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Physics > Topic 2: Waves and the Electromagnetic Spectrum > Flashcards

Topic 2: Waves and the Electromagnetic Spectrum Flashcards

1
Q

Complete this sentence .

Waves transfer ______ and ______ but do not transfer _______.

A

Waves transfer energy and information

but do not transfer matter.

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2
Q

What are the two types of waves?

A
  1. Transverse

2. Longitudinal

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3
Q

What is a transverse wave?

A

A wave for which the oscillations are
perpendicular to the direction of energy
transfer.

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4
Q

What is a longitudinal wave?

A

A wave for which the oscillations are
parallel to the direction of energy
transfer.

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5
Q

Give two examples of transverse waves.

A
  1. Electromagnetic waves

2. Seismic s-waves

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6
Q

Give two examples of longitudinal

waves.

A
  1. Sound waves

2. Seismic p-waves

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7
Q

What are the two parts of a longitudinal

wave called?

A

Compressions and rarefactions.

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8
Q

What are the two parts of a transverse

wave called?

A

Peaks and troughs.

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9
Q

What is a wave’s amplitude?

A

The maximum displacement of a point

on a wave from its undisturbed position.

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10
Q

What is wavelength?

A

● The distance from a point on a wave to
the same position on the adjacent wave
● Most commonly peak to peak or
trough to trough

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11
Q

What is the frequency of a wave?

A

The number of waves that pass a given point each second.

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12
Q

What is the unit used for frequency?

A

Hertz, Hz

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13
Q

What is meant by a frequency of 200Hz?

A

200 waves pass a given point each second.

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14
Q

What is wave speed?

A

The speed at which energy is transferred through a medium.

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15
Q

What does a wave transfer?

A

Energy.

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16
Q

What is wave velocity?

A

Wave velocity (measured in metres per second) is equal to the product of the wavelength and frequency of the wave.

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17
Q

State the equation used to calculate

wave speed. Give appropriate units.

A

Wave Speed = Frequency x Wavelength

Speed (m/s), Frequency (Hz), Wavelength (m)

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18
Q

What is meant by the period of the wave?

A

The length of time it takes for one full wave to pass through a point.

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19
Q

What word is used to describe when a wave bounces off a surface?

A

Reflection.

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20
Q

What is the normal (in terms of reflection and refraction)?

A

A vertical imaginary line which is

perpendicular to the boundary.

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21
Q

What occurs when light is reflected off a boundary?

A

It bounces off a smooth flat surface so
that the angle of incidence (the angle it
comes in at) is the same as the angle of
reflection (the angle it leaves at).

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22
Q

What is refraction?

A 
Refraction is the change in speed of a
wave as it reaches a boundary between
two media, usually resulting in a change
in direction (if it enters at an angle).
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23
Q

What occurs when light is refracted at a

boundary?

A

● The light changes speed and direction in the new
medium
● If the new medium is more dense, the light will
travel slower and bend towards the normal
● If the new medium is less dense, the light will
travel faster and bend away from the normal

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24
Q

When entering a denser material, light

waves…

A

…slow down and bend towards the

normal.

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25
Q

When entering a less dense material,

light waves…

A

…speed up and bend away from the

normal.

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26
Q

How can refraction be measured?

A

The angle of incidence, i, and angle of
refraction, r, can be measured and
compared. All angles are measured
relative to the normal.

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27
Q

What are the effects of absorption of
different wavelengths of waves in
different mediums?

A

● Some materials behave differently
depending on the wavelength
● An example is glass which will transmit visible light, but reflect UV light

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28
Q

How do sound waves travel through a

solid?

A

The particles in the solid vibrate and
transfer kinetic energy through the
material.

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29
Q

How do sound waves travel through a solid?

A

The particles in the solid vibrate and
transfer kinetic energy through the
material.

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30
Q

How does the human ear work?

A
  1. The outer ear collects the sound which travels into the ear
  2. The sound waves cause the eardrum to vibrate at the same
    frequency
  3. This is amplified by three ossicles (small bones)
  4. This causes the hair in the cochlea to vibrate
  5. The cochlea converts the vibrations into electrical signals
  6. The signals are passed to brain through the auditory nerve
  7. The brain converts the electrical signals into sound
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31
Q

What is the frequency range of human hearing?

