Question

In young's double slit experiment, slits are arranged in such a way that besides central bright fringe, there is only one bright fringe on either side of it. Slit separation d for the given condition cannot be (if $\lambda$ is wavelength of the light used):

• A. $\lambda$
• B. $\lambda /2$
• C. $2\lambda$
• D. $3\lambda /2$

Answer 1

Answer: (C)

$2\lambda$

We have, $dsin\theta =n\lambda$
For the first bright fringe, $n=1$
$⟹sin\theta =\frac{\lambda }{d}\le 1$
$⟹d\ge \lambda$
If $d=2\lambda$, the two maxima will be formed.