Question

In young’s double slit experiment the two slits are 0.6 mm distance apart. Interference pattern is observed on a screen at a distance 80 cm from the slits. The first dark fringe is observed on the screen directly opposite to one of the slits. The wavelength of light will be _____ nm.

Answer 1

$y = \frac d2$

$∴ Δ x = y \frac dD$

$⇒ \frac {d^2}{2D} =\frac λ2$

$⇒ λ = \frac {(0.6 \times 10-3)^2}{0.8}$

$⇒ λ = 450\ \text{nm}$

So, the answer is $450\ \text{nm}$.