P3.1 Medical applications of physics

Question 1

What are x-rays part of?

Answer 1

The electromagnetic spectrum

Question 2

What do x-rays have?

Answer 2

A very short wavelength

Question 3

What do x-rays cause?

Answer 3

Ionisation

Question 4

X-rays are absorbed by…

Answer 4

Metal and bone

Question 5

X-rays are transmitted by…

Answer 5

Soft tissue

Question 6

What can x-rays be used to diagnose and treat?

Answer 6

Some medical conditions, e.g. CT scans, bone fractures, dental problems and killing cancer cells

Question 7

Do precautions need to be taken when x-ray machines and CT scanners are in use?

Answer 7

Yes

Question 8

What is the range of human hearing?

Answer 8

20 Hz to 20 000 Hz

Question 9

What can electronic systems be used to produce?

Answer 9

Ultrasound waves, which have a frequency higher than the upper limit of hearing for humans?

Question 10

What happens to ultrasound waves when they meet a boundary between two mediums?

Answer 10

They are partially reflected

Question 11

What can the time taken for reflections to reach a detector determine?

Answer 11

How far away the boundary is

Question 12

What is the equation for distance between interfaces in various media?

Answer 12

s = v x t

Question 13

What does the s stand for?

Answer 13

Distance

Question 14

What does the v stand for?

Answer 14

Speed

Question 15

What does the t stand for?

Answer 15

Time

Question 16

Ultrasound waves can be used in…

Answer 16

Medicine, e.g. pre-natal scanning and the removal of kidney stones

Question 17

What is refraction?

Answer 17

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

Question 18

How does a lens form an image?

Answer 18

By refracting light

Question 19

What happens in a convex or converging lens?

Answer 19

Parallel rays of light are brought to a focus at the principal focus

Question 20

What is the distance from the lens to the principal focus called?

Answer 20

The focal length

Question 21

What is the calculation for refractive index?

Answer 21

sin i
Refractive index = ———
sin r

Question 22

What is the nature of an image defined by?

Answer 22

Its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual

Question 23

What is the nature of an image produced by a converging lens at 2F?

Answer 23

Same size, inverted, real

Question 24

What is the nature of an image produced by a converging lens further than 2F?

Answer 24

Diminished, inverted, real

Question 25

What is the nature of an image produced by a converging lens close than 2F?

Answer 25

Magnified, upright, vitrual

Question 26

What can a converging lens be used as?

Answer 26

A magnifying glass

Question 27

What is the nature of an image produced by a concave lens?

Answer 27

Virtual, upright and diminished

Question 28

How is magnification calculated?

Answer 28

image height Magnification = --------------------- object height

Question 29

What is the function of the cornea in the eye?

Answer 29

Refracts light as it enters the eye

Question 30

What is the function of the iris in the eye?

Answer 30

Controls how much light enters the pupil

Question 31

What is the function of the pupil in the eye?

Answer 31

Allows light to pass through as it enters the eye

Question 32

What is the function of the lens in the eye?

Answer 32

Refracts light and focuses it onto the retina. The amount of refraction can be adjusted by altering the thickness and curvature of the lens

Question 33

What is the function of the ciliary muscles in the eye?

Answer 33

Adjust the shape of the lens to make it more or less curved, so as to increase or decrease the refraction of light

Question 34

What is the function of the suspensory ligaments in the eye?

Answer 34

Slacken or stretch as the ciliary muscles contract or relax, to adjust the thickness and curvature of the lens

Question 35

What is the function of the retina in the eye?

Answer 35

Contains the light receptors, which trigger electrical impulses to be sent to the brain when light is detected

Question 36

What does correction of vision use?

Answer 36

Convex and concave lenses to produce an image on the retina

Question 37

What is long-sightedness caused by?

Answer 37

The eyeball being too short or the eye lens being unable to focus

Question 38

What is short-sightedness caused by?

Answer 38

The eye ball being too long or the eye lens being unable to focus

Question 39

The eyes can focus on objects between the...

Answer 39

Near point and the far point

Question 40

What is the near point?

Answer 40

Approximately 25 cm

Question 41

What is the far point?

Answer 41

Infinity

Question 42

What is the structure of the eye similar to?

Answer 42

A camera

Question 43

What is the camera's version of the retina?

Answer 43

The film or the CCD's

Question 44

What equation is the power of a lens given by?

Answer 44

1 P = ----- f

Question 45

What does the p stand for?

Answer 45

Power in dioptres, D

Question 46

What does the f stand for?

Answer 46

Focal length in metres, m

Question 47

What is the power of a converging lens?

Answer 47

Positive

Question 48

What is the power of a diverging lens?

Answer 48

Negative

Question 49

What is the focal length of a lens determined by?

Answer 49

The refractive index of the material from which the lens is made and the curvature of the two surfaces of the lens

Question 50

For a give focal length, the greater the refractive index...

Answer 50

The flatter the lens. This means that the lens can be manufactured thinner

Question 51

What is the total internal reflection?

Answer 51

Beyond the critical angle, when all waves reflect back into the glass

Question 52

What is the critical angle?

Answer 52

When the angle of incidence is equal to 90 degrees

Question 53

What is the equation for total internal reflection and the critical angle?

Answer 53

1 refractive index = ----------- sin c

Question 54

What does the c stand for?

Answer 54

Critical angle

Question 55

What can visible light be sent along?

Answer 55

Optical fibres

Question 56

What can a laser be used for?

Answer 56

Cutting cauterising and burning

Question 57

An endoscope uses optical fibres, what is an endoscope used for?

Answer 57

Internal imaging