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On the wild side > Light and Waves > Flashcards

Light and Waves Flashcards

1
Q

What are waves?

A

a means of transferring energy

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2
Q

What doesn’t happen with waves?

A

There is no transfer of matter

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3
Q

What are transverse waves?

A

Waves where the direction of energy transfer is perpendicular to the direction of oscillations

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4
Q

What are longitudinal waves?

A

Waves where the direction of energy transfer is along the direction of oscillations

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5
Q

What is an example of a transverse wave?

A

light, waves travelling on the surface of water

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6
Q

What is an example of a longitudinal wave?

A

sound

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7
Q

What is amplitude?

A

the maximum movement of particles from their resting position caused by a wave

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8
Q

What happens when waves strike a concave barrier?

A

They become curved and are made to converge

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9
Q

What happens when waves strike a convex barrier?

A

They are made to diverge and spread out.

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10
Q

What happens when waves enter a shallower region?

A

their wavelength becomes shorter and because the frequency is constant the velocity also decreases

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11
Q

What happens when the waves enter the deeper region?

A

their wavelength increase and so does the velocity

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12
Q

What is necessary for refraction to occur?

A

the boundary between the shallow water and the deep water is at an angle to the direction in which the waves are moving

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13
Q

What happens when waves enter shallow vs deep region?

A

Shallow: bend towards normal and slow down

Deep: bend away form the normal and speed up

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14
Q

What are the common features to all electromagnetic waves?

A

they are all transverse

they all travel at 3x108 m/s

they can all be diffracted, refracted and reflected

they all transfer energy

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15
Q

What is the wave with the longest wavelength?

A

radio

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16
Q

Which wave has the most penetrating power?

A

gamma

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17
Q

Which is the most high frequency wave?

A

gamma

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18
Q

What are radio waves used for?

A

broadcasting and communication

reflect of ionosphere

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19
Q

How are radio waves produced?

A

They are emitted by a transmitter, cross an aerial and the information is receives as they are detected

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20
Q

What detects radio waves?

A

TV aerials and radio

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21
Q

What are the uses of microwaves?

A

cooking, radar and satellite transmissions

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22
Q

How do microwaves heat food?

A

The waves cause water to vibrate more and increase there amplitude. This increase in kinetic energy is essentially an increase in temperature and so the water molecules become very hot.

The food is cooked throughout not just on the outside

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23
Q

What are the dangers of microwaves?

A

They can heat human tissue

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24
Q

How are the dangers of microwaves reduced?

A

Microwaves have metal screens that reflect them and keep them inside the oven.

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25
Q

How are microwaves used for communication?

A

The waves pass through the Earth’s atmosphere and are used to carry signals to orbiting satellites.

They also carry messages sent from phones so therefore can pass through solids (glass/brick)

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26
Q

What do all objects do?

A

emit IR

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27
Q

What makes more IR be emitted?

A

If something is hotter

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28
Q

What detects IR?

A

skin, blackened thermometers, IR cameras

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29
Q

What are the uses of IR?

A

night vision equipment, remote controls for TV, stereo and videos

cooking in grills and toasters

optical fibres

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30
Q

Why are IR used for remotes?

A

They have a low penetrating power and so are unlikely to interact with other signals.

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31
Q

What are the dangers of IR?

A

skin burning and if cells absorb too much they are killed/damaged

32
Q

What emits visible light and detects it?

A

luminous objects

detected by the eye, cameras, LDRs and photographic film

33
Q

What are the uses of Visible light?

A

seeing

light from lasers is used to read compact discs and barcodes

optical fibres: communication and seeing inside the body

34
Q

Which colour has the longest wavelength?

A

red light

35
Q

What is the frequency of red light like?

A

low frequency

36
Q

What are the dangers of UV light?

A

blindness - harmful to eyes

skin cancer - damage to skin

37
Q

How does UV light cause cancer?

A

causes cancer by ionizing cells under skin surface

38
Q

What is UV light used in?

A

UV tanning lamps

some chemicals fluoresce when exposed to UV light

39
Q

What is helping to reduce UV light?

A

ozone absorbs it

40
Q

What does fluorescence mean?

A

an object that absorbs UV light and emits visible light

41
Q

What emits X-rays?

A

X-ray tubes

42
Q

What detects X-rays?

A

photographic film

43
Q

What are X-rays used for?

A

in radiography to observe internal objects of the body

security checks in airports

in the industry to check the internal structures of objects for cracks etc

44
Q

What are the dangers of X-rays?

A

excessive exposure can cause cancer

45
Q

How can you protect against X rays?

A

stand behind a lead screen

protective clothing

46
Q

What are gamma rays emitted by?

A

radioactive material

47
Q

What are gamma rays detected by?

A

Geiger- Muller tube

48
Q

What are the uses of gamma rays?

A

sterilise medical equipment

kill micro-organisms so food keeps for longer

radiotherapy

49
Q

What are the dangers of Gamma?

