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Physics Michael > P3.1 Medical Applications of Physics Part Two > Flashcards

P3.1 Medical Applications of Physics Part Two Flashcards

From imaging onwards

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1
Q

How is a real image formed?

A

When the light rays from a point on an object come together to form an image - they actually pass through the same point

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2
Q

Where are real images formed? (2)

A

On screens - like the eyes ‘screen’, the retina, and projector screens

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3
Q

How is a virtual image formed?

A

When the light rays from a point on an object are diverging, so the light from the point on the object appears to be coming from somewhere else - they don’t actually pass through this point, they just appear to

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4
Q

Where are virtual images formed? (2)

A

Magnifying glass and mirrors

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5
Q

How do you describe an image? (3)

A

Whether it is magnified or diminished compared to the object, if it is upright or inverted and whether it’s real or virtual

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6
Q

What is a ray diagram?

A

A diagram showing the paths taken by light rays through a lens

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7
Q

What lens do magnifying glasses use?

A

Converging lenses

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8
Q

Where must the object be on a ray diagram for a magnifying glass to work?

A

Closer to the lens than the focal length

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9
Q

What is the magnification formula?

A

Image height / object height

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10
Q

What parts of the eye ‘focuses light rays onto the retina’? (2)

A

The cornea and the lens

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11
Q

What part of the eye ‘contains muscles which alter the size of the pupil’?

A

The iris

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12
Q

What part of the eye is ‘a hole which lets light in’?

A

The pupil

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13
Q

What part of the eye ‘focuses light rays on the retina’?

A

The lens

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14
Q

What part of the eye ‘contracts and relaxes to change the shape of the lens’?

A

The ciliary muscles

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15
Q

What part of the eye ‘holds the lens in place’?

A

The suspensory ligaments

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16
Q

What part of the eye ‘contains light sensitive cells’?

A

The cornea

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17
Q

What part of the eye ‘send impulses to the brain’?

A

The optic nerves

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18
Q

How is the power of the lens and cornea altered?

A

By changing the shape of the lens

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19
Q

How is the lens in the eyes made fatter?

A

When ciliary muscles contract, the tension in the suspensory ligaments is released making the lens take on a fat, more spherical shape

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20
Q

What type of lens does the eye contain?

A

A converging lens

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21
Q

How is the lens in the eye made thinner?

A

When ciliary muscles relax, the ligaments pull on the lens into a thinner, flatter shape

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22
Q

Why is the lens in the eye made fatter?

A

To make it more powerful

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23
Q

Why is the lens in the eye made thinner?

A

To make it less powerful

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24
Q

Which lens shape (in the eye) is more powerful?

A

A fatter lens

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25
Q

What is the far point?

A

The furthest distance that the eye can focus

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26
Q

What is the far point of a human?

A

Infinity

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27
Q

What is the near point?

A

The closest distance that the eye can focus on

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28
Q

What is the near point of a human?

A

For an adult, it is around 25cm

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29
Q

What happens when the eye focuses on closer objects?

A

Its power increases, the lens gets fatter and the focal length decreases

30
Q

How are images formed in a camera?

A

When you take a photo of an object, light from the object travels to the camera is refracted by the lens, forming an image on the film (or the CCD in a digital camera)

31
Q

How do you describe the images formed by a camera? (3)

A

Real, diminished, and inverted - which is the same as they eye

32
Q

How is the lens in a camera similar to the lens and cornea in the eye?

A

They both focus light (either onto a CCD or film in a camera, and a retina in an eye)

33
Q

How is the aperture in a camera similar to the pupil in the eye?

A

They both affect the light entering the eye/camera

34
Q

How is the CCD/film similar to the retina in the eye?

A

They both detect the light focused on it and record it

35
Q

What does short-sightedness prevent people from doing?

A

Focusing on distant objects

36
Q

What is the far point of someone with short-sightedness?

A

Closer to than infinity

37
Q

What is short-sightedness caused by? (2) And why does this cause short-sightedness?

A

It caused by the eyeball being too long, or by the cornea and lens system being too powerful - making the image form before it meets the retina

38
Q

How is short-sightedness corrected?

A

By using a diverging lens

39
Q

What does long-sightedness prevent people from doing?

