Question

In young's double slit experiment, interference pattern is observed on the screen $L$ distance away from slits, distance between centre of two consecutive bright fringes is $x$ and slits separation is $d$, then the wavelength of light will be –

• A. $\frac{xd}{L}$
• B. $\frac{xL}{d}$
• C. $\frac{Ld}{x}$
• D. $\frac{xd}{L+x}$

Answer 1

The correct option is A $\frac{xd}{L}$

$\because$ fringe width is defined as
$\beta =\frac{\lambda D}{d}$
$\lambda =\frac{\beta d}{D}$
but given $\beta =x,D=L$
$\therefore \lambda =\frac{xd}{L}$