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Poppy > Medical Applications Of Physics > Flashcards

Medical Applications Of Physics Flashcards

1
Q

What are the properties of X-rays

A

They affect a photographic film in the same way as light
They are absorbed by metal and bone
They are transmitted by healthy tissue

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2
Q

What are X-rays used for

A

To form images of bones on photographic film to check for fractures and dental problems

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3
Q

What do X-rays have

A

High frequency and a very short wavelength

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4
Q

What are charged coupled devices used for

A

Forming electronic images of X-rays

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5
Q

What do ct scanners do

A

Use X-rays to produce digital images of a cross section through the body

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6
Q

How cansoft tissue be seen on a X-ray machine

A

Some body organs made of soft tissue such as the intestines can be filled with a contrast medium that absorbs X-rays so they can be seen on n X-ray image

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7
Q

Why can X-rays damage living tissue

A

They are ionising

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8
Q

How can workers protect themselves from X-rays

A

Wear film badges

Use lead screens to shield themselves

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9
Q

What can X-rays be used to treat

A

They can be used to treat cancerous tumours or near the body’s surface

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10
Q

What is the range that a human ear can hear

A

20-20000 hz

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11
Q

What are ultrasound waves

A

Sound waves with a higher frequency than 20000 hz

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12
Q

How can electronic systems produce ultrasound waves

A

When a wave meets a boundary between two different materials part of the wave is reflected. The wave travels back through the material to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary is. The results may be processed by a computer to give an image

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13
Q

In the time between sending out a pulse of ultrasound and it returning to a detector……….

A

It has travelled from the transmitter to a boundary and back, ie twice the distance to the boundary

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14
Q

Why are ultrasound Ray’s safer than X-rays

A

They are non ionising

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15
Q

How are ultrasounds used

A

Scanning unborn babies
Soft tissue such as the eye
Used in therapy eg to shatter kidney stones into small pieces

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16
Q

What is refraction

A

The change in direction of light as it passes from one transparent substance into another

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17
Q

Why does refraction take place

A

Waves change speed when they enter a boundary. The change in speed causes a change in direction

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18
Q

When does refraction not take place when crossing a boundary

A

When the wave travels along the normal

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19
Q

When a light Ray crosses from air into glasss……..

A

It is refracted towards the normal

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20
Q

What is the refracted index

A

Is a measure of how much the substance can refract a light Ray

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21
Q

Where are the angles I and r measured from

A

Between the Ray and the normal

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22
Q

What way will a light Ray refract when it crosses from glass to air

A

Away from the normal

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23
Q

WhAt is seen as a light Ray crosses from glass to air

A

A partially reflected Ray

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24
Q

What happens if the angle of incidence is increased

A

The angle of refraction increases until the refracted Ray emerges along the boundary

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25
Q

What is the angle of incidence also called when it is increased to the point where The angle of refraction increases until the refracted Ray emerges along the boundary

A

Critical angle

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26
Q

What happens if the angle of incidence goes beyond the critical angle

A

The light Ray undergoes total internal reflection

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27
Q

What happens when total internal reflection occurs

A

The angle of reflection is equal to the angle of incidence

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28
Q

What is an endoscope

A

A device used to look inside a patients body without cutting it open or when performing keyhole surgery

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29
Q

What does the endoscope contain and what are they

A

Optical fibres, very thin flexible glass fibres

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30
Q

How is visible light sent along optical fibres

A

By total internal reflection

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31
Q

What may be used as an energy source for endoscopy

A

Laser light

32
Q

What can endoscopy procedures do

A

Cut, cauterise, burn

33
Q

Why is the colour of light matched to the tissue in endoscopy

A

To produce maximum absorption

34
Q

How does endoscopy eye surgery work

A

Using a laser light that passes straight through the cornea at the front of the eye but is absorbed by the retina at the back

35
Q

What happens when parallel Ray’s of light pass through a converging convex lens

A

They are refracted so that they converge to a point

36
Q

What is the principal focus point

A

The point where light rays parallel to the principal axis of a lens are focuses or in the case of a diverging lens, appear to diverge from

