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Question
The diagram shows the path of a ray of light through a rectangular glass block placed in a liquid of uniform density.
(a) Does the light speed up or slow down in the glass,
(b) Give the reason for your answer.
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Solution
(a) The speed of light, travelling from liquid to glass, slow down.
(b) Speed in liquids = `"Speed of light of air"/"Refractive index of liquid"=(3xx10^8)/"Refractive index of liquid"`
Speed of light in glass = `"Speed of light in air"/"Refractive index of glass"=(3xx10^8)/"Refractive index of glass"`
Since the refractive index in glass is usually higher than that of liquid, hence the speed of light in glass will be less.
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When light travels from a rarer to a denser medium, its speed ______.
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Fig 4.31 below shows a light ray of single colour incident normally on two prisms A and B. In each case draw the path of the ray of light as it enters and emerges out of the prism. Mark the angle wherever necessary.
While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below:
|
S.NO. |
∠i |
∠r |
∠e |
|
I |
60° |
40° |
61° |
|
II |
50° |
36° |
51° |
|
III |
40° |
28° |
39° |
|
IV |
30° |
20° |
31° |
The correct observations is:
(A) I
(B) II
(C) III
(D) IV
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d) Changing refractive index of gases in the atmosphere.
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Explain briefly what causes the twinkling of stars at night.
