Question

The minimum value of relative refracting index is:

• A. Zero
• B. Less than 1 but not zero
• C. 1
• D. More than 1.

Answer 1

Answer: (B)

Less than 1 but not zero

Answer 2

The refractive index of medium b w.r.t. medium a is given by $\,^an_b=\frac{speed \,of \,light\, in\, a}{speed \,of \,light \,in \,b}$ Since, the speed of light in vacuum is the maximum, therefore, in principle, the refractive index of vacuum w.r.t any other medium is less than 1. However, in general, we define refractive index of different media w.r.t. vacuum and these values are greater than 1. The refractive index w.r.t. vacuum is often called absolute refractive index.