Topic 1 - Radiation and Treatment

Question 1

What are x-rays used for in medicine

Answer 1

High energy EM waves that get absorbed by dense materials like bone and metal. This makes them good to take x-ray photographs that can be used to diagnose bone fractures. CAT scans

Question 2

How do CAT scans work?

Answer 2

use x-rays to produce an image of a 2D slice through the body. They use intense beams of x-rays that are strongly ionising. They can be used to see soft tissue as well as bones.

Question 3

What is an endoscope?

Answer 3

reflects visible light along optical fibres and can be used to see inside the patient to investigate problems without invasive surgery.

Question 4

What frequency is ultrasound

Answer 4

above 20 kHz

Question 5

What makes ultrasound safer than using x-ray and other ionising radiation

Answer 5

It isn’t ionising

Question 6

What are the uses of Ultrasound

Answer 6

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

Question 7

How does ultrasound break down kidney stone

Answer 7

Kidney stones are hard masses that can block the urinary track and be extremely painful. An ultrasound beam concentrates high energy waves at the stone and turns it into sand like particles, these pass out of the body in urine and is good because it doesn’t require surgery and is relatively painless.

Question 8

How is ultrasound used for pre natal scanning

Answer 8

Ultrasound imaging can be used to diagnose soft tissue problems and to perform prenatal scans of a foetus. The sound waves are reflected off the different tissue boundaries and the times and distributions of the echoes are processed by a computer to form an image on the screen.

Question 9

How is ultrasound used to measure the speed of blood flow

Answer 9

because it works in real time it can show things changing and moving which makes it useful for investigating problems with blood flow particularly in heart and liver. special ultrasound machines can measure the speed of the blood flow and identify any blockages in the veins and arteries.

Question 10

What is radiation

Answer 10

radiation is energy that originates from a source

Question 11

What does the intensity of radiation depend on?

Answer 11

Distance from the source and what it is passing through.

Question 12

What is radiation absorbed by?

Answer 12

Unless passing through a vacuum some radiation is absorbed by the medium its passing through. The more dense the medium the more radiation will be absorbed, decreasing the intensity

Question 13

What is the unit of intensity?

Answer 13

W/m2

Question 14

What is refraction

Answer 14

Change in direction due to a change in speed. When waves slow down the bend towards the normal, when they speed up they move away.

Question 15

What are the two types of lens

Answer 15

covering (convex) and diverging (concave)

Question 16

What do converging lenses do to light?

Answer 16

they make the light converge (come together) to focus at the focal point.

Question 17

What does a diverging lens do to light?

Answer 17

it makes the rays of light diverge (spread out)

Question 18

Where is the focal point of a diverging lens?

Answer 18

it is the point where rays hitting the lens parallel to the axis appear to come from, so behind the lens

Question 19

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

Answer 19

An incident ray parallel to the axis refracts through the lens and passes through the focal point on the other side.

An incident ray passing through the focal point before entering the lens will refract through the lens and travel parallel to the axis.

An incident ray passing through the centre of the lens carries on in the same direction.

Question 20

How can you use a ray diagram to find the position and size of an image through a converging lens

Answer 20

draw line from top of object that is parallel to axis to centre of lens then connect it to focal point and carry it on. Draw another line from top of object to middle of lens then carry it on until it crosses the other line. This is the top of the image.

Question 21

What are the three rules for refraction in a diverging lens

Answer 21

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 away from the focal point)

An incident ray passing towards the focal point refracts through the lens and travels parallel to the axis

An incident ray passing through the centre of the lens carries on in the same direction

Question 22

how do you draw a ray diagram for an image through a diverging lens

Answer 22

draw a line from the top of the object to the centre of the lens parallel to the axis. Draw another ray from the top of the object going through the centre of the lens. The incident ray thats parallel to the axis is refracted so appears to have come from the focal point, so draw a line to the focal point. The ray passing through the middle doesn’t bend. Mark where the rays meet and this is the top of the image. If the object is not on the axis then do the same for the bottom of the object.

Question 23

Is the image produced by a diverging lens real or virtual

Answer 23

virtual

Question 24

Does a powerful lens have a short or long focal length

Answer 24

short

Question 25

What is the power of a lens measured in

Answer 25

Dioptres (D)

Question 26

In the lens equation 1/f = 1/u + 1/v what do f, u and v stand for

Answer 26

f = focal length u = object distance v = image distance

Question 27

What is the iris?

Answer 27

Coloured part of eye Made of muscles that control the size of the pupil so determine how much light is let in.

Question 28

What is the cornea?

Answer 28

Transparent ‘window’ with a convex shape. Refracts light as it comes into the eye

Question 29

What is the lens in an eye

Answer 29

Transparent, bi-convex, flexible disc behind the iris attached by the suspensory ligaments to the ciliary muscles. Focuses light onto the retina.

Question 30

What is the retina

Answer 30

covered in light sensitive cells which detect light and send signals to the brain.

