# P3.1 Radiation in treatment and medicine Flashcards Preview

## Physics extension edexcel > P3.1 Radiation in treatment and medicine > Flashcards

Flashcards in P3.1 Radiation in treatment and medicine Deck (152)
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1
Q

What does the iris do?

A

Control the amount of light entering the eye

2
Q

What form of radiation does an endoscope use?

A

Visible light

3
Q

What are the two types of ionising rays used to get rid of cancer?

A

Gamma and X-rays

4
Q

What happens to the intensity of radiation as it gets further away from the source?

A

It decreases

5
Q

What happens to the strength of radiation as the density of the medium it passes through increases?

A

It gets weaker

6
Q

How do you find the intensity of radiation?

A

Intensity = power of incident radiation / area

7
Q

What is power measured in?

A

Watts

8
Q

What form of radiation does a PET scanner use?

A

Gamma

9
Q

What type of radiation does a CAT scanner use?

A

X-ray

10
Q

What is intensity?

A

The strength of a wave

11
Q

What is radiation?

A

Energy carried by waves or particles from a source

12
Q

What is a diagnosis?

A

The identification of a medical problem by its signs and symptoms or a medical imaging scan

13
Q

How do endoscopes produce an image?

A

Visible light reflects off features to form an image

14
Q

What is the standard unit of area measured in?

A

Metres squared, m^2

15
Q

What are some types of non-ionising radiation used in medicine?

A

Light, ultrasound

16
Q

Why do doctors place radioactive sources at different distances from a cancer tumour?

A

Because different cancer tumours are treated with different intensities of gamma radiation

17
Q

What factors is intensity influenced by?

A
• distance from the source

- medium that it’s passing through

18
Q

What is incident radiation?

A

The incoming beam of radiation

19
Q

What happens to the intensity of radiation as it travels outwards?

A

It decreases

20
Q

What is intensity measured in?

A

Watts per metre squared, W/m^2

21
Q

What part of the eye causes the size of the pupil to change?

A

The iris

22
Q

What happens to the pupil when the iris gets smaller?

A

It dilates

23
Q

Why can lasers travel long distances?

A

They have a very high intensity

24
Q

What does the pupil change size in response to?

A

Light levels

25
Q

What is the pupil?

A

A round hole in the centre of the iris of the eye

26
Q

What does light enter your eye through?

A

The pupil

27
Q

What do light rays need to pass through to reach the retina?

A

The cornea and lens

28
Q

What is the cornea?

A

The outer transparent layer of the eye

29
Q

What does the cornea do?

A

Refract light entering the eye

30
Q

What does the lens do?

A

Further converge light rays refracted by the cornea to focus them on the retina

31
Q

Where is the retina found?

A

The back of the eye

32
Q

What is the retina?

A

Tissue at the back of the eye that contains light receptors

33
Q

What happens to an image once it reaches the retina?

A

It is converted into electrical impulses by cells in the retina

34
Q

What nerve are electrical impulses formed at the retina carried by?

A

The optic nerve

35
Q

What are ciliary muscles?

A

Muscles that relax or contract to change the shape of the lens of the eye

36
Q

What happens to the pupil when the iris gets bigger?

A

It constricts

37
Q

What does it mean when a pupil constricts?

A

It gets smaller and lets in less light

38
Q

Why do light rays have to converge before they reach the retina?

A

To form a sharp image

39
Q

What happens if too much light enters the eye?

A

It can damage the retina

40
Q

What does it mean when a pupil dilates?

A

It widens and lets in more light

41
Q

What does it mean when light rays converge?

A

They are brought closer together

42
Q

What process happens in the eye in order to converge light rays?

A

Refraction

43
Q

What two parts of the eye cause light rays to refract?

A

The cornea and the lens

44
Q

Why do the ciliary muscles change the shape of the lens when the object being viewed is moved nearer or further away?

A

To keep the image in focus on the retina (depending on distance more or less refraction is needed)

45
Q

What is the far point of an average adult human eye?

A

At infinity

46
Q

What is the near point of the average adult human eye?

A

25cm

47
Q

What is the far point?

A

How far away you can focus on distant objects

48
Q

What is the near point?

A

The closest you can see an un-blurred image

49
Q

What happens to the lens when the ciliary muscles contract?

A

It gets shorter and fatter

50
Q

What happens to the lens when the ciliary muscles relax?

A

It gets longer and thinner

51
Q

What do the ciliary muscles need to do for near objects?

A

Contract

52
Q

What do the ciliary muscles need to do for far objects?

A

Relax

53
Q

Why would someone be short-sighted?

A

The eyeball is too long or the cornea is curved too sharply

54
Q

Why would someone be long-sighted?

A

The eyeball is too short or the lens is not thick or curved enough

55
Q

What does it mean when someone has short sight?

A

Objects a short distance away are clear but far-away objects are blurred

56
Q

What does it mean when someone has long sight?

