Health Physics: Light and Sight
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what is refraction?
the bending of light as it passes from one material into another
what happens during refraction?
- When light passes from air into glass it bends towards the normal
- when light passes from glass into air it bends away from the normal
what does a convex lens do?
causes rays of light to be brought to a focus
what does a concave lens do?
causes rays of light to spread apart
how is light focused on the retina of the eye?
by the cornea and lens
what is focal length?
the distance between a lens and the point where parallel rays of light are brought to a focus
how can the focal length of a convex lens be measured experimentally?
- by placing the lens in front of a screen and moving the lens until a sharp image of a distant object is obtained on the screen
- then measuring the distance from the lens to the screen
what is the power of a lens measured in?
what does the image that the eye forms look like?
- smaller than the object
convex lenses have what power?
concave lenses have what power?
what happens with people with short-sight?
- unable to focus on distant objects clearly
- corrected by using a concave lens
what happens with people with long-sight?
- unable to focus on close objects clearly
- corrected by using a convex lens
why does short-sight occur?
rays of light from a distant object are brought to a focus in front of the retina
why does long-sight occur?
rays of light from a nearby object are brought to a focus behind the retina
what is transmitted along optical fibres?
what are endoscopes used for?
- to view the insides of a patient without the need for surgery
- optical fibres carry the light down into the patient
- a second bundle of fibres is then used to send the image back to the surgeons eye
- the fibres are flexible, so they can be moved around inside the patient
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