Question

(a) State two laws of refraction of light.
(b) Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is \(3 \times 10^8\) m/s.

Answer 1

(a) Two laws of refraction of light:
1. The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
2. Snell’s Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for the given pair of media.
\[ \frac{\sin i}{\sin r} = \text{constant} = \mu \]

(b) Definition of absolute refractive index:
The absolute refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium.
It is given by the formula:
\[ \mu = \frac{c}{v} \]
where:
μ = absolute refractive index,
c = speed of light in vacuum,
v = speed of light in the medium.

Given:
μ = 1.5
c = \(3 \times 10^8\) m/s

To find: Speed of light in glass (v)
\[ v = \frac{c}{\mu} = \frac{3 \times 10^8}{1.5} = 2 \times 10^8 \, \text{m/s} \]

Final Answer:
Speed of light in glass = 2 × 10⁸ m/s