Radiation In Treatment And Medicine

Question 1

How do fibre optics work

Answer 1

Total internal refraction. The incidence ray is greater than the critical angle. This means none of the light is refracted, it reflects on the boundary. The ange of reflection is greater than critical angle so it reflects again until it come out the end.

Question 2

Formula for intensity

Answer 2

Power of incident radiation/distance squared
Measured in watts per meter squared
W/m^2

Question 3

What is the definition of radiation

Answer 3

Energy carried by waves or particles from a source

Question 4

What are the parts of the eye and uses

Answer 4

Optic never, takes electrical signals from retina to brain
Cornea, slightly refracts light towards the lens
Ring of ciliary muscle, contract to make it thicker, relax to pull lens thinner
Iris, controls amount of light reaching the lens so retina doesn’t get damaged
Retina, converts the light into electrical signals that can be interpreted by our brain
Lens, focus’ the light onto the retina

Question 5

What is the far point and what is ours

Answer 5

The furthest you can focus, ours is at infinity

Question 6

What is near point

Answer 6

The closest you can look at something without it being blurred

Question 7

Why does the lens need to change tickness

Answer 7

To make the light refract more or less so that the focal point is on the retina, not before or after or the image would be blurred

Question 8

What does it mean if someone is short sighted and how can it be corrected and why are the short sighted

Answer 8

They can see close objects but distant are too far as there lens doesn’t thin enough so the focal point is before the retina so it’s blurred. To correct it a diverging lens can be used to bend the light out before it enters the eye.

Question 9

What does it mean if someone is long sighted and how can it be corrected and why are they long sighted

Answer 9

Means they can focus on distant objects, just not close. This is because there lens isn’t thick enough when looking at things close so the focal point would be behind the retina so it’s blurred. To correct it, a converging lens is used to bend the light towards the eye before it enters it

Question 10

What does laser eye surgery do

Answer 10

It precisely changes the shape of the cornea so the focal point of the light can be altered so it always falls onto the retina

Question 11

Where is the focal point of a diverging lens

Answer 11

In front of the lens, where the rays seem to have come from if the lens wasn’t there after they have been bent

Question 12

What is the unit and formula for po wear of a lens

Answer 12

Power of lens = 1/focal length, metres

Measured in dioptres D

Question 13

What is the lens equation

Answer 13

1/f = 1/u + 1/v

Where u is object distance, image distance is v and focal length is f

Question 14

If an object is 10cm from a lens with focal length 5cm, where will the image be

Answer 14

1/v = 1/f - 1/u
1/v = 1/5 - 1/10 = 1/10 so image is 10 cm away, as result is positive, imgage is real

Question 15

What is the law of reflection

Answer 15

Angle of incidence = angle of reflection
, angle of incidence, angle light hits object against the normal , angle of reflection, angle it reflects away against the normal

Question 16

Which direction will a wave refract in a denser medium and a less dense one

Answer 16

Towards the normal in denser and away in less dense

Question 17

What is snells law

Answer 17

Sin I / sin r = nr/ni
I = angle of incidence
R = angle of reflection
nr = refractive index of medium ray travelling into
ni = refractive index of medium ray travelling from

Question 18

A light ray approaches a glass block at 30 degrees to the normal. The refractive index of air is 1 and glass is 1.5. What angle will the light be refracted at

Answer 18

Sin30 / sin r = 1.5/1
Sin 30/ 1.5 = sin r = .33
Sin (-1) 0.33 = 19.3 degrees

Question 19

What is the critical angle and why is it important

Answer 19

An angle that if a ray hits an object at the critical angle, the light will run along the boundary of the medium, if angle of incidence is greater than dirt angle then it will all be reflected, total internal reflection, if it’s less, some will reflect, some will refract

Question 20

What is total internal reflection

Answer 20

When angle of incidence is greater than critical angle, all light is reflected

Question 21

How does a car rain detector work

Answer 21

The detector produces and infrared ray at an angle greater than the critical angle of the glass windscreen so it is totally internally reflected. This infrared is detected, but when it rains, the water on the glass changes the crit angle so some of the infrared is refracted so not all of it is reflected so not all is detected. This is detected so the window wipers are turned on

Question 22

How do optical fibres work

Answer 22

Has a low critical angle so light angle of incidence will always be greater than critical angle so total internal reflection will keep happening until it exits the end

Question 23

How does an endoscope work

Answer 23

2 fibre optic cables and an eyepiece
Light goes down one cable and into the patient, this light reflects of the inside of the patient and back into the other optic Calle, this light travels along it into the eyepiece and into the doctors eye

Question 24

How can ultrasound be used

Answer 24

Sound higher than 20000Hz
Device both transmits and detects it
Send out ultrasound, when sound passes different tissue, some of it is reflected, some refracted. Detector can build an image using the reflected ultrasound. Can be used to find dense kidney stones then high intensity ultrasound can be used to break them up as lots of energy