Question

Which of the following are the possible refractive indices of optical media?

• A. $2.42$
• B. $1.54$
• C. $0.85$
• D. $1.77$

Answer 1

Answer: (A), (B), (D)

The correct options are
A $2.42$
B $1.54$
D $1.77$

The refractive index of a medium is given by the ratio of the speed of light in vacuum ($\text{c}$) to that in the medium ($\text{v}$), i.e. $\frac{\text{c}}{\text{v}}$. For the refractive index to be less than 1, $\frac{\text{c}}{\text{v}}<1⟹\text{c}<\text{v}$.
i.e. there must exist a medium in which the speed of light is greater than that in vacuum, which is impossible, since vacuum is the medium in which light travels the fastest. So, any value of refractive index is possible as long as it is greater than 1.
Therefore, $0.85$ is an impossible and impractical value of refractive index.