A

Distant objects are clear but near objects are blurred

57
Q

Why can’t light rays from distant objects focus on the retina in short-sighted people?

A

The light rays refract too quickly in the eye so they are focused before they reach the retina

58
Q

Why can’t light rays from near objects focus on the retina in long-sighted people?

A

The ciliary muscles are taught but the lens can’t bend the light enough so the rays are focused behind the retina

59
Q

What type of lens is used to correct short-sightedness?

A

Diverging

60
Q

What type of lens is used to correct long-sightedness?

A

Converging

61
Q

How does a diverging lens correct short-sightedness?

A

The diverging lens bends the incoming rays apart so that the cornea and lens can focus the rays correctly on the retina themselves

62
Q

How does a converging lens correct long-sightedness?

A

It refracts the rays more to help the cornea and lens finish refracting the rays on the retina

63
Q

What are three treatments for long and short-sightedness?

A
• glasses
• contact lenses
• laser correction
64
Q

What is another name for glasses?

A

Simple lenses

65
Q

What must all contact lenses do?

A

Allow oxygen to permeate the eye

66
Q

Why is it important that contact lenses are cleaned regularly if they aren’t disposable?

A

To prevent infections

67
Q

How does laser correction help correct vision?

A

It uses a finely controlled laser beam to reshape the cornea

68
Q

What is a benefit of using a laser to perform eye surgery?

A

It can make precise incisions in tissue without damaging the surrounding area

69
Q

How does changing the shape of the cornea during laser correction help improve vision?

A

It changes the point at which light rays converge inside the eye

70
Q

What is the focal point?

A

The point at which nearly parallel light rays converge after passing through a lens

71
Q

What is the focal length?

A

The distance from the lens to the focal point

72
Q

What is the object distance?

A

The distance from the object to the lens

73
Q

Where is the image from a converging lens formed?

A

The focal point

74
Q

What happens to parallel rays of light that enter a converging lens?

A

They are refracted and meet at the focal point

75
Q

How is the focal length of a diverging lens measured?

A

The point at which all the rays seem to have come from to the middle of the diverging lens

76
Q

What is the power of a lens measured in?

A

Dioptres

77
Q

What is another name for the focal point?

A

The principal focus

78
Q

What will the faces of a powerful diverging lens look like in comparison to a weaker one?

A

They will be more sharply curved

79
Q

What happens to the focal length of a diverging lens as its power increases?

A

It gets shorter

80
Q

What happens to rays of light passing through a diverging lens when its faces are curved more sharply?

A

They diverge more

81
Q

How is the power of a lens calculated?

A

1 ÷ focal length in metres

82
Q

What power does a lens with a focal length 2 metres have?

A

0.5 dioptres

83
Q

What do you use to find out where an image will form when the light rays from that object aren’t parallel?

A

The lens equation

84
Q

What is the lens equation?

A

1/f = 1/u + 1/v

85
Q

What does f stand for in the lens equation?

A

Focal length

86
Q

What does u stand for in the lens equation?

A

Object distance

87
Q

What does v stand for in the lens equation?

A

Image distance

88
Q

Where are the object distance, image distance and focal length measured from?

A

The lens

89
Q

What are all the distances in the lens equation measured in?

A

Metres

90
Q

What is a real image?

A

An image that can be shown on a screen

91
Q

What is a virtual image?

A

An image that can’t be shown on a screen

92
Q

If the lens equation produces a positive image distance what type of lens was used?

A

Converging

93
Q

Do real images have positive or negative image distances?

A

Positive

94
Q

Do virtual images have positive or negative image distances?

A

Negative

95
Q

Why does the lens equation produce a negative image distance when a diverging lens is used?

A

Because the image isn’t there (virtual image)

96
Q

What does the law of reflection state?

A

Angle of incidence = angle of reflection

97
Q

How can you predict the path of a reflected ray?

A

Using the law of reflection

98
Q

What is reflection?

A

When a wave or particle bounces off a surface

99
Q

Where are the angles of incidence and reflection measured from?

A

From the ray to the normal

100
Q

What is the angle of incidence?

A

The angle between the normal and the particle or wave when it hits a surface

101
Q

What is the angle of reflection?

A

The angle between the normal and the reflected wave as it leaves a surface

102
Q

What is refraction?

A

The change of a wave’s direction of travel when entering a new medium, because a change in density creates a change in speed

103
Q

What happens to a ray when it enters a denser medium?

A

It refracts towards the normal

104
Q

Why does a ray refract towards the normal when it enters a denser medium?

A

Because it slows down

105
Q

Why does a ray refract away from the normal when it enters a less dense medium?

A

Because it speeds up

106
Q

What happens to a ray when it enters a less dense medium than the one it was in?

A

It refracts away from the normal

107
Q

What is Snell’s law used for?

A

To describe the relationship between the angle of incidence and angle of refraction when a wave passes from one medium to another

108
Q

What is another name for Snell’s law?

A

The law of refraction

109
Q

What is Snell’s law?

