kinetic energy into electrical energy

E.g a turbine

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30
Q

What two situations can you get an electromagnetic induction?

A

An electrical conductor moves through the magnetic field

The magnetic field through an electrical conductor changes

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31
Q

Why do generators produce an alternating current?

A

Because as a coil rotates in a magnetic field, every half a turn the current swaps direction as it is constantly switching between the north and south end

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32
Q

If the generator is going at 50Hz, how many times does it rotate a second?

A

50 times a second

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33
Q

What is the national grid?

A

A network that covers the whole country and takes electricity from power stations to homes and industries

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34
Q

How does a power station generate electricity?

A

Fuel is burned, creating steam that turns the turbine

The steam is condensed and passed back into the boiler as the turbine is connected to the generator

The turbine spins so the generator spins, creating electricity

35
Q

What are transformers used for in the national grid?

A

Providing more electricity requires a higher voltage or current
Current will burn the wires so voltage is used to generate more electricity

The voltage is transformed to 400,000V by a step up transformer
The electricity goes through the pylons which are well insulated
It is then transformed by a step down transformer to 230V

36
Q

Define ‘electrical power’

A

The rate of transfer of electrical energy

37
Q

What is a kilowatt-hour?

A

The amount of electrical energy converted by a 1kW left on for an hour

38
Q

What is ‘amplitude’ in a wave?

A

The displacement (gap) from the rest to the crest

39
Q

What is the wavelength in a wave?

A

The length of one wave (crest to crest)

40
Q

What is frequency in a wave?

A

The number of complete waves passing a certain point per second

Measured in hertz

41
Q

What are transverse waves?

A

The vibrations are at 90 degrees to the direction of travel

Example : light, other EM waves

42
Q

What are longitudinal waves?

A

The vibrations are along the same direction as the wave is travelling

Examples: sound, shock waves

43
Q

What are compressions and rarefactions in longitudinal waves?

A

Compressions is when the vibrations are concentrated, compressing a point along the wave

Rarefactions are when the wave is stretched and there vibrations are less concentrated

44
Q

What is the order of EM waves?

A 
Racist
Muppets
Insult
Very
Ugly
Xenophobic
Geese
Radio waves
Microwaves
Infra-red
Visible light
Ultraviolet
X-ray
Gamma
45
Q

What is the order of wave length in colours?

A 
Red
Orange
Yellow
Green
Blue
Indigo
Violet
46
Q

How are gamma rays formed?

A

They are formed by the decay of a father nucleus

47
Q

How are x-rays formed?

A

Fast moving electrons that hit a metal surface

48
Q

How do radio waves transfer through an Ariel

A

There is an alternating radio wave when it hits, the alternating wave goes to the speaker

49
Q

What happens to different EM waves in a vacuum?

A

They all have the same speed

50
Q

Do longer wavelengths or shorter wavelengths have the most energy?

A

Shorter

51
Q

What is interference?

A

When two or more waves of a similar frequency come into contact and combine, creating a combined amplitude

52
Q

What happens when a wave is reflected?

A

The waves rebound off of the material

53
Q

What happens when a wave is refracted?

A

They go through a material and change direction

54
Q

What happens when a wave is diffracted?

A

The wave bends round an obstacle, causing the waves to spread out

55
Q

How does diffraction work?

A

Waves spread out at the edges when they pass through a gap or past an object
This depends on the size of the gap relative to the wavelength

56
Q

What 5 things can an object do to a wave?

A 
Diffract it
Absorb it
Transmit it
Reflect it
Refract it
57
Q

What happens if a wave goes into a material that’s denser?

A

It goes slower (except for sound waves that travel faster)

58
Q

What happens if a wave hits a dense material head on?

A

It carries in the same direction but slower

59
Q

What happens if a wave hits a denser material at an angle?

A

It gets refracted

The side that hits first slows down whilst the other side continues at the same pace

This makes the wave turn until both sides are in the material

60
Q

In refraction, what are the rays called?

A

Incident ray - the one entering the material
Refracted ray - ray refracted through the material
emergent ray - ray coming out of the material

61
Q

In refraction, what is the normal?

A

90 degrees to the material

62
Q

In refraction, what happens if the angle of incidence is less than the critical angle?

A

Most of the light passes out but some is internally reflected

63
Q

In refraction, what happens when the angle of incident is equal to the critical angle?

A

The emerging Ray comes out along the surface of the material and there’s quite a bit of internal reflection

64
Q

In refraction, what happens when the angle of incident is bigger than the critical angle?

A

No light comes out, it’s all internally reflected

65
Q

How do optical fibres work?

A

They bounce visible or infrared light waves off the sides of a thin inner core of glass or plastic using total internal reflection
The wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end

66
Q

Why can optical wires not be bent sharply?

A

They use total internal reflection to bounce light rays across the wire

If it’s bent, the angle of incidence might fall below the critical angle

67
Q

Why are higher frequency waves more dangerous?

A

The energy of EM waves is proportional to its frequency

So higher frequency waves have more energy and energy does damage

68
Q

Give examples of potential health risks with waves?

A 
Infrared could burn you
Visible light could blind you
UV light causes cancer
Microwave could potentially be absorbed by water molecules in cells
Gamma rays can destroy cells
69
Q

How does UV light give you cancer?

A

They damage the dna in your cells

Dark skin protects against UV rays as it absorbs them before they get to sensitive cells

70
Q

How do radio waves get around the earth?

A

Long radio waves could diffract, bend around the earth - different countries

Short radio waves could break through the ionosphere, reach a satellite and be redirected back down - cell phone

Long radio waves can’t break through the ionosphere so is instead bounced off it - tv and radio

71
Q

What is the ionosphere?

A

An electrically charged later in the earth’s upper atmosphere

72
Q

How do microwave ovens work?

A

Microwaves are go in a few cm and are absorbed by the water molecules, the energy is then connected to other parts

73
Q

How do X-rays work?

A

X rays pass through flesh but can’t pass through denser materials like bone
So the graph shows the places the x rays aren’t absorbed

74
Q

How does infrared vision work?

A

It measures the IR radiation coming off of something (heat)

75
Q

How does an ultrasound scan work?

A

Ultrasound is made up of high frequency sound waves

As these hit a surface, some are partially reflected, this creates an image on the computer

76
Q

How does iris scanning work?

A

Each iris has a unique pattern

Light is reflected off your iris to make a picture, this shows whether it’s your identity or not

77
Q

How does a CD work?

A

The surface has shallow bits and high bits

A laser is reflected into it and the two bits shine differently, this difference is picked up and converted into an electrical signal

78
Q

What is the difference between analogue signals and digital signals?

A

Analogue takes any value in a certain range

Digital is either on or off

79
Q

Why do signals need to be amplified?

A

They get weaker the further they go and also pick up interference

80
Q

Why is noise less of an issue with digital signals?

A

Digital signals are much higher quality

Digital signals are also easier to work with computers

81
Q

What are seismic waves caused by?

A

Earthquakes

82
Q

What are the two different seismic waves?

A

P-waves - longitudinal and travels through solids and liquids (is faster than S-waves)

S-waves - transverse and only travels through solids (slower than P-waves)

83
Q

How do S-waves tell us the outer core of the earth is liquid?

A

They get through the mantle because it’s solid but can’t get through the outer core so it must be liquid

(They can only go through solids)

84
Q

How do P-waves show is that the inner core is solid?

A

They travel slightly faster through the inner core

Physics (11 decks)

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