Question

Why is refractive index in a transparent medium greater than one?

• A. Because the speed of light in vacuum is always less than speed in a transparent medium
• B. Because the speed of light in vacuum is always greater than speed in a transparent medium
• C. Frequency of wave changes when it crosses medium
• D. None of these

Answer 1

Answer: (B)

Because the speed of light in vacuum is always greater than speed in a transparent medium

${\left\{\mu v\right\}}_{vacuum}={\left\{\mu v\right\}}_{medium}$

$\Rightarrow {\mu }_{medium}=\frac{speedoflightinvacuum}{speedoflightingivenmedium}$

Here refractive index of medium is inversely proportional to speed of light in the medium. As refractive index of vacuum is 1, speed of light is always greater in vacuum as compared to transparent medium. Hence, refractive index of transparent medium is always greater than one.