3- Medical Application Of Physics

Question 1

What are the properties of an X-ray?

Answer 1

Affect a photographic film (the same as light)
Absorbed by metal and bone
Transmit by healthy tissue

Question 2

What are X-rays used for?

Answer 2

Forming images of bones on photographic film (normally to check for fractures and dental problems)

Can also be used for therapy for cancerous tumours near the bodies surface

Question 3

What are 1) Charges Coupled Devices (CCD’s) 2) CT scanners used for?

Answer 3

1) Forming electronic images of X-rays

2) Use X-rays to produce digital images of a cross section through the body

Question 4

How can X-rays be harmful?

Answer 4

Cause ionisation, they can damage living tissue when the pass through it.

Question 5

What frequencies can the human ear detect?

Answer 5

Sound waves with frequencies between 20Hz and 20,000Hz

Question 6

What is ultrasound?

Answer 6

Sound waves with a higher frequency than 20,000Hz (what humans cannot detect)

Question 7

How can electronic systems be used to produce ultrasound?

Answer 7

When a wave meets a boundary between two different materials, part of the wave is reflected and travels back through the material to the detector. The time taken calculates how far the boundary is

Question 8

What is an X-ray?

Answer 8

Part of an electromagnetic spectrum, they have high frequencies and a very short wavelength

Question 9

What can ultrasound be used for and what is the benefit of it?

Answer 9

For scanning, for example unborn babies and the eye.
It can also be used for non medical purposes such as finding cracks in buildings
It cant be used for more sensitive regions or people (pregnant) because it is non-ionising

Question 10

What is refraction?

Answer 10

The change of direction of light as it passes from one transparent substance to another

Question 11

Why does refraction take place?

Answer 11

Waves change speed when they cross a boundary which causes a change in direction (unless it is travelling across the normal)

Question 12

When will a light ray refract towards the normal?

Answer 12

When it crosses from air into glass

Question 13

How is the refractive index measured?

Answer 13

How much the substance can refract a light ray

Question 14

When will a light ray refract away from the normal?

Answer 14

When a light ray crosses from glass to air

Question 15

What is total internal reflection?

Answer 15

When the angle of incidence is increased beyond the critical angle - the angle of reflection is then equal to the angle of incidence

Question 16

What is an endoscope?

Answer 16

Device used to look inside a patients body without cutting them open.
It contains bundles of optical fibres (very thin) which means visible light can be sent along them by total internal refraction

Question 17

What can laser light be used for in terms of endoscopes?

Explain about laser light

Answer 17

As an energy source in the endoscope to carry out some surgical procedures such as cutting or burning.

The colour of it is matched to the type of tissue to produce maximum absorption. An example is eye surgery (through the cornea to the retina)

Question 18

What is the principle focus (focal point) in a converging (convex) lens?

Answer 18

The refracted point of conversion of parallel rays of light through a converging (convex) lens - there is one on either side of the lens because light can pass either way

Question 19

What is the focal length?

Answer 19

The distance from the centre of the lens to the principle focus (focal point).

Question 20

How is a real (inverted) image formed in a converging (convex) lens?

Answer 20

If the object is further away from the lens than the principle focus

Question 21

How does a virtual (upright) image form from a converging (convex) lens or a diverging (concave) lens?

Diverging lens’ always produce a virtual image

Answer 21

If the object is nearer to the lens than the principle focus (formed behind the object).
The image is magnified through the lens

Question 22

What is the principle focus (focal point) of a diverging (concave) lens?

Answer 22

The refracted point of diversion from parallel rays of light through a diverging (concave) lens - there is one on either side of the lens because light can pass either way

Question 23

What does a 1) converging lens 2) diverging lens symbol look like on a diagram?

Answer 23

1) a line with an arrow head on either side

2) a line with a backwards arrow head on either side

Question 24

What is a ray diagram used for?

Answer 24

Finding the image that different lenses produce with objects in different positions

Question 25

What is the principle axis?

Answer 25

He line through the centre of the lens and at right angle to it

Question 26

What are the three construction rays used to locate the objects corresponding point on the image? Ray diagrams

Answer 26

They all start at the point (usually the top) of the object

• parallel to the principle axis then refracted through the principe focus
• through the centre of the lens, travelling straight without refracting
• through the principle focus and refracted parallel to the principe axis

Question 27

What does a camera use and what does it form?

Answer 27

A converging lens to form a real image of an object on a film

Question 28

In the eye, what’s the role of the eye lens?

Answer 28

Focuses light onto the retina

Question 29

In the eye, what’s the role of the retina?

Answer 29

Light sensitive cells around the inside of the eye

Question 30

In the eye, what’s the role of the blind spot?

Answer 30

The region where the retina is not sensitive to light (no light sensitive cells present)

Question 31

In the eye, what’s the role of the optical nerve?

Answer 31

Carries nerve impulses form the retina to the brain

Question 32

In the eye, what’s the role of the ciliary muscles?

Answer 32

Alters the the thickness of the eye lens (attached to it by suspensory ligaments)

Question 33

In the eye, what’s the role of the pupil?

Answer 33

Light enters the eye through it (formed by the iris)

Question 34

In the eye, what’s the role of the cornea?

Answer 34

Transparent layer that protects the eye and helps focus light to the retina

Question 35

In the eye, what’s the role of the iris?

Answer 35

Controls the amount of light entering the eye (coloured ring of muscles)

Question 36

What is the normal human eyes 1) near point 2) far point 3) range of vision?

Answer 36

1) 25cm
2) infinity
3) from 25cm to infinity

Question 37

What, in a digital camera, is equivalent to the 1) pupil 2) retina?

Answer 37

1) Aperture

2) CCD

Question 38

What is short sight caused by and how can it be corrected?

Answer 38

Caused by the eye ball being to long, can be corrected by using diverging lens’

Question 39

What is long sight caused by and how can it be corrected?

Answer 39

Caused by the eyeball being to short, can be corrected by using converging lens’

Question 40

What is the focal length of the lens determined by?

Answer 40

The refractive index of the material of which the lens is made
The curvature of the toe surfaces of the lens