Physics P3 1.4 The endoscope.

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What is the critical angle?
The critical angle is the angle of incidence of a light ray in a transparent substance which produces refraction along the boundary.
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How is the critical angle related to the refractive index?
By the equation n = 1 over sin c (look up).
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What is n in the equation n = 1 over sin c?
n is the refractive index.
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What is c in the equation n = 1 over sin c?
c is the critical angle.
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When does total internal reflection occur?
When the angle of incidence of a light ray in a transparent substance is greater than the critical angle.
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What is an endoscope used for?
To see inside the body directly.
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What will happen to a light ray when it crosses from glass to air?
It will refract, it is refracted away from the normal. A partially reflected ray is also seen.
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When a light ray crosses from glass to air, what happens if the angle of incidence in the glass is gradually increased?
The angle of refraction increases until the redacted ray emerges along the boundary.
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What is the angle of incidence called when the refracted ray emerges along the boundary?
This angle of incidence is called the critical angle, c.
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What happens if the angle of incidence is increased beyond the critical angle?
The light ray undergoes total internal reflection.
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What happens when total internal reflection occurs?
The angle of reflection is equal to the angle of incidence.
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Why is an endoscope a particularly useful device to see inside a patient's body?
It can be used to look inside a patient's body without cutting it open or when performing keyhole surgery.
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How does an endoscope work?
It contains bundles of optical fibres. These are very thin, flexible glass fibres. Visible light can be sent along the fibres by total internal reflection.
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How can laser light be used as an energy source in an endoscope?
To carry out some surgical procedures such as cutting, cauterising and burning.
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Why is the colour of the laser light relevant when using laser light to carry out procedures in an endoscope?
It is matched to the type of tissue to produce maximum absorption. Eye surgery on the retina in the eye can be carried out by using laser light that passes straight through the cornea at the front of the eye but is absorbed by the retina at the back.
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Total internal reflection only takes place...?
For a ray travelling from a more dense to a less dense material e.g. from glass to air.
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What is the critical angle for glass of refractive index 1.5?
42 degrees.
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What is an optical fibre?
A very thin, flexible glass fibre.
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**LOOK UP DIAGRAMS OF REFRACTION AND TOTAL INTERNAL REFLECTION**
**LOOK UP LIGHT RAYS IN AN OPTICAL FIBRE**
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Other cards in this set

Card 2

Front

How is the critical angle related to the refractive index?

Back

By the equation n = 1 over sin c (look up).

Card 3

Front

What is n in the equation n = 1 over sin c?

Back

Preview of the front of card 3

Card 4

Front

What is c in the equation n = 1 over sin c?

Back

Preview of the front of card 4

Card 5

Front

When does total internal reflection occur?

Back

Preview of the front of card 5
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