Question

(a) The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is 3.0 10⁸ m s (b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?

Answer 1

The refractive index of glass is 1.5 if the speed of light in a vacuum is 3×108 m/s

Answer 2

{A}

★Given:

Refractive index of glass (μ) = 1.5

v = Velocity of light in a medium

Now, the Refractive index of medium is given as,

μ = Velocity of light in vacuum/ velocity of light in medium

1.5 =3.8m/sec÷v m/sec

v = 2×10⁸m/sec

Speed of light in glass is 2 × 108 m/s.

_________________________

{B}

→Speed of light in glass is dependent on the colour of light as different colours have different wavelengths, thus different velocities.

We know that,

μ = a + (b/λ2)

As the wavelength of violet light is smaller than that of red light,

μv > μr.

We also know that μ = c/v

Or v =c/μ

⇒ vv < vr

Hence velocity of violet light in glass is less than velocity of red light.