Question

The refractive index of the material of crystal is 1.68 and that of castor oil is 1.2. When a ray of light passes from oil to glass, its velocity will change by a factor ______.

विकल्प

• `2/3`

• `3/4`

• `5/6`

• `5/7`

Answer 1

The refractive index of the material of crystal is 1.68 and that of castor oil is 1.2. When a ray of light passes from oil to glass, its velocity will change by a factor `underline(5/7)`.

Explanation:

We know, refractive index of crystal w.r.t. oil,

`mu_"co" = mu_"c"/mu_"o" = "speed of light in oil"/"speed of light in crystal"`

Where, µ_c = absolute refractive index of crystal w.r.t. vacuum.

and µ₀ = absolute refractive index of oil w.r.t. vacuum.

`mu_"co" = 1.68/1.2 = 7/5 = "speed in oil"/"speed in crystal"`

Fractional change in velocity,

when light travel from oil to crystal

`= "speed in crystal"/"speed in oil" = 5/7`