# P3 Chapter 1 Medical Applications in Physics Part 2

Topics covered:

-Correcting vision
-Total internal reflection
-Lasers

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What is the near and far point of a normal eye?
Near: 25cm Far: Infinity
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What can people with long-sight (hyperopia) not focus on?
Nearby objects
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What are the reasons for long sight?
Eyeball=too short and lens becomes too elastic=>not thick enough
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Therefore where is the light focused?
Behind the retina
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How do we treat long-sight with what power?
Use a converging lens which has positive power
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What can people with short-sight (myopia) not focus on?
Distant objects
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Therefore what is the far point?
Far point is less that infinity
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What are the reasons for short sight?
Eyeball=too long and lens is too thick
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Therefore where is the light focused?
On a point in front of the retina.
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How do we treat short sight and what is the power?
By using a diverging lens (partial unfocus) and negative power
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What happens to light when it is refracted with [i] being less than the critical angle?
Light changes direction and changes speed as it passes out.
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How much is internally reflected?
Little as most light passes out
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What happens to the light when [i] is equal to the critical angle?
Light skims surface of the glass.
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How much is internally reflected?
Quite a bit.
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What happens to light when [i] is more than the critical angle?
The ray is totally internally reflected. (Total internal reflection)
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What is the angle of reflection equal to?
Angle of refraction
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What does the value of the critical angle depend on?
The refractive index.
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What size critical angle do dense materials with high reflective index?
A low critical angle
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What is the formula for finding the critical angle/refracted index?
Refracted index, n=1/sin of critical angle, C
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What are some uses of total internal reflection?
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What are optical fibres good for?
Carrying light over LONG distances quickly
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What are the two bundles of optical fibres used for in the endoscope?
light and the image
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How do we see the image?
Through an eyepiece or on a TV screen
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What are lasers?
A narrow intense beam of light
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What are lasers used for?
Laser cutting, cauterisation, skin conditions, laser eye surgery
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## Other cards in this set

### Card 2

#### Front

What can people with long-sight (hyperopia) not focus on?

Nearby objects

### Card 3

#### Front

What are the reasons for long sight?

### Card 4

#### Front

Therefore where is the light focused?

### Card 5

#### Front

How do we treat long-sight with what power?