Question

In Youngs double slit experiment, an interference patterns is obtained for $\lambda =6000\mathring{A}$, coming from two coherent sources $S_1$ and $S_2$. At certain point $p$ on the screen third dark fringe is formed. Then , the path difference $S_{1}P-S_{2}P$ in microns is:

• A. $0.75$
• B. $1.5$
• C. $3.0$
• D. $4.5$

Answer 1

The correct option is B $1.5$

It is the case of destructive interference where a dark fringe is formed. So,

$\lambda =6000\dot{A}$

$n=3$

$S_{1}P-S_{2}P=\frac{(2n-1)\lambda }{2}$

$S_{1}P-S_{2}P=\frac{(2\times 3-1)6000}{2}$

$=\frac{5\times 6000}{2}=15000\dot{A}=1.5microns$