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Physics > Unit 3A - Medical Applications of Physics > Flashcards

Unit 3A - Medical Applications of Physics Flashcards

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0
Q

What type of frequency and wavelength to x rays have?

A

High frequency, short wavelength

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1
Q

How can X ray images be used in hospitals?

A

For medical diagnosis

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2
Q

How do X-rays work ?

A

They are pass through healthy tissue but are absorbed by denser materials like bones and metals, and so on a photographic film the brighter bits are where fewer x rays get through and so this is the bone

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3
Q

Name two things than x rays can be used to diagnose.

A

Bone fracture or problems with your teeth

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4
Q

What does CT stand for in a CT scan?

A

Computerised axial tomography

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5
Q

What does a CT scan use X-rays for?

A

To produce high resolution images of soft and hard tissue

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6
Q

How can a CT scan detect the difference between soft and hard tissue?

A

Soft tissue can absorb a small amount of X-ray radiation and so it uses this to tell the difference

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7
Q

What happens during a CT scan?

A

An x ray is fired through the body from an x ray tube and picked up by detectors on the opposite side, the X-ray tube and detectors are rotated during the scan and a computer interprets the signals forms images of the tissue.

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8
Q

How can a three dimension image be formed by a CT scan?

A

Multiple two dimensional CT scans can be put together to make a three dimensional image

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9
Q

Why can x rays be used to treat cancer?

A

X rays form ionisation and so high doses will kill living cells and therefore they can be used to kill and treat cancer

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10
Q

Why do x rays have to be carefully focused at the right dosage to kill cancer cells?

A

Minimise the exposure of normal cells to radiation to reduce the chance of damaging the rest of the body

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11
Q

Why do radiographers take precautions to minimise radiation dose?

A

As prolonged exposure to ionising radiation is dangerous to your health

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12
Q

How do radiographers reduce their exposure?

A

Wear lead aprons, stand behind a lead screen or leave the room and keep exposure time at a minimum

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13
Q

What is ultrasound?

A

It is when mechanical vibrations are used to produce sound waves of a higher frequency than the upper limit of human hearing

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14
Q

What is the range of human hearing?

A

20 to 20 000 Hz

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15
Q

Ultrasounds get partially reflected, what is partial reflection?

A

When a wave passes from one medium to another some of the wave is reflected of the boundary and some is transmitted (refracted)

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16
Q

How does ultrasound imaging work?

A

At boundaries between new substances some of the waves get reflected back, and the time taken for the reflections to reach a detector can be used to measure how far away the boundary is.

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17
Q

What speed does ultrasound travel?

A

1500 m/s

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18
Q

What are the two main medical uses of ultrasound?

A

Breaking down kidney stones and pre natal scanning of a foetus

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19
Q

What are kidney stones?

A

Hard masses that can block the urinary track

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20
Q

How can ultrasound help to break down kidney stones?

A

An ultrasound beam concentrates high energy waves at the kidney stone and turn it into sand like particles, which are easily passed out

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21
Q

Why are ultrasounds good to use to break down kidney stones?

A

Patients don’t need surgery and it is relatively painless

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22
Q

How can ultrasound be used in a pre natal scan of a foetus?

A

As ultrasounds pass through the body, they reach boundaries between two media like fluid in the womb and the skin of the foetus this causes some waves to be reflected back and detected. The timings and distribution of these reflections are processed to produce a video image of the foetus.

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23
Q

What’s an advantage of uses ultrasound over X-rays ?

A

They are non ionising and safe, and so are best for use on developing babies

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24
Q

What is the main disadvantage of ultrasound?

A

The images are fuzzy and bad quality which would make if harder to diagnose some conditions and so X-rays or CT scans would be better

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25
Q

What is refraction and what is it caused by?

A

Refraction is when waves change direction as they enter a different medium. This is caused by a change in density from one medium to the other changing the speed of the the waves

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26
Q

What happens to a wave in refraction ?

A

Slows down and bends towards the normal

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27
Q

What is a refractive index?

A

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

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28
Q

What’s the equation to work out the refractive index?

A

Refractive index = sin i / sin r

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29
Q

What are the two types of lense?

A

Converging and diverging

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30
Q

Do converging and diverging lens have the same effects on light rays?

A

No they have opposite effects

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31
Q

What shape is a converging lens and what does it cause light rays to do?