Question 31

what is the optic nerve

Answer 31

bundle of sensory neurones at back of eye that carries impulse from eye to brain

Question 32

What is the pupil

Answer 32

a small opening in the iris that lets light into the eye

Question 33

what are ciliary muscles

Answer 33

muscle that surrounds the lens to make it change shape to focus light onto the retina. When they contract the muscle becomes a more spherical shape.

Question 34

which two parts of the eye focus light

Answer 34

the cornea and the lens. the cornea has a fixed power but the lens can change its focusing power by changing shape.

Question 35

What is the far point

Answer 35

the furthest distance that the eye can focus on comfortably, for most people that is infinity.

Question 36

What is the near point

Answer 36

the closest distance that the eye can focus on. For the average adult that is around 25cm

Question 37

What happens with short sightedness

Answer 37

Short sighted people can’t focus on images that are far away so their near point is closer than infinity. Images of distant objects are focused in front of the retina. This happens because the cornea/lens is too powerful, the eyeball is too long, or the ciliary muscles can’t relax enough.

Question 38

What happens with long sightedness

Answer 38

Long sighted people can’t focus clearly on near objects because their near point is further away than usual. Images are focused behind the retina. This happens because the cornea/lens are too weak, the eyeball is too short, the ciliary muscles can’t contract enough to change the shape of the lens. It often occurs with old age because the lens becomes stiffer or the ciliary muscles become weaker.

Question 39

How do you correct short sightedness

Answer 39

a diverging lens with its focal point at the eyes faulty far point so objects at infinity seem to be in focus

Question 40

how do you correct long sightedness

Answer 40

a converging lense is used to produce a virtual image of objects 25cm away at the eyes near point. this means close objects now seem to be in focus at the near point.

Question 41

What are the methods to correct sight

Answer 41

glasses, contact lenses or laser eye surgery

Question 42

How do contact lenses work?

Answer 42

the cornea does most of the focusing in the eye and when it is the wrong shape it can be too weak or too powerful, and can be responsible for both long and short sight. Contact lenses sit on top of the cornea and are shaped to compensate for the fault, they can be converging or diverging.

Question 43

how does laser eye surgery work

Answer 43

a laser can be used to vaporise tissue, changing the shape of the cornea. Slimming it down makes it less powerful and can improve short sight. Changing the shape so that it is more powerful will improve long sight. The surgeon can precisely control how much tissue the laser takes off, completely correcting the vision.

Question 44

What are the things to consider when choosing treatment for sight problems

Answer 44

glasses are cheapest and can treat even severe eye problems, however some people find them heavy, uncomfortable, and don’t like the way they look. Can easily be changed if in need of different prescription

Contact lenses are convenient, relatively cheap, lightweight, and almost invisible. However they can be uncomfortable and sometimes fall out of your eye and cause eye infections if not looked after properly. Can easily be changed if in need of different prescription

Laser eye surgery has potential to properly fix vision so no need for glasses or contacts, however it can be expensive, there is a risk such as an infection, your eye could respond unexpectedly making your eyesight worse, not a permanent solution as eyesight may still deteriorate.

Question 45

What is refractive index.

Answer 45

Every transparent material has a refreactive index. It is a number given to it to desribe what happens to waves as they are refracted through it. Air has a refractive index of 1, glass slows waves down more so is higher (1.5 ish).

Question 46

What is snells law for going from air to glass

Answer 46

n = sin i/sin r

Question 47

What is snells law going from glass to air

Answer 47

n = sin r/sin i

Question 48

what is snells law to calculate critical angle

Answer 48

n = 1/sin c (going from air into something)

sin c = n₁/n₂

Question 49

what is critical angle

Answer 49

the angle for wich r=90. The light is refracted along the boundary.

Question 50

What happens if i is less than the critical angle

Answer 50

most of the light passes out but a little is internally reflected

Question 51

What happens if i is equal to the critial angle

Answer 51

the emerging ray comes out along the surface, theres quite a bit of internal reflection

Question 52

What happens if i is more than the critical angle

Answer 52

total internal reflection. no light comes out, it is all internally reflected.

Question 53

how do optical fibres use total internal reflection

Answer 53

optical fibres can carry visible light and can be used in medical diagnosis and communications. They work because of total internal reflection - light waves are reflected off the sides of the inner core of glass or plastic. the wave enters one end and is reflected repeatedly until it emerges at the other end. The fibre must be narrow enogh to keep the angles above the critical angle and the fibre mustn’t be bent too sharply.

Question 54

How do endoscopes work

Answer 54

an endoscope is a thin tube containing optical fibres that lets surgeons examine inside the body. They consist of two bundles of optical fibres - one to carry light to the area and one to carry an image back so it can be viewed. The image can be seen through an eyepiece of displayed as a full colour moving image on a tv screen.

Question 55

What are the advantages of using endoscopes

Answer 55

Surgeons can now perform many operations by only cutting small holes in people, this is called keyhole surgery.