Refractive Index and Snells law Flashcards

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1
Q

Does Transparent material have refractive index

A

Yes, every transparent material has a refractive index

The refractive index of a transparent material tells you how fast light travels in that material.

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2
Q

what is the formula for refractive index?

A

refractive index, n = speed of light in a vacuum, c

speed of light in that material, v

n = c / v

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3
Q

Does light slows down more in water or glass?

A

Light slows down a lot in glass, so the refractive index of glass is high (around 1.5). The refractive index of water is a bit lower (around 1.33) — so light doesn’t slow down as much in water as in glass.

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4
Q

is the speed of light in air the same as in a vacuum,?.

A

The speed of light in air is about the same as in a vacuum, so the refractive index of air is 1.00 (to 2 d.p.).

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5
Q

what is snells law?

A

1) According to Snell’s law, the angle of incidence, angle of refraction and refractive index are all linked…

2 ) snells law says, when an incident ray passes into a material:

n = sin i / sin r

so if you know any of the two of n, i or r , you can work out the missing one

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6
Q

Practical experiment for refractive index and snells law

how do you find the refractive index of glass using a glass block?

A

1) Draw around a rectangular glass block on a piece of paper and direct a ray of light through it at an angle. Trace the incident and emergent rays, remove the block, then draw in the refracted ray between them.
2) You then need to draw in the normal at 90° to the edge of the block, at the point where the ray enters the block.
3) Use a protractor to measure the angle of incidence (i) and the angle of refraction (r), as shown. Remember — these are the angles made with the normal.
4) Calculate the refractive index (n) using Snell’s law:

n = sin i /sin r

5) Et voilà — you should have found the refractive index of the block.

.

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7
Q

how do you use semicircular block to show total internal reflection

A

1) As you’ve seen, light going from a material with a higher refractive index to a material with a lower refractive index speeds up and bends away from the normal (e.g. when travelling from glass into air).
2) If you keep increasing the angle of incidence (i), the angle of refraction (r) gets closer and closer to 90°.
3) Eventually i reaches a critical angle (C) for which r = 90°. The light is refracted right along the boundary.
4) Above this critical angle, you get total internal reflection — no light leaves the medium.
5) An experiment to demonstrate this uses a semicircular block instead of a rectangular one. The incident light ray is aimed at the curved edge of the block so that it always enters at right angles to the edge. This means it doesn’t bend as it enters the block, only when it leaves from the straight edge.
6) To investigate the critical angle, C, mark the positions of the rays and the block on paper and use a protractor to measure i and r for different angles of incidence. Record your results in a table.

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8
Q
A
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