A

Convex, causes parallel rays to converge together at the principal focus

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32
Q

What shape are diverging lens and what does it cause light rays to do ?

A

Concave, they cause parallel rays to diverge

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33
Q

What is the lien passing through the middle of the lens called?

A

The axis

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34
Q

What is the principal focus in converging and diverging lens?

A

Converging - where the rays hitting the lens parallel to the axis meet
Diverging - where the rays hitting the lens parallels to the axis appear to come from

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35
Q

What is the focal length?

A

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

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36
Q

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

A
  1. ) an incident ray parallel to axis refracts through the lens and passes thought the principal focus
  2. ) an incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
  3. ) an incident ray passing through the centre of the lens carries on the same direction
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37
Q

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

A
  1. ) An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
  2. ) an incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
  3. ) am incident ray passing through the centre of the lens carries on in the same direction
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38
Q

What two type of images can lenses produce?

A

Real and virtual

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39
Q

What’s the difference between real and virtual images in lenses?

A

A real image is where light from an object comes together to form an image on a screen, a virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place

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40
Q

What’s an example of a real image?

A

An image formed on an eyes retina

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41
Q

When describing an image through a lense what three things do you need to say?

A

How big it is compared to the object, whether it’s upright or inverted and whether it’s real or virtual

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42
Q

What does an inverted image mean?

A

Upside down

43
Q

How do you draw a ray diagram for an image through a converging lens?

A

Draw a line from the top of the image right through the centre of the lens and continue it on the other side of the lens, draw a line parallel to the top of the object to the lens but then continue the line towards the principal focus. Where the two lines meet is the top of the new object

44
Q

In terms of lenses what does 2F mean?

A

Two times the principal focus

45
Q

What type of image will a converging lens provide a 2F?

A

A real, inverted image the same size as the object

46
Q

What type of image will be produced from a converging lens between F and 2F?

A

It will make a real, inverted images bigger than the object

47
Q

What type of image will a converging lens produce nearer than F?

A

Virtual image the right way up, bigger than the object on the same size as the lens

48
Q

What type of arrows represent a convex and concave lens?

A

Convex - /\

Concave - \/

49
Q

How do you draw a ray diagram for an image through a diverging lens?

A

Draw one line from the top of an object towards the centre of the lens and continue it on the other side of the lens, draw another line going parallel to the axis up to the lens, draw another line this time dotted going from the principal focus in the same size of the image joining up with the lens where the parallel line is. Where the first and last line meet is where the image is

50
Q

What type of image does a diverging lens produce?

A

Always virtual, right way up, smaller than the object and on the same side of the lens as the object

51
Q

What type of lenses do magnifying glasses use?

A

Converging

52
Q

How do magnifying glasses work?

A

By creating a magnified virtual image, the object has to be closer to the lens than the focal length

53
Q

What’s the difference between virtual and real images?

A

You can’t project virtual images onto a screen

54
Q

How do you work out magnification produced by a lens?

A

Image height / object height

55
Q

A coin with the diameter 14mm is places a certain distance behind a magnifying lens, the virtual image produced has a diameter of 36mm, what is the magnification of the lens?

A 
Magnification = image height / object height
Magnification = 35/14
Magnification = 2.5
56
Q

Does a powerful lens have a long focal length?

A

No a short one

57
Q

Why does a powerful lens a short focal length?

A

The more powerful a lens the more strongly it converges rays of light and so the shorter the focal length

58
Q

What formula shows you the power of a lens?

A

Power (D) = 1 / Focal length (m)

59
Q

What is the power of a lens measured in?

A

Dioptres D

60
Q

Between converging and diverging lens which ones has a positive power and which one has a negative power?

A

Converging - positive

Diverging - negative

61
Q

What two factors is the focal length of a lens determined by?

A

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

62
Q

How could you make a glass lens more powerful?

A

Makes the sides more curved

63
Q

Does a powerful lens have a small or high refractive index?

A

High

64
Q

What are the seven main parts of an eye?

A

Suspensory ligaments, retina, ciliary muscle, lens, pupil, cornea and iris

65
Q

What is the cornea and what does it do?

A

Cornea is a transparent window with a convex shape and a high refractive index, does most of the eyes focusing

66
Q

What is the iris and what does it do?

A

The coloured part of the eye, made up of muscles that control the size of the pupil, controlling the light intensity entering the eye

67
Q

What does the lens do?