37
Q

What is the focal length

A

The distance from the centre of the lens to the principal focus

38
Q

Why is there a principal focus on either side of the lens

A

Because light can pass through the lens in either direction

39
Q

When is a real image formed

A

If the object is further away from the lens than the principal focus

40
Q

What is a real image

A

An image formed where light rays meet

41
Q

What does the size of the real image depend on

A

The position of the object, the nearer the object to the lens the larger the image

42
Q

When is a virtual image formed

A

If the object is further away from the lens than the principal focus

43
Q

What is a virtual image

A

An image seen in a lens of mirror from which light rays appear to come after being refracted by the lens or reflected by the mirror

44
Q

If the object is further away from the lens than the principal focus and a virtual image is created what happens

A

The image is magnified, the lens acts as a magnifying glass

45
Q

How Is magnification calculated

A

Image heigh divided by object height

46
Q

What happens when parallel light rays pass through a diverging concave lens what happens

A

They are refracted so that they diverge away from a point. This point is called the principal focus

47
Q

What is the focal length

A

The distance from the centre of the lens to the principal focus

48
Q

What is the image produced by diverging concave lenses always

A

Virtual

49
Q

What is a Ray diagram

A

A diagram can be drawn to find the position and nature of an image formed by a lens

50
Q

What is the principal axis

A

A straight one that passes along the normal at the centre of each lens surface

51
Q

What are the 3 construction rays from a single point on the object used to locate the corresponding point on the image

A

A Ray parallel to the principal axis is refracted through the principal focus
A Ray through the centre of the lens travels straight on, without refraction
A Ray through the principal focus is refracted parallel to the principal axis

52
Q

Is the image formed in a camera real or virtual?

A

A camera uses a converging lens to form a real image of an object on a film or an array of CCDs

53
Q

What does light enter the eye through

A

Cornea

54
Q

What do the cornea and lens work to do

A

Focus the light on to the retina

55
Q

What does the iris adjust

A

The size of the pupil

56
Q

Why does the iris adjust the size of the pupil

A

To control the amount of light entering the eye

57
Q

What do the ciliary muscles do

A

They alter the thickness of the lens to control the fine focus ing of the eye

58
Q

What are the ciliary muscles attached to the lens with

A

Suspension ligaments

59
Q

What is the retina

A

The light sensitive cells around the inside of the eye

60
Q

What is the blind spot

A

Region where the retina is not sensitive to light (no light sensitive cells present)

61
Q

What does the optic nerve do

A

Carries nerve impulses from the retina to the brain

62
Q

What is the iris

A

Coloured ring of muscle that controls the amount. Of light entering the eye

63
Q

What is the cornea

A

transparent layer that protects the eye and helps to focus light onto the retina

64
Q

What is the pupil

A

The central hole formed by the iris. Light enters the eye through the pupil

65
Q

What is a near point

A

the nearest point to an eye at which an object can be seen in focus by the eye.

66
Q

What is the near point of a normal human eye

A

25cm

67
Q

What is a far point

A

the furthest point from an eye at which an object can be seen in focus by the eye

68
Q

What is the far post. Of a normal human eye

A

Infinity

69
Q

What is the human range of vision

A

25cm to infinity

70
Q

What does it mean to be short sighted

A

A person who can see close objects clearly, but distant objects are blurred because the I corrected image is formed in front of the retina

71
Q

What is short sighted ness caused by

A

The eyeball being too long or the eye lens being too powerful

72
Q

How is short sight corrected

A

Diverging lenses

73
Q

What does it mean to be long sighted

A

They can see distant objects clearly, but close objects are blurred because the I corrected image is formed behind the retina

74
Q

What is long sighted ness caused by

A

The eyeball being too short or the eye lens being too weak

75
Q

How is long sightedness corrected

A

Converging lenses

76
Q

What is the focal length determined by

A

The refractive index of the material from which the lens is made
The curvature of the 2 surfaces of the lens

77
Q

For a lens of a given focal length the greater the refractive index of the lens material,

A

The flatter and thinner the lens can be manufactured

Poppy (12 decks)

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