Question

Two coherent point sources $s_1$and $s_2$emit light of wave length $\lambda$ the separation between then is $2\lambda$The
smallest distance from $s_2$ on the line passing through $s_2$ and perpendicular to $s_1{s}_2$where minimum intensity
occurs is

• A. $\frac{7\lambda }{12}$
• B. $\frac{15\lambda }{4}$
• C. $\frac{\lambda }{2}$
• D. $\frac{3\lambda }{4}$

Answer 1

The correct option is B $\frac{15\lambda }{4}$

$\sqrt{(2\lambda {)}^2+x^2}-x=\frac{\lambda }{2}4{\lambda }^2+x^2=x^2+\frac{{\lambda }^2}{4}+\lambda xx=\frac{15\lambda }{4}$