Radiation And Treatment Flashcards
What is ionising radiation
High energy particles that collide with things at high speed knocking electrons from them
How are x rays used in medicine
X rays are high energy em waves
They’re absorbed into high density material
X-rays are used to diagnose things like bone fractures
But they’re a health risk to anyone who uses them because they’re ionising
What are cat scans
They used X-rays to produce an image of a 2D slice through the body
They are strongly ionising and use intense beams of X-rays
They can be used to image soft tissue as well as bones
What are endoscopes
They use visible light reflected along optical fibres
They can be used to see inside the patient and investigate problems without invasive surgery
They can be used for keyhole surgery
How are kidney stones broken down
They are hard masses that block the urinary tract
Ultrasound beams are high energy and are directed at at the stone to turn it into sand like particles
It is relatively painless and doesn’t need surgery
What happens in prenatal scanning of a foetus
Ultra sound imaging is used because the waves are reflected off different tissue boundaries the times and echoes are recorded by a computer to form an image on a screen
How is the speed of blood flow measured
Ultrasound works in real time so it can show things changing and moving
Ultra sound can be used to measure the speed of blood flow and identify any blockages in veins and arteries particularly in the heart and liver
What is radiation
Energy that originates from a source
What effects the intensity of radiation
It decreases as the distance from the radiation increases
What it’s passing through, unless it’s passing through a vacuum some of the radiation will always be absorbed usually the more dense the medium the more radiation absorbed
The surface area of the object
What is the intensity of radiation
The more intense the more energy carried per second or the higher the power
The higher the power the mor energy gets transferred per second when hitting an object
Intensity (w/m2)=
Power (w) /area (m2)
What is refraction
When radiation changes direction as it enters a different medium causing it to change speed
What happens in refraction
When the waves do into a denser medium they slow down and bend towards the normal because the side nearest the normal slows first
If the wave hits a boundary at 90 it will not change direction just slow down
When the light hits a medium some of it is reflected some of it is refracted
What does a converging lenses do
They cause parallel rays to move together and focus at a point (the focal point)
What does a diverging lens do
It is concave so it caves inwards and causes parallel rays of light to spread out
The focal point is where the rays appear to come from once they have passed through the lens
What are the rules of refraction in a converging lense
An incident ray parallel to the axis passes straight 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
How to use a ray diagram to find the position and size of an image
Draw a line from the top of the object to the lens parallel to the image p
Draw a line from the top of the object to the middle of the lens
The ray parallel to the axis is refracted through the focal point
The line passing through the centre of the lens doesn’t bend
Where the two lines meet is the top of the image
The image of an object at 2f is
Real
Inverted
The same size
At 2f on the other side of the lens
The image of an object between F and 2F is
Real
Inverted
Bigger than the object
Beyond 2f
The image of an object nearer than F is
Virtual
The right way up
Bigger than the object
On the same side of the lens as the object
If the lines don’t meet at a point then trace them back
What are the three rules for refraction in a diverging lens
An incident ray parallel to the axis refracts through the lens and 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
How to draw a ray diagram for an image through a diverging lens
Draw a line from the top of the object parallel to the axis to the lens
Draw a line from the top of the object to the centre of the lens
The incident that is parallel to the axis is refracted so it appears to have come from the focal point
The ray passing through the middle doesn’t bend
Mark where the refracted rays would meet when traced back this is where the top of the image is
What image is produced by a diverging lens
A virtual image
It’s the right way up
On the same side as the object
Smaller than the object
What is the power of a lens
The more powerful a lens the more quickly it converges the rays of light so the shorter the focal length
The power of a converging lens is always positive the power of a diverging lens is always negative
The more curved the lens the more powerful it is
Power of lens
1/ focal length
What does 1/f = 1/u + 1/v mean
If the object Is further than one focal length away it is real
If the object is closer than the image it is virtual
U is the distance from the centre of the lens tot e object
V is the distance between the image and the lens
This formula give the relation ship between the position of the image, the object and the focal length
V is positive if the image is real it’s negative if the image is virtual
All distances are in m
What is the iris
