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Physics Unit 3 > P3.1 Medical Applications of Physics > Flashcards

P3.1 Medical Applications of Physics Flashcards

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1
Q

How do X-ray’s affect photographic film?

A

The same way as light (they turn it black)

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2
Q

X-rays are —- by healthy tissue and —- by denser material e.g teeth and bones.

A

1) transmitted

2) absorbed

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3
Q

Name 2 uses of X-rays.

A
  • Diagnoses bone fractures

- Diagnoses dental problems.

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4
Q

What do CCDs do?

A

Form X-rays electronically.

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5
Q

How do CCDs form X-rays electronically?

A

Small silicon chips divided into millions of identical pixels in a grid detect the X-Ray waves and produce electronic signals used to form high resolution images (same technology used camera)

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6
Q

What are CT scans used for?

A

They use X-rays to produce high resolution images of soft and hard tissue.

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7
Q

How do CT scans take place?

A
  • The patient is put inside a cylindrical scanner and an X-Ray beam is fired through the body from an X-day tube and picked up by detectors on the opposite side.
  • X-ray tube and detector are rotated during the scan.
  • Computer interprets scan to form a 3D image from 2D slices.
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8
Q

How are X-rays used to kill cancer cells?

A
  • X-rays focused on rumour using wide beam.
  • Beam is rotated around the patient with the tumour at the centre.
  • This minimises normal cell exposure to radiation.
  • X-rays are at just the right dosage to kill all cancer cells and do minimal damage to normal cells
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9
Q

Name 3 properties that X-rays have.

A
  • Electromagnetic transverse wave.
  • Short wavelength (diameter of an atom)
  • High frequency.
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10
Q

What precautions do radiographers take to stay safe in X-rays?

A
  • Wear lead aprons
  • Stand behind a lead screen
  • Leave room while scans take place
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11
Q

What precautions are taken for a patient having an X-ray to be as safe as possible?

A
  • Lead is used to shield areas of the patients body not being scanned
  • Minimum exposure time
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12
Q

What are ultrasound waves?

A

Higher frequency waves than the range of human hearing (+ 20,000 Hz)

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13
Q

How does ultrasound work?

A
  • When the ultrasound wave passes from one medium to another, some of the waves are reflected off the boundary and some are refracted.
  • The amount of time it takes for the reflections to reach a detector = how far away the boundary is.
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14
Q

Name 2 uses of ultrasound.

A
  • Breaking down of kidney stones

- Pre-natal foetus scanning

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15
Q

Give the one advantage and one disadvantage of ultrasound.

A 
Advantage = non ionising, safe
Disadvantage = images usually fuzzy so it's hard to diagnose illness.
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16
Q

Give the one advantage and two disadvantages of X-rays.

A 
Advantage = clear images of bone and metal
Disadvantage = Ionising, causes cancer, not safe for babies
Disadvantage = doesn't produce images except of bone and metal
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17
Q

Give the two advantages and one disadvantage of CT scans.

A 
Advantage = produces detailed images with high resolution for easy diagnosis. 
Advantage = produces high quality 3D images useful for planning complicated surgery. 
Disadvantage = more x-radiation than standard X-ray photographs so more ionisation.
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18
Q

What is refraction?

A

When waves change direction after entering a new medium.

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19
Q

How does refraction happen?

A
  • When light slows down it bends towards the normal

- When light enters a new medium density changes so light slows down

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20
Q

When does a light wave not refract?

A

If it hits a 90 degree boundary it will slow down but not change direction.

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21
Q

What do convex lenses do?

A
  • Converge light
  • Bulge outwards
  • For longsightedness
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22
Q

What type of image do convex lenses produce between F - 2F?

A
  • Real
  • Inverted
  • Magnified
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23
Q

What type of image do convex lenses produce when the object is closer than F?

A
  • Magnified
  • Virtual
  • Upright
  • Same side of lens
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24
Q

What type of image do concave lens produce?

A
  • Smaller
  • Virtual
  • Same side of lens
  • Upright
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25
Q

What do concave lens do?

A
  • Diverge light
  • Cave inwards
  • Nearsightedness
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26
Q

What is a virtual image?

A

One that cannot be projected on a screen.

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27
Q

How are glasses made thinner?

A
  • The greater the R.I, the flatter the lens will be.

- Powerful lenses can be made thinner using high R.I material

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28
Q

What is the function of the cornea?

A

Protection and initial focus

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29
Q

What is the function of the retina?

A

Where images are formed (covered in light sensitive cells which detect light and send signals to the brain)

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30
Q

What way do waves move when they slow down?

A

They bend towards the normal

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31
Q

What happens if light hits a boundary at 90 degrees?

A

It will not change direction but slow down

32
Q

What happens when light reaches a new medium?

A

Some light will pass through the new medium but some is reflected back, depending on the angle of incidence.

33
Q

What is the ‘refractive index’?

A

The ratio of speed of light in a vacuum to the speed of light in the medium

34
Q

What does the angle of refraction of a ray depend on?