A

sin(i) / sin(r) = constant

110
Q

What is the constant in Snell’s law equal to?

A

The refractive index of each material
(nr ÷ ni)
(material ray is being refracted in ÷ material ray came from)

111
Q

What does i in Snell’s law stand for?

A

Angle of incidence

112
Q

What does r in Snell’s law stand for?

A

Angle of refraction

113
Q

What is the refractive index of a material?

A

The ratio of the speed of light in a vacuum to the ratio of the speed of light in that material

114
Q

What does the direction a ray takes when it reaches the boundary of a different medium depend on?

A
• the angle of the ray

- the speed at which the ray can travel in both media

115
Q

What is the critical angle?

A

The smallest angle of incidence at which the angle of refraction is 90 degrees or total internal reflection occurs

116
Q

What will happen when a ray enters a medium at less than the critical angle?

A

Part of the wave is refracted and part is reflected

117
Q

What will happen when a ray enters a medium at an angle greater than the critical angle?

A

Total internal reflection

118
Q

What will happen when a ray enters a medium at the critical angle?

A

It will refract at 90 degrees (travels along the boundary)

119
Q

What is total internal reflection?

A

When all of a wave is reflected back from a boundary instead of being refracted, nothing passes through

120
Q

What is the critical angle for most types of glass?

A

42 degrees

121
Q

Why are diamonds cut to make them sparkle?

A

To increase the amount of total internal reflection

122
Q

Why do diamonds sparkle so much?

A

Their critical angle is very low so a lot of light gets trapped and bounces around inside

123
Q

How are diamonds cut so that they sparkle as much as possible?

A

At angles that increase total internal reflection

124
Q

What does the size of the critical angle depend on?

A

How fast the rays can travel through the two media

125
Q

What happens to the angle of incidence and refraction when a wave enters a medium where it speeds up?

A

It decreases

126
Q

What happens to the amount of refraction and reflection as the angle of incidence decreases?

A

There is more refraction and less reflection

127
Q

What happens to the rays of the infrared source in a car rain sensor when it doesn’t rain?

A

Total internal reflection

128
Q

How does the infrared detector in a car rain sensor see if it’s raining?

A

If it has been raining it detects less infrared from the source because it has been refracted

129
Q

Why is the infrared ray in a car rain sensor refracted when it rains but totally reflected when it doesn’t?

A

The infrared source is positioned at an angle greater than the critical angle from glass to air so total internal reflection occurs. When it rains this angle is no longer greater than the critical angle (change to glass to water) so the ray refracts

130
Q

What law can be applied to calculate a critical angle?

A

Snell’s law when sin(i) is replaced with sin(c)

131
Q

What is the angle of refraction when a ray is travelling along the critical angle?

A

90 degrees

132
Q

What is sin(90) equal to?

A

1

133
Q

What is the refractive index of air?

A

1

134
Q

What is the formula for finding a critical angle?

A

Sin(c)/sin(r) = nr/ni

135
Q

When a refractive index increases, what happens to the critical angle?

A

It gets smaller

136
Q

What is an optical fibre?

A

A glass fibre that transmits light from one end to the other by total internal reflection

137
Q

What type of rays are used to transmit signals in optical fibres for telephones, TVs and other data communications?

A

Infrared and visible light

138
Q

What are optical fibres in an endoscope used for?

A
• bringing light to the end of the endoscope

- bringing reflected light from the object back to the viewer so that they can see the image

139
Q

What focuses the gathered light reflected off the inside of the body in an endoscope?

A

The eyepiece lens

140
Q

What are optical fibres made of?

A

High transparency glass

141
Q

In what form is information transferred down in bundles of optical fibres?

A

Pulses of light

142
Q

Why are fibre optic cables faster than traditional copper cable telephone lines?

A

They can carry more signals

143
Q

How is refractive index calculated?

A

1/sin(c)

144
Q

What are the uses of lasers?

A
• laser eye surgery
• cutting through materials
• engraving
• cauterisation
145
Q

What does it mean when a laser has low divergence?

A

It spreads out very little

146
Q

What happens when an ultrasound wave enters a different medium than the one it was in?

A

It is partially reflected

147
Q

Can ultrasound waves travel through solid objects?

A

Yes

148
Q

What does the device in a medical ultrasound scanner do?

A

It both transmits and receives the ultrasound waves

149
Q

How does an ultrasound scan produce an image of the inside of the body?

A
• the device emits ultrasound waves
• these go through the body and are reflected at the interfaces between different tissues
• the device detects the reflected waves
• these are converted to an image onscreen
150
Q

What is a medical example of the use of ultrasound in both diagnosis and treatment?

A

The location of kidney stones and the use of high intensity ultrasound waves to break them up

151
Q

What are the uses of the absorption of ultrasound energy in treatment?

A
• breaking up kidney stones
• treating injured muscles
• treating swollen tissues
152
Q

How is ultrasound energy directed effectively?

A
• by focusing it

- by controlling its intensity