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Question
The refractive index of glass is 1.5. From a point P inside a glass block, draw rays PA, PB and PC incident on the glass air surface at an angle of incidence 30°, 42° and 60° respectively.
- In the diagram show the approximate direction of these rays as they emerge out of the block.
- What is the angle of refraction for the ray PB?
`("Take" sin 42° =2/3)`
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Solution
- A diagram with rays PA, PB and PC is shown below:
- Given, μ = 1.5
As we know,
`sin i_c = 1/mu`
substituting the values in the formula, we get,
`sin i_c = 1/1.5`
sin ic = 0.667
ic = 41.8
Hence, we can round off ic = 42°
Applying `sin r/sin i = ""_amu_g`
sin r = `""_amu_g xx sin i`
sin r = `""_amu_g xx sin 42°`
Given, sin 42° = `2/3`
and `""_amu_g = 3/2`
substituting the value in the formula, we get,
`sin r = 3/2 xx 2/3`
sin r = 1
As sin r = 1, the angle of refraction is 90°.
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The diagram shows the path of a ray of light through a rectangular glass block placed in a liquid of uniform density.
What should be the rate of the speed of light through the liquid to the speed through the glass so that there is no refraction of light at the boundaries of the glass block when the system is illuminated by the light of one colour?
