Medical Physics

Question 0

What precautions must be taken when using X-rays?

Answer 0

• Only use if necessary at as low power as possible
• Focused beam so not whole body is exposed
• Technicians should wear lead clothed or stand behind screen
• Technicians should wear detection badges which measure exposure

Question 1

What properties do X-rays have?

Answer 1

High frequency (can cause ionisation)
Short wavelength

Question 2

What was CCD stand for?

Answer 2

Charge coupled device

Question 3

X-rays affect a photographic film, how can this be used?

Answer 3

Form image on X-ray plate

With CCD which allows image to be formed electronically

Question 4

X-rays are absorbed by dense materials, how can this be used?

Answer 4

Take shadow pictures of bone

Detect breaks and fractures

Question 5

X-rays are transmitted by healthy tissue, how can this be used?

Answer 5

In CT scans to detect problems with soft tissues

Question 6

X-rays have high ionising power, how can this be used?

Answer 6

In radiotherapy for killing cancer cells

Question 7

What frequency are ultrasound waves above?

Answer 7

20 000Hz (above human hearing)

Question 8

What happens as ultrasound waves pass from one medium to another?

Answer 8

They are partly reflected at the boundary

Question 9

How do you know how far away a boundary is using ultrasound waves?

Answer 9

The time taken for the reflections is a measure of how far away the boundary is

Question 10

What is the main use of ultrasound waves in medicine?

Answer 10

Prenatal scans

Question 11

Why is using ultrasound waves better than using X-rays for prenatal scans?

Answer 11

Ultrasound waves are non-ionising

Question 12

Other than prenatal scans, what can ultrasound be used for in medicine?

Answer 12

Breaking kidney stones

Question 13

How can ultrasound waves be used to detect flaws or cracks?

Answer 13

Some of the ultrasound waves are reflected back by the flaw or crack. The time taken can then be used to calculate the location

Question 14

Why are ultrasound waves good for cleaning delicate objects?

Answer 14

There is no danger of the object breaking and no need to take object apart

Question 15

Why are X-rays used more than CT scans?

Answer 15

Because CT scans have a long exposure to ionising radiation

Question 16

What is refraction?

Answer 16

Change of direction of light as it passes from one medium to another

Question 17

What does the angle of refraction depend on?

Answer 17

The refractive index of the object

Angle of incidence

Question 18

What are the two sorts of lenses?

Answer 18

Diverging

Converging

Question 19

What is the focal length?

Answer 19

The distance from the lens to the principal focus

Question 20

What is a diverging lens?

Answer 20

A lens that is thinnest at its centre

Question 21

What is another name for a diverging lens?

Answer 21

Concave

Question 22

What sort of lens is thinnest at the centre?

Answer 22

Diverging (concave)

Question 23

A diverging lens produces an image that is…

Answer 23

Virtual

Upright

Question 24

In a diverging lens, the rays are refracted…

Answer 24

Outwards

Question 25

What is a converging lens?

Answer 25

A lens that is thickest at the centre

Question 26

What is another name for a converging lens?

Answer 26

Convex

Question 27

What sort of lens is thickest at the centre?

Answer 27

Converging (convex)

Question 28

Where are the light rays refracted on a double converging lens?

Answer 28

Inwards

Question 29

What is the point where light rays meet?

Answer 29

Focus

Question 30

An image is produced by a converging lens. The distance from the object to the lens is LONGER than the distance from the lens to the focal point. What sort of image is produced?

Answer 30

Real image | Inverted

Question 31

An image is produced by a converging lens. The distance from the object to the lens is SHORTER than the distance from the lens to the focal point. What sort of image is produced?

Answer 31

Virtual image Upright Enlarged On the same side

Question 32

What sort of lens does a camera use?

Answer 32

Converging

Question 33

What sort of lens is in the eye?

Answer 33

Convex

Question 34

Why do people need glasses?

Answer 34

Their lenses are unable to focus the image correctly on the retina

Question 35

What is the function of the retina?

Answer 35

Allows images to focus on it

Question 36

What is the function of the lens?

Answer 36

Focuses the image

Question 37

What is the function of the cornea?

Answer 37

Protects the eye and begins to focus the light

Question 38

What is the function of the pupil?

Answer 38

Allows light to enter the eye

Question 39

What is the function of the iris?

Answer 39

Adjusts to alter the amount of light entering the eye

Question 40

What is the function of the suspensory ligaments?

Answer 40

Connect the lens to the ciliary muscles

Question 41

What is the function of the ciliary muscles?

Answer 41

Contract and relax to alter the shape of the lens (allowing the eye to focus on objects at different distances)

Question 42

A thinner lens allows it to focus on objects that are further/closer?

Answer 42

Further

Question 43

What is wrong with the eye if somebody is short sighted?

Answer 43

Eyeball is too long | Lens is too fat

Question 44

What is wrong with the eye if somebody is long sighted?

Answer 44

Eyeball too short | Lens too thin

Question 45

Where do objects focus on somebody that is short sighted?

Answer 45

In front of the rentina

Question 46

How is short sightedness corrected?

Answer 46

Diverging lens

Question 47

Where do objects focus when somebody is long sighted?

Answer 47

Behind the retina

Question 48

How is long sightedness corrected?

Answer 48

Converging lens

Question 49

What is the power of a lens measured in?

Answer 49

Dioptres (D)

Question 50

What sort of lens would be needed if the dioptres was positive?

Answer 50

Diverging

Question 51

What sort of lens would be needed if the dioptres was positive?

Answer 51

Converging

Question 52

What does the focal length depend on?

Answer 52

* Curvature- more curved lens has higher power and shorter focal length * Refractive index- high refractive index has higher power and shorter focal length

Question 53

People with a higher prescription need more/less curved lenses?

Answer 53

More

Question 54

What is total internal reflection?

Answer 54

When no light is refracted at all

Question 55

When does total internal reflection take place?

Answer 55

When angle of incidence exceeds certain value, called the critical angle

Question 56

What is internal reflection?

Answer 56

When some light is reflected at the interface

Question 57

When the critical angle is greater than the angle of incidence…

Answer 57

Most light is refracted | Some internal reflection

Question 58

When the angle of incidence is equal to the critical angle…

Answer 58

Light is refracted at 90° to the normal | Some internal reflection

Question 59

When the angle of incidence is greater than the critical angle…

Answer 59

Total internal reflection | No refraction

Question 60

How can total internal reflection be used?

Answer 60

To send light along optical fibres to send data for Internet

Question 61

How can total internal reflection be used in medicine?

Answer 61

With an endoscope for internal examinations

Question 62

How can lasers be used in medicine?

Answer 62

Removing verrucas | Reshaping corneas in laser eye surgery