A

Focusing on near objects

40
Q

What is the near point of someone with long-sightedness?

A

It is further away than normal (25cm or more)

41
Q

What is long-sightedness caused by? (2) And why does this cause long-sightedness?

A

It is caused by the eyeball being too short, or by the cornea and lens system being to weak - making the image form behind the retina

42
Q

How is long-sightedness corrected?

A

By using a converging lens

43
Q

What is the focal length of a lens determined by? (2)

A

The refractive index of the material of the lens, and the curvature of the two surfaces of the lens

44
Q

How does the refractive index determine the focal length of a lens?

A

The greater the refractive index, the shorter the focal length

45
Q

How does the curvature of the two surfaces of a lens determine the focal length of a lens?

A

The greater the curvature, the shorter the focal length

46
Q

How does power affect a lens?

A

The more powerful lens, the more strongly it converges/diverges rays of light

47
Q

What is formula for finding the power of a lens?

A

P = 1/f ==> Power in dioptres (D) = 1 / focal length in meters (m)

48
Q

What power will a converging lens have?

A

A positive power - remember to add the positive sign in front of the value from the formula

49
Q

What power will a diverging lens have?

A

A negative one - the value won’t actually be negative from the formula, you just need to add the minus sign

50
Q

How do you make lenses more powerful?

A

By making its sides more strongly curved

51
Q

What problems are there with more powerful lenses?

A

It makes the lenses thicker, and some people don’t like to wear thick glasses

52
Q

How can powerful lenses be made thinner?

A

The greater the refractive index used to make the lens, the flatter the lens will be

53
Q

What is total internal reflection?

A

When light passes through a boundary between two media, and all of the light is reflected

54
Q

When can total internal reflection occur?

A

When light travels through a dense substance like glass, towards a less dense substance like air

55
Q

What does total internal reflection depend on?

A

The critical angle of the boundary and the angle of incidence of the light

56
Q

What happens when the angle of incidence is less than the critical angle?

A

Most the light refracts out the material, and little bit is internally reflected

57
Q

What happens when the angle of incidence is equal to the critical angle?

A

The emerging (refracted) ray comes out along the boundary, and there is quite a bot of reflection

58
Q

What happens when the angle of incidence is greater than the critical angle?

A

There is total internal reflection

59
Q

What formula links the refractive index with the critical angle?

A

Refractive index = 1 / sin c

c = critical angle in degrees

60
Q

Why cab optical fibres carry visible light long distances?

A

Because of total internal reflection

61
Q

How must optical fibres be made in order for total internal reflection to occur?

A

The inner core must be denser than the outer layer

62
Q

What is an endoscope? What is it used for?

A

A thin tube containing optical fibres that lets health care professionals to examine inside the body

63
Q

What does the first bundle of optical fibres do in an endoscope?

A

The first bundle has light reflecting back and forth so the light emerges inside the patient, lighting up the area of interest

64
Q

What does the second bundle of fibres do in an endoscope?

A

Some light reflects off the inside of the patient from the first bundle into the second bundle - the light reflecting from inside the patient can then be used to form an image through an eyepiece or a TV screen

65
Q

What is the big advantage of using endoscopes?

A

Surgeons can now perform ‘keyhole surgery’ - operations carried out by only cutting tiny holes into people

66
Q

What is an example of a keyhole surgery?

A

Gall bladder surgery, two holes are cut for the keyhole surgery instruments and another is cut for the endoscope

67
Q

What is a laser?

A

A narrow, intense beam of light

68
Q

What can be said about the light waves in lasers?

A

They all have the same wavelengths

69
Q

How are lasers used in surgery?

A

They can be used to cut through body tissue, instead of using a scalpel, and they cauterise the small blood vessels whilst doing this which reduces the amount of blood loss

70
Q

How are lasers used to treat skin conditions?

A

They can be used to treat acne scars, they burn of the top layers of scarred skin revealing the less-scarred layers below

71
Q

What is most common laser surgery? How is this carried out?

A

Laser eye surgery - lasers are used to vaporise some of the cornea to change its shape which changes its focusing ability

72
Q

How does laser eye surgery cure long/short sightedness?

A

By changing the shape of the cornea, the power of the cornea is increased/decreased making the image form on the retina

Physics Michael (14 decks)

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