A

The refractive index of the material it travels through

35
Q

What type of lens diverges light?

A

A concave len which caves inwards

36
Q

What type of lens converges light?

A

A convex lens which bulges outwards

37
Q

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

A

A concave lens

38
Q

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

A

A convex lens

39
Q

Define ‘focal length’.

A

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

40
Q

How do lenses produce images?

A

By refracting light and changing its direction

41
Q

What are the three rules of refraction in a converging lens?

A
  • An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
  • An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
  • An incident ray passing through the centre of the lens carries on in the same direction.
42
Q

What are the three rules of refraction in a diverging lens?

A
  • An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
  • An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis.
  • An incident ray passing through the centre of the lens carries on in the same direction.
43
Q

What type of image does an object at 2F form at a convex lens?

A
  • Real
  • Inverted
  • Same size as object
  • At 2F
44
Q

What type of image does an object nearer than F form at a convex lens?

A
  • Virtual
  • Right way up
  • Bigger than the object
  • Same side as the lens
45
Q

What type of image always forms at a concave lens?

A
  • Virtual
  • Right way up
  • Smaller than object
  • Same size as the lens
46
Q

What type of lens does a magnifying glass use?

A

A convex, converging lens

47
Q

Where should the object be placed when using a magnifying glass?

A

Closer than F to produce a virtual, right way up, bigger than object, same side of the lens image

48
Q

What is the relationship between power and the focal length and why?

A

The more powerful a lens, the shorter the focal length as the lens converges rays of light more strongly

49
Q

The power of a converging lens is …

A

positive

50
Q

The power of a diverging lens is …

A

negative

51
Q

What 2 factors does focal length depend on?

A
  • The refractive index of the glass

- The curvature of the lens’ two surfaces

52
Q

How can glasses be made with thinner lenses?

A
  • The greater the refractive index of a glass, the flatter the lens will be
  • This means powerful lenses can be made thinner using glass with a high refractive index
53
Q

What is the purpose of the iris?

A

Controls how much light enters the pupil.

54
Q

What is the purpose of the pupil?

A

Allows light to pass through as it enters the eye.

55
Q

What is the purpose of the lens?

A

Refracts light to focus it onto the retina.

56
Q

What are the purpose of the ciliary muscles?

A

To adjust the shape of the lens to make it more or less curved, so as to increase or decrease the refraction of light.

57
Q

What are the purpose of the suspensory ligaments?

A

To slacken or stretch as the ciliary muscles contract or relax, to adjust the thickness and curvature of the lens.

58
Q

What does the retina correspond to in a camera?

A

CCD

59
Q

What does the lens correspond to in a camera?

A

Lens

60
Q

What does the iris correspond to in a camera?

A

Aperture

61
Q

Define a ‘far point’

A

The furthest distance that the eye can focus on comfortably

62
Q

Define a ‘near point’

A

The closest distance that the eye can focus on comfortably

63
Q

How does the near point depend on age?

A

The older a person is, the further their near point

64
Q

What are the 2 causes of short sightedness?

A
  • Eyeball being too long

- Cornea and lens being too powerful

65
Q

What are the 2 causes of long sightedness?

A
  • Cornea and lens are too weak

- Eyeball too short

66
Q

How can laser surgery be used to correct eye problems?

A
  • It can be used to vaporise some of the cornea to change its shape which changes its focusing ability.
  • This can increase or decrease the power of the cornea so the eye can focus images properly on the retina.
67
Q

How can a lens be used to correct long sightedness?

A
  • A converging lens with positive power can be put in front of the eye.
  • The light is refracted and starts to converge before it enters the eye so the image can be focused on the retina where it belongs.
68
Q

How can a lens be used to correct short sightedness?

A
  • A diverging lens with negative power can be put in front of the eye.
  • The light is refracted and starts to diverge before it enters the eye so the lens can focus it on the retina where it belongs.
69
Q

What is the average near point for adults?

A

25cm

70
Q

What is total internal reflection?

A

The complete reflection of a light ray reaching a less dense medium when the angle of incidence exceeds the critical angle.

71
Q

What is the critical angle?

A

The angle which, if exceeded by the angle of incidence creates total internal refraction.

72
Q

What is the relationship between total internal reflection and the refractive index?

A

The higher the refractive index, the lower the critical angle so the higher the amount of light that is internally refracted.

73
Q

What is an endoscope?

A

A thin tube containing optical fibres that lets surgeons examine inside the body.

74
Q

How do endoscopes use total internal refraction?

A
  • There are two bundles of optical wires
  • One carries light into the body, and the other carries light reflected off internal body surfaces back out.
  • The light waves are bounced off the sides of the inner core of glass or plastic and are reflected repeatedly until they emerge at the other end.
75
Q

Describe one use of endoscopes.

A
  • Keyhole surgery - surgeons only need to cut small holes in people to perform operations

Physics Unit 3 (3 decks)

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