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GCSE Physics > P12 Electromagnetic Waves > Flashcards

P12 Electromagnetic Waves Flashcards

1
Q

What are electromagnetic waves?

A

Transverse waves that transfer energy from the source of the waves to an absorber

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2
Q

What type of spectrum do electromagnetic waves form?

A

A continuous spectrum

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3
Q

How do the speeds of EM radiation differ in a vacuum and in air?

A

Electromagnetic waves all travel at the same speed in a vacuum (space) and in air

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4
Q

How are the waves that from the EM spectrum grouped?

A

In terms of their wavelength and frequency

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5
Q

Order the types of electromagnetic radiation from long to short wavelength/ low to high frequency

A
  • Radio waves
  • Microwaves
  • Infrared
  • Visible Light
  • Ultraviolet
  • X-rays
  • Gamma Rays
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6
Q

What is the wavespeed equation?

A

wave speed = frequency x wavelength = v = f x λ

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7
Q

What are the units of wave speed?

A

m/s

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8
Q

What are the units of frequency?

A

Hz

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9
Q

What are the units of wavelength

A

m

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10
Q

What is white light?

A
  • Light from ordinary lamps and from the sun
  • This is because it has all the colours of the visible spectrum in it
  • The wavelength increases across the spectrum as you go from violet to red
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11
Q

What do our eyes only detect?

A

Visible light and so detect a limited range of EM waves

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12
Q

What may different substances do?

A

Absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength

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13
Q

What types of waves can be produced by oscillations in an electrical circuit?

A

Radio waves.

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14
Q

How can radio waves create an alternating current in a circuit?

A
  • When radio waves are absorbed, they can induce oscillations in a circuit with the same frequency as the waves themselves
  • So radio waves can themselves can themselves induce oscillations in an electrical circuit
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15
Q

What can changes in atoms and the nuclei of atoms result on?

A

Electromagnetic waves being generated or absorbed over a wide frequency range

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16
Q

Where do gamma rays originate from?

A

Changes in the nuclei of atoms.

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17
Q

What health effects can X-rays and Gamma rays cause?

A
  • They are ionising radiation so can cause mutations in genes
  • They can lead to increased risk of developing various cancers
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18
Q

What health effects can ultraviolet waves cause?

A
  • They can cause the skin to age prematurely
  • They can increase the risk of developing skin cancer
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19
Q

What can have hazardous effects on human body tissue and what do they depend on?

A
  • UV waves
  • X-rays
  • Gamma rays
  • Depends on the type of radiation and the size of the dose
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20
Q

Do electromagnetic waves need particles to move?

A

No

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21
Q

What is radiation dose (in sieverts)?

A

A measure of the risk of harm resulting from an exposure of the body to the radiation

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22
Q

What does 1000 millisieverts (mSv) equal?

A

1 siervert (Sv)

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23
Q

Give two practical uses for radio waves

A
  1. Television transmission
  2. Radio transmission
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24
Q

Give two practical uses for microwaves

A
  1. Satellite communications
  2. Cooking food
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25
Q

Give three practical uses for infrared radiation

A
  1. Electrical heaters
  2. Cooking food
  3. Infrared cameras
26
Q

Give one use of visible light

A

Fibre optic communications

27
Q

Give two practical uses for ultraviolet

A
  1. Energy efficient lamps
  2. Sun tanning
28
Q

Give two practical uses for X-rays and gamma rays

A
  1. Medical tanning
  2. Treatments
29
Q

Explain why microwaves are suitable for satellites

A

They can pass through the atmosphere and reach satellites above the Earth

30
Q

Explain why microwaves are suitable for cooking food

A

They can penetrate into food and are absorbed by the water molecules in the food, heating it

31
Q

Explain why infrared radiation is suitable for cooking food

A

Electric cookers that have halogen hobs heat up food faster than ordinary hobs because halogen hobs are designed to emit much more infrared radiation than ordinary hobs

32
Q

What do all electromagnetic waves have in common in space?

A

They all have the same velocity (speed of light)

33
Q

What do electromagnetic waves transfer energy from?

A

A source to absorber

34
Q

What are example of energy transfers from source to absorbers?

A
  • Microwave is the source to food
  • Sun emits energy to Earth
35
Q

What is constant for all EM waves?

A

Speed

36
Q

Is visible light an EM wave?

A

Yes

37
Q

What are some effects due to?

