Question

$S_1,S_2$ are two coherent sources of light. P is a point on the screen such that $S_{2}P-S_{1}P$ = 0.01029 cm. Wave length of light used is $6000\dot{A}$. The order of the fringe formed at P is

• A. 172, bright
• B. 171, bright
• C. 173, dark
• D. 172, dark

Answer 1

The correct option is D 172, dark

$x=(2n–1)\frac{\lambda }{2}$
$1029\times {10}^{-7}=(2n-1)\frac{6000\times {10}^{-10}}{2}$
$2\times 171.5=2n-1$
$344=2n$
$n=172$