P3.1 Radiation In Treatment And Medicine

Question 1

What is visible light used for in medicine?

Answer 1

In endoscopes to see inside someone

Question 2

What are X-rays used for in medicine?

Answer 2

X-Ray photography and CAT scanners

Question 3

What are Gamma rays used for in medicine?

Answer 3

PET Scanners

Question 4

What is Ultrasound used for in medicine?

Answer 4

Breaking down kidney stones
Pre-natal scanning of a foetus
Measuring the speed of blood flow

Question 5

Why are X-rays used as little as possible?

Answer 5

It is ionising and dangerous for the patients cells.

Question 6

What is the definition of radiation?

Answer 6

Energy emitted from a source

Question 7

What does the intensity of radiation depend on?

Answer 7

The distance from the source

What its passing through

Question 8

What medium helps reduce the intensity of radiation?

Answer 8

A dense medium

Question 9

What is the formula for radiation intensity?

Answer 9

Intensity = Power/Area

Question 10

What are the units for intensity of radiation?

Answer 10

W/m2

Question 11

What is refraction?

Answer 11

A change in direction caused by a change in speed

Question 12

How does light refract?

Answer 12

When it enters a denser medium, it bends towards the normal

When it enters a less dense medium, it bends away from the normal.

Question 13

What are the threw rays called in refraction?

Answer 13

Incident ray
Refracted ray
Emergent ray

Question 14

What is a converging lens?

Answer 14

A lens that causes parallel light rays to come together at the focal point. It produces a real image.

Question 15

What is a diverging lens?

Answer 15

A lens that causes parallel light rays to spread out. It produces a virtual image.

Question 16

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

Answer 16

1. An incident ray parallel to the axis refracts through the lens and passes through the focal point.
2. An incident ray passing through the focal point before entering the lens will refract through the lens amd travel parallel to the axis.
3. An incident ray passing through the centre of the lens carries on in the same direction.

Question 17

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

Answer 17

1. An incident ray parallel to the axis refracts through the lens and travels in line with the focal point (so it appears to have come from the focal point)
2. An incident ray passing towards the focal point refracts through the lens and travels parallel to the axis
3. An incident ray passing through the centre of the lens carries on in the same direction.

Question 18

What is the equation for power of a lens?

Answer 18

Power = 1/focal length

Question 19

For the lens equation, what units are used?

Answer 19

Metres, m

Question 20

What are the parts of the eye?

Answer 20

Lens, cornea, iris, ciliary muscles, retina, optical nerve, pupil.

Question 21

What does a light ray pass through first and finish at as it enters the eye?

Answer 21

Cornea, pupil, lens, retina.

Question 22

What is the far point?

Answer 22

The furthest the eye can see. For humans, it is infinity.

Question 23

What is the near point?

Answer 23

The nearest the human eye can clearly see. For humans, it is about 25cm.

Question 24

What is short sight?

Answer 24

When a person can clearly see near objects but not far objects. The lens is too powerful so the image is formed in front of the retina.

Question 25

What is long sight?

Answer 25

A long sighted person can focus on far objects but not on near objects. The lens is not powerful enough and the image is formed behind the retina.

Question 26

How do you correct general sight defects?

Answer 26

Laser eye surgery
Glasses
Contact lenses

Question 27

How is short sight corrected?

Answer 27

With a diverging lens or by slimming the cornea with laser eye surgery.

Question 28

How is long sight corrected?

Answer 28

Using a converging lens or laser eye surgery.

Question 29

What are the pros and cons for glasses?

Answer 29

Pros: Cheap, can treat severe problems
Cons: Heavy, uncomfortable, unaesthetic, impractical for sports.

Question 30

What are the pros and cons for contact lenses?

Answer 30

Pros: Cheap, convenient, lightweight, invisible.
Cons: uncomfortable, can fall out, can cause infection.

Question 31

What are the pros and cons for laser eye surgery?

Answer 31

Pros: can permanently fix problems
Cons: expensive, complication

Question 32

What is the refractive index?

Answer 32

An indication of how much light the material will refract.

Question 33

What does Snell’s law say?

Answer 33

Sin i / Sin r = n

Question 34

What does Snell’s law? (4 values)

Answer 34

Sin i nr
—– = —
Sin r ni

Question 35

What is total internal reflection (TIR) ?

Answer 35

When a light ray hits a material at an angle greater than the critical angle, the light is totally reflected and nor refracted.

Question 36

What is the critical angle?

Answer 36

An angle that when a light ray enters an object at that angle, it travels along the boundary.

Question 37

How do you find the critical angle using Snell’s law?

Answer 37

SinC = nr/ni

Question 38

What is an optical fibre?

Answer 38

A cable that can carry visible light along it inside it by TIR.

Question 39

What are the uses of Optical fibres?

Answer 39

Broadband cables

Endoscopes

Question 40

What are the advantages of endoscopes?

Answer 40

They have enabled keyhole surgery - where surgeons can operate using only tiny holes.