A

Changes shape to focus light from objects at varying distances

68
Q

How does the lens change shape?

A

It is connected to the suspensory ligaments which are connected to the ciliary muscle. When the ciliary muscle contract, tension is released and the lens turns into a more fat spherical shape. And when they relax the suspensory ligaments pull the lens into a thinner, flatter shape

69
Q

What’s the hole in the middle of the iris called?

A

The pupil

70
Q

What happens at the retina?

A

Images are formed on the retina, it is covered in light sensitive cells which detect the light and send signals to be interpreted

71
Q

The eye can focus on object between which two points?

A

The near and far point

72
Q

What is the far point and how far is it for people?

A

Furthest point that the eye can focus comfortably - infinity

73
Q

What is the near point and how far is it for people?

A

Closest distance that the eye can focus on - 25cm

74
Q

What happens when the eye focuses on closer objects?

A

It’s power increases, the lens changes shape and the focal length decreases

75
Q

A camera forms an image in a similar way to the?

A

Eye

76
Q

How does a camera take a picture?

A

Light from the object travels towards the camera and is refracted by the kens, forming an image on the film

77
Q

What type of image is created by a camera?

A

Real as it is where the light rays actually meet
Smaller than the object
And it is inverted (the camera flips it for you)

78
Q

What in a camera is the equivalent of a retina?

A

The film or CCD

79
Q

Short sight is corrected with what type of lens?

A

Diverging lens

80
Q

What can’t short sighted people focus on?

A

Distant objects

81
Q

What is short sighted caused by?

A

The eyeball being too long, or by the cornea and lens system being too powerful, this means the eye lens can’t produce a focused image on the retina

82
Q

Where does the image focus in a short sighted person?

A

Just before the retina

83
Q

How do diverging lens correct short sight?

A

To diverges light before it enters the eye, so the lens can focus onto the retina

84
Q

Long sighted is corrected with?

A

Converging lenses

85
Q

What can’t long sighted people focus on?

A

Near objects, there near point is further away than normal

86
Q

What causes people to be long sighted?

A

When the cornea and lens are too weak or the eyeball is too short

87
Q

Where does the image focus if you are long sighted?

A

Behind the retina

88
Q

How do converging lens correct long sight?

A

The light is refracted and starts to converge before it enters the eye so that the image is focused in the retina

89
Q

What can be used of surgically correct eye problems?

A

Lasers

90
Q

What is a laser?

A

Narrow, intense beam of light

91
Q

How is a laser used to correct bad vision?

A

A laser can be used to vaporise some of the cornea to change its shaoe, which changes the focusing ability. This can increase or decrease the power of the cornea so that the eye can focus images properly on the retina

92
Q

What is good about the fact lasers can cauterise?

A

It reduces the amount of blood the patient loses and helps to protect against infection

93
Q

Light can be sent along optical fibres using?

A

Total internal radiation

94
Q

How to optical fibres work?

A

Bouncing waves off the sides of the thin inner core of glass or plastic. The wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end

95
Q

What type of substances does total internal reflection have to happen in?

A

The wave has to travel through a dense substance like glass or water towards a less dense substance like air.

96
Q

For total internal reflection the angle of incidence has to be what size compared to the critical angle?

A

It has to be bigger than the critical angle

97
Q

If the angle of incidence is less than the critical angle how much light passes out?

A

Most of the light passes out and only a little bit of it is internally reflected

98
Q

If the angle of incidence is equal to the critical angle how much light passes out?

A

The emerging light comes out along the surface and there is quite a bit of internal reflection

99
Q

If the angle of incidence is greater than the critical angel how much light passes out?

A

No light comes out at all, it’s all internally reflected - total internal reflection

100
Q

A low critical angle is caused by?

A

Dense material with a high refractive index

101
Q

What’s the formula to figure out refractive index?

A

Refractive index = 1 / sin c

C being the critical angle

102
Q

What is an endoscope?

A

Thin tube containing optical fibres that lets surgeon examine inside the body

103
Q

What is each bundle of optical fibres in an endoscope?

A

One carries light to the area of interest and one carries the image back so it can be viewed

104
Q

What’s an advantage of using an endoscope?

A

Surgeons can perform many operations by only cutting teeny holes in people - called key hole surgery

105
Q

What type of waves are x rays and ultrasound?

A

X rays - transverse

Ultrasound - longitudinal

Physics (7 decks)

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