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P3 > Medical Physics > Flashcards

Medical Physics Flashcards

0
Q

What precautions must be taken when using X-rays?

A
  • Only use if necessary at as low power as possible
  • Focused beam so not whole body is exposed
  • Technicians should wear lead clothed or stand behind screen
  • Technicians should wear detection badges which measure exposure
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1
Q

What properties do X-rays have?

A 
High frequency (can cause ionisation)
Short wavelength
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2
Q

What was CCD stand for?

A

Charge coupled device

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3
Q

X-rays affect a photographic film, how can this be used?

A

Form image on X-ray plate

With CCD which allows image to be formed electronically

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4
Q

X-rays are absorbed by dense materials, how can this be used?

A

Take shadow pictures of bone

Detect breaks and fractures

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5
Q

X-rays are transmitted by healthy tissue, how can this be used?

A

In CT scans to detect problems with soft tissues

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6
Q

X-rays have high ionising power, how can this be used?

A

In radiotherapy for killing cancer cells

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7
Q

What frequency are ultrasound waves above?

A

20 000Hz (above human hearing)

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8
Q

What happens as ultrasound waves pass from one medium to another?

A

They are partly reflected at the boundary

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9
Q

How do you know how far away a boundary is using ultrasound waves?

A

The time taken for the reflections is a measure of how far away the boundary is

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10
Q

What is the main use of ultrasound waves in medicine?

A

Prenatal scans

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11
Q

Why is using ultrasound waves better than using X-rays for prenatal scans?

A

Ultrasound waves are non-ionising

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12
Q

Other than prenatal scans, what can ultrasound be used for in medicine?

A

Breaking kidney stones

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13
Q

How can ultrasound waves be used to detect flaws or cracks?

A

Some of the ultrasound waves are reflected back by the flaw or crack. The time taken can then be used to calculate the location

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14
Q

Why are ultrasound waves good for cleaning delicate objects?

A

There is no danger of the object breaking and no need to take object apart

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15
Q

Why are X-rays used more than CT scans?

A

Because CT scans have a long exposure to ionising radiation

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16
Q

What is refraction?

A

Change of direction of light as it passes from one medium to another

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17
Q

What does the angle of refraction depend on?

A

The refractive index of the object

Angle of incidence

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18
Q

What are the two sorts of lenses?

A

Diverging

Converging

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19
Q

What is the focal length?

A

The distance from the lens to the principal focus

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20
Q

What is a diverging lens?

A

A lens that is thinnest at its centre

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21
Q

What is another name for a diverging lens?

A

Concave

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22
Q

What sort of lens is thinnest at the centre?

A

Diverging (concave)

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23
Q

A diverging lens produces an image that is…

A

Virtual

Upright

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24
Q

In a diverging lens, the rays are refracted…

A

Outwards

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25
Q

What is a converging lens?

A

A lens that is thickest at the centre

26
Q

What is another name for a converging lens?

A

Convex

27
Q

What sort of lens is thickest at the centre?

A

Converging (convex)

28
Q

Where are the light rays refracted on a double converging lens?

A

Inwards

29
Q

What is the point where light rays meet?

A

Focus

30
Q

An image is produced by a converging lens. The distance from the object to the lens is LONGER than the distance from the lens to the focal point. What sort of image is produced?

A

Real image

Inverted

31
Q

An image is produced by a converging lens. The distance from the object to the lens is SHORTER than the distance from the lens to the focal point. What sort of image is produced?

A

Virtual image
Upright
Enlarged
On the same side

32
Q

What sort of lens does a camera use?

A

Converging

33
Q

What sort of lens is in the eye?

A

Convex

34
Q

Why do people need glasses?

A

Their lenses are unable to focus the image correctly on the retina

35
Q

What is the function of the retina?

A

Allows images to focus on it

36
Q

What is the function of the lens?

A

Focuses the image

37
Q

What is the function of the cornea?

A

Protects the eye and begins to focus the light

38
Q

What is the function of the pupil?

A

Allows light to enter the eye

39
Q

What is the function of the iris?

A

Adjusts to alter the amount of light entering the eye

40
Q

What is the function of the suspensory ligaments?

A

Connect the lens to the ciliary muscles

41
Q

What is the function of the ciliary muscles?

A

Contract and relax to alter the shape of the lens (allowing the eye to focus on objects at different distances)

42
Q

A thinner lens allows it to focus on objects that are further/closer?

A

Further

43
Q

What is wrong with the eye if somebody is short sighted?

A

Eyeball is too long

Lens is too fat

44
Q

What is wrong with the eye if somebody is long sighted?

A

Eyeball too short

Lens too thin

45
Q

Where do objects focus on somebody that is short sighted?

A

In front of the rentina

46
Q

How is short sightedness corrected?

A

Diverging lens

47
Q

Where do objects focus when somebody is long sighted?

A

Behind the retina

48
Q

How is long sightedness corrected?

A

Converging lens

49
Q

What is the power of a lens measured in?

A

Dioptres (D)

50
Q

What sort of lens would be needed if the dioptres was positive?

A

Diverging

51
Q

What sort of lens would be needed if the dioptres was positive?

A

Converging

52
Q

What does the focal length depend on?

A
  • Curvature- more curved lens has higher power and shorter focal length
  • Refractive index- high refractive index has higher power and shorter focal length
53
Q

People with a higher prescription need more/less curved lenses?

A

More

54
Q

What is total internal reflection?

A

When no light is refracted at all

55
Q

When does total internal reflection take place?

A

When angle of incidence exceeds certain value, called the critical angle

56
Q

What is internal reflection?

A

When some light is reflected at the interface

57
Q

When the critical angle is greater than the angle of incidence…

A

Most light is refracted

Some internal reflection

58
Q

When the angle of incidence is equal to the critical angle…

A

Light is refracted at 90° to the normal

Some internal reflection

59
Q

When the angle of incidence is greater than the critical angle…

A

Total internal reflection

No refraction

60
Q

How can total internal reflection be used?

A

To send light along optical fibres to send data for Internet

61
Q

How can total internal reflection be used in medicine?

A

With an endoscope for internal examinations

62
Q

How can lasers be used in medicine?

A

Removing verrucas

Reshaping corneas in laser eye surgery

P3 (3 decks)

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