P3.1 Radiation In Treatment And Medicine Flashcards
What is visible light used for in medicine?
In endoscopes to see inside someone
What are X-rays used for in medicine?
X-Ray photography and CAT scanners
What are Gamma rays used for in medicine?
PET Scanners
What is Ultrasound used for in medicine?
Breaking down kidney stones
Pre-natal scanning of a foetus
Measuring the speed of blood flow
Why are X-rays used as little as possible?
It is ionising and dangerous for the patients cells.
What is the definition of radiation?
Energy emitted from a source
What does the intensity of radiation depend on?
The distance from the source
What its passing through
What medium helps reduce the intensity of radiation?
A dense medium
What is the formula for radiation intensity?
Intensity = Power/Area
What are the units for intensity of radiation?
W/m2
What is refraction?
A change in direction caused by a change in speed
How does light refract?
When it enters a denser medium, it bends towards the normal
When it enters a less dense medium, it bends away from the normal.
What are the threw rays called in refraction?
Incident ray
Refracted ray
Emergent ray
What is a converging lens?
A lens that causes parallel light rays to come together at the focal point. It produces a real image.
What is a diverging lens?
A lens that causes parallel light rays to spread out. It produces a virtual image.
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.
- An incident ray passing through the focal point before entering the lens will refract through the lens amd travel parallel to the axis.
- An incident ray passing through the centre of the lens carries on in the same direction.
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 (so it appears to have come 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.
What is the equation for power of a lens?
Power = 1/focal length
For the lens equation, what units are used?
Metres, m
What are the parts of the eye?
Lens, cornea, iris, ciliary muscles, retina, optical nerve, pupil.
What does a light ray pass through first and finish at as it enters the eye?
Cornea, pupil, lens, retina.
What is the far point?
The furthest the eye can see. For humans, it is infinity.
What is the near point?
The nearest the human eye can clearly see. For humans, it is about 25cm.
What is short sight?
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.
What is long sight?
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.
How do you correct general sight defects?
Laser eye surgery
Glasses
Contact lenses
How is short sight corrected?
With a diverging lens or by slimming the cornea with laser eye surgery.
How is long sight corrected?
Using a converging lens or laser eye surgery.
What are the pros and cons for glasses?
Pros: Cheap, can treat severe problems
Cons: Heavy, uncomfortable, unaesthetic, impractical for sports.
What are the pros and cons for contact lenses?
Pros: Cheap, convenient, lightweight, invisible.
Cons: uncomfortable, can fall out, can cause infection.
What are the pros and cons for laser eye surgery?
Pros: can permanently fix problems
Cons: expensive, complication
What is the refractive index?
An indication of how much light the material will refract.
What does Snell’s law say?
Sin i / Sin r = n
What does Snell’s law? (4 values)
Sin i nr
—– = —
Sin r ni
What is total internal reflection (TIR) ?
When a light ray hits a material at an angle greater than the critical angle, the light is totally reflected and nor refracted.
What is the critical angle?
An angle that when a light ray enters an object at that angle, it travels along the boundary.
How do you find the critical angle using Snell’s law?
SinC = nr/ni
What is an optical fibre?
A cable that can carry visible light along it inside it by TIR.
What are the uses of Optical fibres?
Broadband cables
Endoscopes
What are the advantages of endoscopes?
They have enabled keyhole surgery - where surgeons can operate using only tiny holes.