A

They have a high penetrating power causing mutations in genes that can lead to cancer.

A small dose can cause cells to become cancerous and a large dose can kill cancer cells.

50
Q

What are the benefits of analogue signals?

A

when the signal is amplified so too is the noise which weakens the clarity of the signal

if signals have a similar frequency they interfere with each other and it is difficult to distinguish each signal

Quantisation (when a continuous range is rounded) can give rise to a loss of lots of INFO

wider range of frequencies are needed to broadcast an analogue signal

51
Q

What are the benefits of digital signals?

A

regeneration of signal is clear and exact as noise is ignored easily

Many signals can be transmitted at once with one cable

Quantisation doesn’t lose any information so more info can be transmitter in smaller space without any COMPROMISE on the quality of the signal

More programmes can be broadcast over the same frequencies

Digital systems are easier to design and build

Digital systems deal with easy to process data

Can be handled by microprocessors

Wider bandwidth so the response is clearer yet the noise is lower

Carries more info than analogue because the generator can switch between two values quickly in short space of time compared to analogue where the values are so wide ranging it takes longer to generate

52
Q

Why can digital signals carry more info?

A

They can also squeeze in more programmes, because digital signals can carry more information per second than analogue signals.

When quantisation occurs less info is lost therefore more info is carried. Also they have a large bandwidth.

53
Q

What is an analogue signal?

A

Analogue signals can vary in frequency, amplitude or both continuously.

54
Q

What are digital signals?

A

Digital signals are a series of pulses consisting of just two states, ON (1) or OFF (0). There are no values in between.

55
Q

Explain the meaning of the critical angle

A

When light travels from one medium to another it is refracted; it changes angle due to change in density.
Past a certain angle the light will simply be refracted back into the medium it is in, this angle is the critical angle.

56
Q

What is light?

A

a transverse wave

57
Q

What are the characteristics of images in a plane mirror?

A

image is as far behind as the object is in front

virtual

same size

laterally inverted

58
Q

What is refraction?

A

when a ray of light travels from air into glass or water it slows down as it crosses the boundary between the two media.

This change in speed may cause the ray to change direction; refract.

59
Q

What is the formula for refractive index?

A

n = sin i / sin r

n = speed of light in a vacuum / speed of light in material

60
Q

What happens when the angle of incidence is less than the Ac?

A

A ray of light is refracted as it passes from a more dense medium to less dense one, but a small ray of light is also reflected.

61
Q

What happens when the angle of incidence is equal to the Ac?

A

The light is refracted at 90 degrees to the normal and there is also a small reflected ray

62
Q

What happens when the angle of i is more than the Ac?

A

TOTAL INTERNAL REFLECTION; light reflected back into the denser medium…no refraction occurs

63
Q

What is the formula for the c?

A

sin c = 1/n

64
Q

What can ruin the clear image in a plane mirror?

A

Several faint images form around the main image due to partial internal reflections at the non-silvered glass surface of the mirror

65
Q

How are these extra faint images removed from the mirror?

A

When high quality images are required prisms are used to alter the direction of light rather than mirrors.

66
Q

Where are prisms used?

A

bicycle reflectors and binoculars

67
Q

What is an optical fibre made of?

A

an outer cladding of less optically dense glass and an inner core of optically dense glass

68
Q

How is TIR achieved?

A

The fibres are very narrow so light entering the inner core always strikes the boundary of the two glasses at an angle greater than the Ac.

No light escapes b/c all is Reflected.

69
Q

What are large numbers of OP.FIBRES called?

A

bundle

70
Q

What is done to bundles?

A

tapered to produce a magnified image

71
Q

How does an endoscope work?

A

Light travels down one bundle and illuminates object to be viewed

Light that is reflected by the object travels up a second bundle of fibres

an image of the object is created by the eyepiece

72
Q

How are optical fibres used in modern telecommunications?

A

Electrical signals from telephone converted to light pulses by tiny lasers

The light pulses are sent into the ends of an op.fibres

Light sensitive detector at the other end changes the pulses back to electrical signals

These then flow into the telephone receiver; earpiece

73
Q

What happens when white light passes through a prism?

A

it emerges as a band of colours; spectrum

74
Q

Why is a spectrum formed?

A

White light is a mixture of colours and each colour travels through at a different speed so each colour is refracted by a different angle.

75
Q

What is dispersion?

A

When each different colour of the spectrum emerges from the prism travelling in a different direction b/c each colour is refracted by a differing amount

76
Q

Why does red light disperse the least?

A

The smaller the wavelength of the passing light, the greater is the refractive index observed. Therefore because red has the longest wavelength is deviates the least.

The deviation depends directly on the refractive index. As white light passes through prism, violet, the minimum wavelength, observes maximum refractive index for the prism and since deviation depends directly on the ref index, the violet wavelength gets deviated to the maximum extent.

On the wild side (35 decks)

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