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Physics 21st Century > Radiation and Life > Flashcards

Radiation and Life Flashcards

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1
Q

Light is one part of the

A

electromagnetic spectrum?

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2
Q

What is the speed of light in a vacuum?

A

300,000 km/s

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3
Q

What is the relationship between frequency and energy?

A

Higher frequency means more energy

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4
Q

Which are the least energetic electromagnetic waves?

A

Radio waves.

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5
Q

Which are the most energetic electromagnetic waves?

A

Gamma Rays

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6
Q

List the electromagnetic spectrum in order of increasing energy

A

Radio Waves, Microwaves, Infrared, Light, Ultraviolet, X-rays, Gamma rays

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7
Q

What is a “packet” of light called?

A

A photon.

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8
Q

What does the energy of a photon depend on?

A

The frequency of the wave, increasing frequency increases the energy of the photon.

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9
Q

What do solar cells do?

A

Convert electromagnetic radiation from the sun into electricity.

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10
Q

The energy delivered by an electromagnetic wave depends on its…

A

intensity.

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11
Q

Intensity depends on

A

the number of photons per second, and the energy of each photon.

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12
Q

What happens to the area covered by an electromagnetic wave as you move further from the source?

A

The area increases

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13
Q

What happens to the intensity of the electromagnetic radiation as you move further away from the source?

A

It decreases as the area covered increases

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14
Q

How is intensity measured?

A

J/m^2/s

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15
Q

The intensity of a wave in a vacuum varies with distance. What is the mathematical expression?

A

Intensity is inversely proportional to the square of the distance from the source.

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16
Q

What happens to intensity when the wave passes through a medium that absorbs some of the radiation?

A

Intensity drops even faster than the inverse square law predicts.

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17
Q

What is the overall electrical charge of atoms and molecules?

A

Neutral

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18
Q

What is the charge of an electron?

A

-1

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19
Q

What is the charge on an ion?

A

Varies, can be positive or negative

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20
Q

Why is some electromagnetic radiation called ionising radiation?

A

The radiation can knock electrons off atoms and molecules.

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21
Q

Why is only some electromagnetic radiation ionising?

A

Only high energy UV, X-rays and gamma rays have enough energy

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22
Q

What can be started by ionising a molecule?

A

A chemical reaction involving that molecule. (eg colours fade in sunlight)

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23
Q

What electromagnetic radiation comes from radioactive materials?

A

Gamma

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24
Q

How far do gamma rays penetrate the human body?

A

Most go right through

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25
Q

How far do X-rays penetrate the human body?

A

They are absorbed by bone but pass through muscle

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26
Q

What happens to a cell that absorbs gamma or X-ray radiation?

A

They may be damaged by the ions produced. They may therefore be killed, or the damage may eventually lead to cancer.

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27
Q

How can you protect yourself from some ionising radiation?

A

Physical barriers, eg lead and concrete screens

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28
Q

Why do microwaves warm food?

A

The energy from the microwave radiation is absorbed and converted to heat.

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29
Q

Which molecules are good at absorbing microwave radiation?

A

Water

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30
Q

How are people protected from the microwaves in a microwave oven

A

Microwaves reflect off the metal of the walls and door, so cannot escape.

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31
Q

What must food contain to be microwaved?

A

Water… probably a bad idea to try making toast

32
Q

What radiation do mobile phones use?

A

Low intensity microwaves

33
Q

Why are some people worried about using mobile phones?

A

The microwaves will heat up body cells, which could have health implications

34
Q

How is the risk of cancer from mobiles assessed?

A

By comparing cancer rates in large groups of people who do, and do not, use mobile phones.

35
Q

Is there any evidence of harm from mobile phones?

A

No

36
Q

What is the main source of UV radiation on earth?

A

The sun

37
Q

What health risks are associated with UV radiation?

A

Sunburn, skin cancer

38
Q

How do sunscreens and clothing protect people against UV radiation?

A

They absorb the radiation.

39
Q

What is ozone?

A

A molecule that contains 3 atoms of oxygen.

40
Q

Where would you find ozone?

A

Near electrical equipment, and in the upper atmosphere.

