Question

A student when discussing the properties of a medium (except vacuum) writes

Velocity of light in vacuum $=$ Velocity of light in medium

This formula is

• A. Dimensionally correct
• B. Dimensionally incorrect
• C. Numerically incorrect
• D. Both a and c

Answer 1

The correct option is D Both a and c

Velocity of light in Vaccum $=C$

Velocity of light in medium $=c/n$

where $n=$ refractive index of medium.

Velocity has dimension $\left[M^{0}L{T}^{-1}\right]$ both in medium and vaccum.

$\therefore$ $V_{medium}\ne V_{vaccum}$

but $dim.\left(V_{medium}\right)=dim.\left(V_{vaccum}\right)$.