The coloured part of the eye it is made up of muscle that controls the size of the pupil
What is the pupil
A hole in the middle of the iris that controls how much light enters the eye
What is the cornea
A transparent window at the front of the eye in a convex shape it does most of the focusing
It has a fixed power
What is the retina
Where the light is focused
It is covered in light sensitive cells and detects light and sends signals to the brain via the optic nerve
What is the lens of the eye
It works with the cornea to focus the light
It can change its power by changing shape it is controlled by ciliary muscles
What are ciliary muscles
They control the shape of the lens
When they contract the lens becomes fat and spherical
When they relax the lens becomes thinner and flatter
What is the far point in the eye
The far point it the furthest distance the eye can focus clearly for normally sighted people this is Infinity
Wha put is the near point of the eye
The closest distance the eye can focus on
Usually around 25cm
What is short sightedness
People can’t focus on objects far away so their far point is closer than infinity
Images of distant objects are brought into focus in front of the retina
It can happen if the cornea and lens are too powerful or the eye is too long or the ciliary muscles might not be able to relax enough to focus the light on the retina
What is longsightedness
When people can’t focus on near objects so their near point is further than 25cm away
Images of near objects are brought into focus behind the retina
It could happen if the cornea and lens are too weak or the eyeball is too short the ciliary muscles might not be able to contract enough to change the shape of the eye
It is more common in old people when the eye gets stiffer and the ciliary muscles become weaker
How is short sightedness corrected
Glasses with diverging lenses
The correcting lens must have a focal point at the eyes faulty point
This means that the objects at infinity that were out of focus now seem to be in focus at the far point
How is long sight corrected
The near point can be brought down to 25cm by using a converging lens it produces a virtual image at 0.25m away from the eye
This means that near objects are in focus
How is sight corrected using contact lenses
Contact lenses sit on top of the cornea and are shaped to compensate for the fault in the lens or cornea they can be converging or diverging
What happens in laser eye surgery
A laser is used to vaporise tissue and change the shape of the cornea when taking a layer of cells away from the cornea shortsightedness is corrected and changing the shape to make it more powerful will correct long sight
The surgeon can precisely control how much tissue the laser takes off
What are the pros and cons of glasses
They’re cheap
They can treat very severe cases
They’re heavy and uncomfortable
What are the pros and cons of contact lenses
They’re convenient
Cheap
Lightweight and invisible
Can be uncomfortable or fall out and can cause eye infections
What are the pros and cons of laser eye surgery
Can fix vision
Expensive There's a risk of complication It could make your sight worse Infection risk Will not stop eyesight from deteriorating over time
What is a refractive index
The amount of light refracted depends on the refractive index
Glass is dense and has a high refractive index
The refractive index of air and a vacuum is 1
What is snells law
When an incident ray passes into a material the angle of incidence the angle of refraction and the refractive index are related by the formula
N = sin I / sin R
What is total internal reflection
When the critical angle is reached and no light leaves the medium
What is the critical angle
When a light leaves one medium into a less dense one it speeds up and bends away from the normal
If you keep on increasing the angle of incidence the angle of refraction gets closer to 90
At 90 the critical angle is reached and the light is refracted along the medium
If the angle of incidence is less than the critical angle
Most of the light passes out of the medium and is refracted
If the angle of incidence is equal to the critical angle
The emerging ray comes out along the surface and there’s quite a lot of reflection
If the angle of incidence is greater than the critical angle
No light comes out at all and total internal reflection happens
How do you find out the critical angle
Using snells law
When the incident angle is equal to the critical angle the angle of refraction is 90
Sin 90 = 1 so the right hand side becomes sin C where c = the critical angle so
Sin C = nr (reflective index of the medium the lights travelling towards) // ni (reflective index of the material the light travels from)
How do optical fibres work
The light waves are reflected off the sides of a thin inner core of glass or plastic
The wave enters at one end and and is continually reflected until it leaves at the other end
They must be narrow enough to keep the angles above the critical angle so the fibre can’t bend too sharply anywhere
How do endoscopes work
There’s two bundles of optical fibres one to carry the light to the area and one to carry the image back
The image can be seen through an eyepiece of displayed as a full colour moving image on a screen
This makes keyhole surgery possible