A

20 Hz - 20kHz

1kHz = 1000 Hz

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32
Q

What is an ultrasound wave?

A

A sound wave with a frequency greater

than 20,000 Hz.

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33
Q

What is sound of frequencies less than

20Hz called?

A

Infrasound.

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34
Q

What natural event causes seismic
waves to be produced? What types are
produced?

A

● Earthquakes
● They produce both P-waves and
S-waves

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35
Q

Are P waves transverse or longitudinal?

A

Longitudinal

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36
Q

Are S waves transverse or longitudinal?

A

Longitudinal

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37
Q

State a difference between the mediums
that P-waves and S-waves can travel
through.

A

● P-waves travel through both solids and
liquids
● S-waves only travel through solids
(not liquids)

38
Q

What is the significance of P and S waves?

A

They provide evidence that the Earth has
a liquid core; only P waves produced by
an earthquake can be detected on the
other side of the globe.

39
Q

What technique is used to detect objects

in deep water and measure water depth?

A

● Echo sounding
● High frequency sound waves are emitted,
reflected and detected
● Time difference between emission and detection,
alongside wave speed, are used to calculate
distances

40
Q

How does sonar work?

A

● When ultrasound waves are emitted they reflect off boundaries and their echoes are detected.
● The speed of the ultrasound is known and also the time it takes to detect the echoes.
● The equation distance=speed x time is used to find the distance travelled.
● The distance travelled is halved to give the distance between emitter and boundary (as the wave had to travel there and back.

41
Q

How does foetal scanning work?

A

● An ultrasound wave is sent into the patient’s body. It
passes through the body and reflects off the organs and tissue.
● The device then uses the reflected ultrasound waves to produce an image of the foetus.
● Ultrasound is safe and therefore does not damage cells.

42
Q

What is total internal reflection?

A

● When light is completely reflected back
at a boundary between two mediums
● It occurs when light meets a less dense
medium at an angle of incidence larger than the critical angle

43
Q

What is the critical angle?

A

The angle of incidence which causes the

angle of reflection to be 90 degrees.

44
Q

What determines the colour of visible

light waves?

A

The wavelength and frequency of the

light waves.

45
Q

What colour of visible light has the highest frequency?

A

Blue.

46
Q

What colour of visible light has the largest wavelength?

A

Red.

47
Q

What is meant by the term ‘specular reflection’?

A

Rays are reflected from a smooth

surface in a single direction.

48
Q

What is meant by the term ‘diffuse reflection’?

A

Reflection from a rough surface which causes scattering.

49
Q

How does a red colour filter work?

A

● A red filter absorbs all wavelengths of
light other than those in the red range of the spectrum
● This means only red light passes
through the filter

50
Q

What is meant by “opaque?”

A

Not see-through.

51
Q

What governs the colour of an opaque

object?

A

● Different objects reflect different
wavelengths of light by different amounts
● The wavelengths that are most
strongly reflected determine the colour

52
Q

What happens to the wavelengths of
light that aren’t reflected by an opaque
object?

A

Any wavelengths that aren’t reflected are

absorbed by the object.

53
Q

What colour does an object appear if all
wavelengths are reflected by equal
amounts?

A

White.

54
Q

What colour does an object appear if all

wavelengths are absorbed?

A

Black.

55
Q

What types of waves are electromagnetic waves?

A

Transverse

56
Q

What do electromagnetic waves

transfer?

A

Energy (not matter).

57
Q

What type of spectrum do electromagnetic waves form?

A

A continuous spectrum.

58
Q

List the order of the electromagnetic

spectrum in order of increasing wavelength

A

Gamma, X Ray, UV, Visible, Infrared,

Microwaves, Radio

59
Q

What is the highest frequency electromagnetic wave?

A

Gamma waves

60
Q

What is the highest energy electromagnetic wave?

A

Gamma waves

61
Q

What properties are shared by all electromagnetic waves?

