Question

Which of the following is/are correct relations?
I. $n_{21}=\frac{1}{n_{12}}$
II. $n_{32}=n_{31} \times n_{12}$
III. $n_{21}=\frac{n_{1 a}}{n_{2 a}}$
IV. $n_{21}=\frac{n_{2 a}}{n_{1 a}}$

• A. I, II and IV
• B. I, III and IV
• C. II, III and IV
• D. I, II, III and IV

Answer 1

Answer: (A)

If $n_{21}$ is the refractive index of medium $2$ with respect to medium $1$ and $n_{12}$ the refractive index of medium $1$ with respect to medium $2$ , then it should be clear that
$n_{12}=\frac{1}{n_{21}}$
It also follows that if $n_{32}$ is the refractive index of medium $3$ with respect to medium $2$, then $n_{32}=$ $n_{31} \times n_{12}$, where $n_{31}$ is the refractive index of medium III with respect to medium $I$.