Q82 / 90 · JEE Main 2021 (27 Jul Shift 2) · Physics

The difference in the number of waves when yellow light propagates through air and vacuum columns of the same thickness is one. The thickness of the air column is _____ $mm$ . [Refractive index of air $= 1.0003$ , the wavelength of yellow light in vacuum $= 6000 \overset{\circ}{A}]$

Correct answer: 2

Solution

Thickness $t = n λ$

So, $n λ_{vac} = (n + 1) λ_{air}$

$n λ = (n + 1) \frac{λ}{μ_{air}}$

$n = \frac{1}{μ_{air} - 1} = \frac{10^{4}}{3}$

$t = n λ$

$= \frac{10^{4}}{3} \times 6000 \overset{0}{A}$

$= 2 mm$

Hence, the correct answer is 2.