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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 (72 cards)

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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
What is the far point?
The furthest distance that the eye can focus
26
What is the far point of a human?
Infinity
27
What is the near point?
The closest distance that the eye can focus on
28
What is the near point of a human?
For an adult, it is around 25cm
29
What happens when the eye focuses on closer objects?
Its power increases, the lens gets fatter and the focal length decreases
30
How are images formed in a camera?
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
How do you describe the images formed by a camera? (3)
Real, diminished, and inverted - which is the same as they eye
32
How is the lens in a camera similar to the lens and cornea in the eye?
They both focus light (either onto a CCD or film in a camera, and a retina in an eye)
33
How is the aperture in a camera similar to the pupil in the eye?
They both affect the light entering the eye/camera
34
How is the CCD/film similar to the retina in the eye?
They both detect the light focused on it and record it
35
What does short-sightedness prevent people from doing?
Focusing on distant objects
36
What is the far point of someone with short-sightedness?
Closer to than infinity
37
What is short-sightedness caused by? (2) And why does this cause short-sightedness?
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
How is short-sightedness corrected?
By using a diverging lens
39
What does long-sightedness prevent people from doing?
Focusing on near objects
40
What is the near point of someone with long-sightedness?
It is further away than normal (25cm or more)
41
What is long-sightedness caused by? (2) And why does this cause long-sightedness?
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
How is long-sightedness corrected?
By using a converging lens
43
What is the focal length of a lens determined by? (2)
The refractive index of the material of the lens, and the curvature of the two surfaces of the lens
44
How does the refractive index determine the focal length of a lens?
The greater the refractive index, the shorter the focal length
45
How does the curvature of the two surfaces of a lens determine the focal length of a lens?
The greater the curvature, the shorter the focal length
46
How does power affect a lens?
The more powerful lens, the more strongly it converges/diverges rays of light
47
What is formula for finding the power of a lens?
P = 1/f ==> Power in dioptres (D) = 1 / focal length in meters (m)
48
What power will a converging lens have?
A positive power - remember to add the positive sign in front of the value from the formula
49
What power will a diverging lens have?
A negative one - the value won't actually be negative from the formula, you just need to add the minus sign
50
How do you make lenses more powerful?
By making its sides more strongly curved
51
What problems are there with more powerful lenses?
It makes the lenses thicker, and some people don't like to wear thick glasses
52
How can powerful lenses be made thinner?
The greater the refractive index used to make the lens, the flatter the lens will be
53
What is total internal reflection?
When light passes through a boundary between two media, and all of the light is reflected
54
When can total internal reflection occur?
When light travels through a dense substance like glass, towards a less dense substance like air
55
What does total internal reflection depend on?
The critical angle of the boundary and the angle of incidence of the light
56
What happens when the angle of incidence is less than the critical angle?
Most the light refracts out the material, and little bit is internally reflected
57
What happens when the angle of incidence is equal to the critical angle?
The emerging (refracted) ray comes out along the boundary, and there is quite a bot of reflection
58
What happens when the angle of incidence is greater than the critical angle?
There is total internal reflection
59
What formula links the refractive index with the critical angle?
Refractive index = 1 / sin c | c = critical angle in degrees
60
Why cab optical fibres carry visible light long distances?
Because of total internal reflection
61
How must optical fibres be made in order for total internal reflection to occur?
The inner core must be denser than the outer layer
62
What is an endoscope? What is it used for?
A thin tube containing optical fibres that lets health care professionals to examine inside the body
63
What does the first bundle of optical fibres do in an endoscope?
The first bundle has light reflecting back and forth so the light emerges inside the patient, lighting up the area of interest
64
What does the second bundle of fibres do in an endoscope?
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
What is the big advantage of using endoscopes?
Surgeons can now perform 'keyhole surgery' - operations carried out by only cutting tiny holes into people
66
What is an example of a keyhole surgery?
Gall bladder surgery, two holes are cut for the keyhole surgery instruments and another is cut for the endoscope
67
What is a laser?
A narrow, intense beam of light
68
What can be said about the light waves in lasers?
They all have the same wavelengths
69
How are lasers used in surgery?
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
How are lasers used to treat skin conditions?
They can be used to treat acne scars, they burn of the top layers of scarred skin revealing the less-scarred layers below
71
What is most common laser surgery? How is this carried out?
Laser eye surgery - lasers are used to vaporise some of the cornea to change its shape which changes its focusing ability
72
How does laser eye surgery cure long/short sightedness?
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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