A

● They are all transverse waves
● They all travel at the same speed
(3x108 m/s)
● They can travel through a vacuum

62
Q

What range of frequencies of electromagnetic waves can be detected by the human eye?

A

400-700 nanometres

63
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 and in air.

64
Q

What can happen when radiation strikes an object?

A

It can be…

● transmitted
● reflected
● absorbed

65
Q

What do all bodies (objects) emit and absorb?

A

Infrared radiation.

66
Q

What happens to the quantity of infrared
radiation emitted by an object as
temperature increases?

A

The hotter the object, the more infrared radiation it will emit.

67
Q

What happens to the type of radiation
emitted by an object as temperature
increases?

A

The hotter the body the shorter the wavelength

of radiation released (eg. X rays and gamma rays).

68
Q

What is required for a body to be at a

constant temperature?

A

The body would need to emit radiation at the same rate it absorbs it - it needs to radiate at the same average power that it absorbs.

69
Q

Fill the gaps.

________ and __________ distribution of any

emission depends on temperature.

A

Intensity and wavelength distribution of any

emission depends on temperature.

70
Q

What is meant by intensity?

A

The power transferred per unit area; it is

a measure of the energy transferred by a wave.

71
Q

What will happen if the average power
that a object radiates is less than it
absorbs?

A

The temperature of the object will

decrease.

72
Q

What can be said about the rates of
emission and absorption for a body
increasing in temperature?

A

The body is absorbing radiation faster than it is emitting it.

73
Q

Give two factors that affect the

temperature of the Earth.

A
  1. The Earth’s rate of absorption and emission of radiation

2. The amount of reflection of radiation into space

74
Q

How does the Earth’s atmosphere affect

radiation?

A

The atmosphere largely absorbs or reflects radiation from the sun, preventing it from reaching Earth. Some radiation, however, is allowed to pass through and warms the earth.

75
Q

What happens to the radiation emitted from the Earth?

A

It is absorbed and re-emitted in all

directions by greenhouse gases, resulting in the greenhouse effect which warms the earth.

76
Q

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

A

Radio waves.

77
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.

78
Q

Where do gamma rays originate from?

A

They originate from changes in the nuclei of atoms.

79
Q

What health effects can ultraviolet waves

cause?

A

● They can cause the skin to age prematurely

● The can increase the risk of developing skin cancer

80
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

81
Q

What health effects can infrared rays

cause?

A

Infrared waves can cause burns to

skin/tissue.

82
Q

How does electromagnetic radiation affect electron arrangement in atoms?

A

Absorption or emission of electromagnetic radiation can cause electron arrangement to change. (It can remove electrons from the atom or move electrons further from the nucleus)

83
Q

How do atoms become ions?

A

By losing an outer electron.

84
Q

What are the effects of body cells absorbing radiation?

A

Large amounts can damage cells. Smaller amounts cause mutation, causing cells to divide rapidly, which can lead to cancer.

85
Q

State and explain a use of radio waves

A

Communications, because radio waves
are long wavelength and can travel long
distances without losing quality.

86
Q

State and explain a use of microwaves

A

Cooking, as microwaves are absorbed by and heat fat/water in foods.

87
Q

State and explain uses of infrared radiation

A

Cooking food (as it transfers thermal energy) infrared cameras, short range communication.

88
Q

State and explain uses of visible radiation

A

Illuminating (i.e. seeing) and fibre optics, as they reflect best in glass (other waves have wavelengths that are too long/short).

89
Q

State and explain uses of UV radiation

A

Sterilisation, as it kills bacteria, energy
efficient lamps, as it radiates low heat
but high energy, and sun tanning etc.

90
Q

State and explain uses of X rays

A

Medical imaging and treatment, because

they are very high energy and can easily penetrate body tissues.

91
Q

State and explain uses of gamma rays

A

Gamma rays are used in medical treatments, such as radiotherapy in the treatment of cancer.

92
Q

Which waves of the EM spectrum are regarded as most dangerous?

A

Gamma and X rays, as they have the highest energy.

Physics (7 decks)

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