Medical Physics

Question 1

why do doctors carry X-ray counters

Answer 1

X-rays are ionising and can kill healthy cells/cause damage to DNA/damage cells/ cause cancer

Question 2

4 examples of medicinal uses of X-rays

Answer 2

• imaging bones
• imaging dental problems
• imaging the body
• killing cancer cells

Question 3

describe ultrasound

Answer 3

a longitudinal wave above 20,000Hz which is way beyond our upper range of human hearing

Question 4

how are images formed using ultrasound

Answer 4

waves are partially reflected when they meet a boundary between two substances. the time taken for the echo gives the distance of the boundary. reflected waves are collected and processed into an image by a computer

Question 5

what is refraction

Answer 5

the bending of light moving from one substance(medium) to another

Question 6

what is the name of the point which a convex lens makes light rays meet

Answer 6

the focal point

Question 7

why is an image formed from a lens virtual

Answer 7

the real light rays do not meet to make the image, virtual light rays meet instead

Question 8

why are some people short sighted

Answer 8

their eyeball is too long or the lens is unable to focus light rays on the retina

Question 9

why are some people long sighted

Answer 9

their eyeball is too short or the lens can not focus light rays onto the retina

Question 10

give the near point and far point of our vision

Answer 10

near point-20cm

far point-infinity

Question 11

which two parts of the eye refract light before it arrives at the retina

Answer 11

the lens and the cornea

Question 12

which part of the eye changes the shape of the lens to focus close by and far away objects

Answer 12

ciliary muscles

Question 13

how can a lens be made thinner and flatter but still have the power needed to refract correctly

Answer 13

lens must have a higher refractive index

Question 14

2 factors affecting power of a lens

Answer 14

the refractive index

thickness of the lens

Question 15

what is an X-ray

Answer 15

a very high frequency electromagnetic wave

Question 16

what is the distance from a lens to the principle focus or focal point called

Answer 16

the focal length

Question 17

what does the power of a lens tell you

Answer 17

how much the lens bends light rays

Question 18

3 things that affect a lenses power

Answer 18

thickness
curvature
refractive index

Question 19

what type of lens is found in a magnifying glass

Answer 19

a convex lens- or converging lens

Question 20

the nature of an image is described in three ways

Answer 20

• virtual or real
• inverted or upright
• magnified x?

Question 21

why does the shape of the lens in the eye need to be changed

Answer 21

to allow light rays to focus on the retina from objects close by (thick lens) and far away (thinner lens)

Question 22

what happens to a light Ray in an endoscope

Answer 22

light is totally internally refracted because it reflects from the optical fibre of an angle larger than the critical angle

Question 23

medical usage of a laser

Answer 23

an energy source used for cutting skin tissue,burning cells and sealing blood vessels

Question 24

why does light totally internally refract in an optical fibre

Answer 24

the light hits the edge of the fibre at an angle bigger than the critical angle and reflects rather than refracts

Question 25

4 properties of X-rays

Answer 25

• absorbed by bone and metal
• wavelength is the diameter of an atom
• transmitted through soft tissue/skin
• they affect photographic film