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.

1. In the diagram show the approximate direction of these rays as they emerge out of the block.
2. What is the angle of refraction for the ray PB? 

`("Take" sin 42° =2/3)` 

Answer 1

1. A diagram with rays PA, PB and PC is shown below:
   
2. 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 i_c = 0.667
   i_c = 41.8
   Hence, we can round off i_c = 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°.