41
Q

Why is the ozone layer important?

A

It absorbs UV radiation from the sun

42
Q

What is the effect of the UV radiation on the molecules in the ozone layer?

A

They are changed chemically (as they are ionised).

43
Q

Explain the greenhouse effect?

A

Some of the suns radiation is absorbed by the atmosphere. Some of the radiation is reflected back towards space, then reflected back by clouds. If the earth loses less heat to space than it is absorbing from the sun then it warms up.

44
Q

What is the principal frequency?

A

The radiation emitted with the greatest intensity,

45
Q

What happens to the principal frequency as the temperature of the source rises?

A

It increases.

46
Q

Which has higher frequency, the radiation from the earth or radiation from the sun?

A

The sun.

47
Q

What is the element that enables living things to build such complex molecules?

A

Carbon

48
Q

What is the name given for the way that carbon is reused on earth?

A

Carbon cycle.

49
Q

What removes carbon dioxide from the atmosphere?

A

Plants for photosynthesis, and the oceans.

50
Q

What adds carbon dioxide to the atmosphere?

A

Respiration of living things, decay, use of fossil fuels, volcanoes.

51
Q

What sort of gas is carbon dioxide?

A

Greenhouse gas.

52
Q

How has the level of carbon dioxide varied in the earth’s history?

A

It has been constant for thousands of years.

53
Q

Why has the level of carbon dioxide in the atmosphere remained constant?

A

The rate of production was matched by the rate of absorption.

54
Q

Why has the carbon in the atmosphere gone up over the last 200 years.

A

Burning of fossil fuels means more carbon released; clearing of forests means less carbon being absorbed

55
Q

How is the recent rise in CO2 levels related to the rise in global temperatures?

A

There is a correlation

56
Q

What do many scientists believe is the significance of the correlation between atmospheric CO2 levels and temperature?

A

Many scientists believe that CO2 is the cause of the rise in temperature as CO2 is known to be a greenhouse gas.

57
Q

What is needed for there to be general acceptance that correlation is causation?

A

An explanation of how one could cause the other must be found (a mechanism)

58
Q

What information can be transmitted by electromagnetic waves?

A

Text, voice, music, pictures, data

59
Q

What parts of the electromagnetic spectrum are not absorbed by air?

A

Radio waves and microwaves

60
Q

Which parts of the electromagnetic spectrum do we use for transmitting information on earth?

A

Radio waves and microwaves

61
Q

Why do we use radio waves and microwaves for transmitting information?

A

Other wavelengths are absorbed by atmospheric gases.

62
Q

Which parts of the electromagnetic spectrum are not absorbed by glass, so can be used for transmitting information down optical fibres?

A

Infrared and visible light

63
Q

How is a radio wave used to transmit information?

A

A constant signal (known as the carrier wave) is changed (modulated) in a way that encodes the information.

64
Q

What does a radio receiver do with the radio wave?

A

It demodulates it (subtracts the carrier wave) and translates it into sound.

65
Q

What is a signal that varies continuously with any value called?

A

Analogue.

66
Q

What is a signal that can only have 2 values?

A

Digital

67
Q

How are analogue signals converted to digital?

A

The value of the signal is measured; the value is coded in binary.

68
Q

What is the significance of noise on radio waves?

A

It is impossible to remove the unwanted “noise” from the analogue radio wave.

69
Q

Why is digital transmission better?

A

It is possible to remove most noise, as the signal can only be on or off.

70
Q

What is the unit of digital storage?

A

The byte.

71
Q

What makes up a byte?

A

8 bits.

72
Q

What is a bit?

A

A binary digit, 1 or 0

73
Q

What are the small dots that make up the digital image called?

A

Pixels

74
Q

What does increasing the number of pixels in an image do?

A

It increases the sharpness of the image.

75
Q

How is sound built up from a digital signal?

A

It is generated from a rapid series of values called samples, each sample is a set of binary digits.

76
Q

How does increasing the number of binary digits for a sound affect the quality?

A

It increases it.

77
Q

What is the advantage of coding sound in digital signals?

A

They are easily stored as data on computers.

Physics 21st Century (8 decks)

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