Radiation In Treatment And Medicine Flashcards
How do fibre optics work
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.
Formula for intensity
Power of incident radiation/distance squared
Measured in watts per meter squared
W/m^2
What is the definition of radiation
Energy carried by waves or particles from a source
What are the parts of the eye and uses
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
What is the far point and what is ours
The furthest you can focus, ours is at infinity
What is near point
The closest you can look at something without it being blurred
Why does the lens need to change tickness
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
What does it mean if someone is short sighted and how can it be corrected and why are the short sighted
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.
What does it mean if someone is long sighted and how can it be corrected and why are they long sighted
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
What does laser eye surgery do
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
Where is the focal point of a diverging lens
In front of the lens, where the rays seem to have come from if the lens wasn’t there after they have been bent
What is the unit and formula for po wear of a lens
Power of lens = 1/focal length, metres
Measured in dioptres D
What is the lens equation
1/f = 1/u + 1/v
Where u is object distance, image distance is v and focal length is f
If an object is 10cm from a lens with focal length 5cm, where will the image be
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
What is the law of reflection
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
Which direction will a wave refract in a denser medium and a less dense one
Towards the normal in denser and away in less dense
What is snells law
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
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
Sin30 / sin r = 1.5/1
Sin 30/ 1.5 = sin r = .33
Sin (-1) 0.33 = 19.3 degrees
What is the critical angle and why is it important
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
What is total internal reflection
When angle of incidence is greater than critical angle, all light is reflected
How does a car rain detector work
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
How do optical fibres work
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
How does an endoscope work
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
How can ultrasound be used
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
