Topic 1 - Radiation And Treatment Flashcards
What are X-rays
High energy EM waves that get absorbed by dense materials
Are X-rays ionising or non ionising
Ionising
What can X-ray photographs diagnose
Bone fractures
What does CAT scans stand for
Computerised axial tomography
What do CAT scans produce
2D slice through the body
What do CAT scans use
Intense beams of X-rays
What can CAT scans do that x rays can’t
Image soft tissue as well as bones
What do endoscopes use to see inside the body
Optical fibres
What type of electromagnetic Ray do endoscopes use
Visible light
What do endoscopes help to reduce the use of
Invasive surgery
What frequency does ultrasound use
Above 20 kHz
What can ultrasound be used for
Breaking down kidney stones into sand like particles
Pre natal scan of a foetus
Measuring the speed of blood flow
What is radiation
Energy that originates from a source
What does the intensity of radiation depend on
Distance from a source
What it’s passing through
Unless passing through a vacuum some of the radiation will…..
Always be absorbed by the medium
Intensity equals
Power divided by area
Refraction is……
A change in direction caused by a change in speed
If a wave hits a boundary along the norm….
It will not change direction
What are the two main types of lenses
Converging and diverging
Or convex and concave
Convex lense cause light rays to…..
Converge to a focus at the lens focal point
Concave lens cause light rays to…
Spread out
The focal point of a diverging lens is the point where………
Rays hitting the lens parallel to the axis appear to come from
What are the three rules for refraction in a converging lens
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 will carry on in the same direction.
At 2F the object will be……
Real, Inverted, same as object, at 2F
An object between F and 2F will be….
Real, inverted, bigger than object, beyond 2F
An object nearer than F will be
Virtual right way up, bigger than object and same side of the lens
What are the three rules of a diverging lens
An incident Ray parallel to the axis refracts through the lens travels in line with 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
An diverging lens always produces….
A virtual image that is the right way up, smaller and on the same side of the lens
The power of a converging lens is always
Positive
The power of a diverging lens is always
Negative
Power of lens equals
1 divided by focal length
What does the iris do
Coloured part of the eye
Made up of muscles that control the size of the pupil
Controls how much light enters the eye
What does the cornea do
The transparent window with a convex shape it does most of the eyes focusing
How is light focused on by the retina
By the lens and the cornea working together
What kind of power does the cornea have
Fixed
What is the lens controlled by
Ciliary muscles
What is the retina covered in
Light sensitive cells
What is the furthest point your eye can see comfortable
Infinity
What is the nearest point your eye can see
25cm
Short sighted people cant…
Focus on objects that are far away
What are x rays used for
Medical imaging
Why are some people short sighted
Cornea and lens too powerful or eyeball is too long
Ciliary muscles can’t relax enough
What can’t long sighted people do
Can’t focus on things close up
Why are some people long sighted
Cornea or lens too weak
Eyeball is too short
Ciliary muscles can’t contract enough
In long sighted people the I shed of near object are….
Brought into focus behind the retina
How do you fix short sightedness
Diverging or concave lens
Brought into focus on the retina
How can you correct long sightedness
Convex lens
Brought into focus earlier
How else can you fix a vision defect
Contact lenses which compensate the fault of the eye shape
Laser eye surgery which permanently changed the shape of the cornea
What is Snells law
When an incident Ray passed into a material the angle of incidence angle of refraction and refractive index are related by this formula
n = sin i
————-
sin r
What is the critical angle
90 degrees
If the angle of incidence is less than the critical angle…..
Most of the light passes out but a little bit of it is internally reflected
If the angle of incidence is equal to the critical angle
The emerging Ray comes out along the surface there’s quite a bit of reflection
If the angle of incidence is greater than the critical angle then
No light comes out
Total internal reflection
You can find critical angles using…
Snells law
Nr is ……
The refractive index of the stuff the lights travelling towards
Ni is
The refractive index of the material the light starts from
How do optical fibres work
Carry visible lights and can be used in medical diagnosis and communications technology
Work because of total internal reflection light waves are reflected off the sides of a thin inner core of plastic or glass
Reflected repeatedly until it reaches the other end