A
  • Differences in velocity
  • When light enters a denser medium, it slows down
  • Shorter wavelengths slow down more than longer wavelengths
  • E.g. Blue light slows down more than red
38
Q

The shorter the wavelength of the waves:

A
  • the more information they can carry
  • the shorter their range (due to increasing absorption by the atmosphere)
  • the less they spread out
39
Q

What is a carrier wave?

A

The waves used to carry any type of signal

40
Q

What are examples of carrier waves?

A
  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
41
Q

What does the type of wave used to carry a signal depend on?

A
  • How much information is in the signal
  • The distance the signal has to travel
42
Q

How is an audio signal transmitted and detected?

A
  • An oscillator supplies carrier waves to the transmitter in the form of an alternating current (a current that repeatedly reverses its direction)
  • The audio signal is supplied to the transmitter where it’s used to modulate the carrier waves
  • The modulated carrier waves from the transmitter are suppplied to the transmitter aerial. The varying alternating current supplied to aerial causes it to emit radio waves that carry the audio signal
  • When the radio waves are absorbed by a receiver aerial, they induce an alternating current in the receiver aerial, which cause oscillations in the receiver. The frequency of the oscillations is the same as the frequency of the radio waves
  • The receiver circuit separates the audio signal from the carrier waves. The audio signal is then supplied to a loudspeaker, which sends out sound waves similar to the sound waves received by the microphone in the radio station
43
Q

Why do x-rays and gamma rays have similar properties?

A
  • are at the short-wavelength end of the electromagnetic spectrum
  • carry much more energy per second than longer wavelength EM waves
44
Q

How do x-rays and gamma rays differ?

A
  • X-rays are produced when electrons or other particles moving at high speeds are stopped - X-ray tubes are used to produce x-rays
  • gamma rays are produced by radioactive substances when unstable nuclei release energy
  • gamma rays have shorter wavelengths than x-rays, so they can penetrate substances more than x-rays can
45
Q

What is ionisation?

A
  • Atoms become charged because they lose electrons
46
Q

What are examples of ionisation?

A

X-rays and gamma rays passsing through substances can knock electrons out of atoms in the substance

47
Q

What are examples of ionising radiation?

A

X-rays and gamma rays

48
Q

How are x-rays used in medicine?

A
  • when the x-ray tube is switched on, X-rays from the tube pass through the part of the patient’s body under investigation
  • X-rays pass through soft-tissue, but they are absorbed by bones, teeth and metal that are not too thin
  • The parts of the film or the detector that the X-rays reach become darker than the other parts
  • So the bones appear lighter than the surrounding tissue, which appears dark
  • The radiograph shows a ‘negative image’ of the bones. A hole or a cavity in a tooth shows up as a dark area in the bright image of the tooth
49
Q

What is contrast medium?

A
  • A substance that an organ that consists of soft tissue can be filled with
  • Absorbs X-rays easily
50
Q

What is a flat-panel detector?

A

A small screen that contains a charge-coupled device (CCD)

51
Q

What is a charge-coupled device (CCD)?

A
  • The sensors in the CCD convert X-rays to light
  • The light rays then create electronjc signals in the sensors that are sent to a computer, which displays a digital X-ray image
52
Q

What is a radiation dose?

A

A measure of the damage done to their body by ionising radiation

53
Q

What does the radiation dose depend on?

A
  • the type of radiation used
  • how long the body is exposed to it
  • the energy per second absorbed by the body from radiation
54
Q

What is x-ray therapy used for?

A

To destroy cancerous tumours in the body

55
Q

How does x-ray therapy work?

A
  • Thick plates between the X-ray tube and the body stop X-rays from reaching healthy body tissues
  • A gap between the plates allows X-rays through to reach the tumour
56
Q

How do x-rays for therapy and imaging differ?

A

X-rays for therapy are shorter in wavelength and carry more energy

57
Q

Why are low-energy X-rays suitable for imaging?

A

Because they are absorbed by bones and teeth but they pass through soft tissue and gaps such as cracks in bones

58
Q

Why can’t low energy x-rays destroy cancerous tumours?

A

They do not carry enough energy

59
Q

What are optical fibres?

A

Very thin glass fibres

60
Q

What is optical fibre used for?

A

Transmitting signals carried by light or infrared radiation

61
Q

How does optical fibre work?

A
  • The light rays can’t escape from the fibre
  • When they reach the surface of the fibre, they are reflected back into the fibre
62
Q

How does optical fibre compare with radiowaves and microwaves?

A
  • Optical fibres carry much more information as light has a much shorter wavelength than radio waves, and so can carry more pulses of waves
  • optical fibres are more secure because the signals stay in the fibre

GCSE Physics (7 decks)

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