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P3 Topic 1: Radiation in treatment and medicine
Radiation in Medicine

Both ionising and non-ionising radiation is used in medicine. Their uses aren't always straightforward and
sometimes compromises have to be made.
For example, ionising radiation makes a clear image of the inside of the body but can damage the…

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Generally, the denser the medium the more radiation will be absorbed thus decreasing the intensity of the

Intensity = Power of incident radiation per unit area

The more intense the radiation, the more energy it carries per second or the higher the power. Similarly, the
higher the power the…

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The near point is the closest distance that the eye can focus on. For the average adult that is 25cm.

Short-sighted people

Short-sighted people cannot focus on objects that are far away ­ this happens if their far point is closer than
Images of distance objects are brought into…

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Contact lenses or Laser eye surgery

Contact lenses: The cornea does most of the focussing for the eye, and when it's the wrong shape it can be
too weak or too powerful making it potentially responsible for both long and short sight. Contact lenses sit
on top of the cornea…

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Different lenses

There are two main types of lens ­ converging and diverging.
Converging lens are convex and they cause parallel rays of light to converge to a focus at the lens focal point
Diverging lens are concave and cause parallel rays of light to diverge. The focal point…

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The position of the object affects the image

Position of object At 2F Between F and 2F Nearer than F
Real or virtual Real Real Virtual
Image orientation Inverted Inverted Right way up
Image size Same as object Bigger than object Bigger than object
Image position At 2F Beyond…

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Diverging lenses always produce a virtual image.
The image is right way up, smaller than the object and on the same side of the lens as the object no matter
where it is.

Power and the Lens Equation

The focal length is related to power. The more powerful the lens,…

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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 internal reflection.
If the angle of incidence is greater than the critical angle no light comes out. It's all internally reflected i.e.
total internal reflection.


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