The refractive index of glass is 1·5. If the speed of light in air is 3 × 10 ⁸ m/s then its speed in glass will be

CONCEPT:

• Refractive index (μ): The ratio of the speed of light in air to the speed of light in the medium is called the refractive index of that medium.

\(Refractive\; index = \frac{{speed\;of\;light\;in\;air(c)}}{{speed\;of\;light\;in\;medium (v)}} = c/v\)

CALCULATION:

Given that:

Refractive index of glass (μ) = 1.5

Speed of light in air (c) = 3 × 10⁸ m/s

Since μ = c/v

So the speed of light in glass (v) =\(\frac {c}{\mu}= \frac{(3 × 10^8 m/s)}{1.5} = 2 × 10^8 m/s\) 

Hence option 1 is correct.