Question

A glass slab of thickness $4$ cm contains the same numbers of waves as $5$ cm of water when both are traversed by the same monochromatic ray of light. The refractive index of water is $\frac{4}{3}$, what is that for glass?

• A. $\frac{5}{3}$
• B. $\frac{5}{4}$
• C. $\frac{16}{15}$
• D. $\frac{3}{2}$

Answer 1

The correct option is A $\frac{5}{3}$

Given : Thickness of glass-slab $t_g=4cm$

Thickness of water medium $t_w=5cm$

Refractive index of water $n_w=\frac{4}{3}$

Optical path travelled by the wave must be same in both medium as it is given that the number of waves is same in both the medium.

$⟹$ $n_w{t}_w=n_g{t}_g$

$\therefore$ $\frac{4}{3}\times 5=n_g\times 4$ $⟹n_g=\frac{5}{3}$