Question

The speed of light in air is 3 x 108 m/s and the speed of light in glass is 2 x 108 m/s. Then what is the reflective index of glass?

Answer 1

refractive index of a medium = speed of light in air/speed of light in the medium
Refractive index of glass = 3 x 108 ms-1/ 2 x 108 ms-1
                                            = 1.5

Answer 2

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Glass refractive index is defined as the ratio between the speed of light in the vacuum and the speed of light in the glass.

Refractive index of glass (ng) = Speed of light in vacuum/speed of light in the glass.

ng = (3 ×108)/ (2 ×108)

ng = 1.5