Question

In Young's double slit experiment, when two light waves form third minimum, they have

• A. Phase difference of $3\pi$
• B. Phase difference of $5\pi /2$
• C. Path difference of $3\lambda$
• D. Path difference of $5\lambda /2$

Answer 1

Answer: (D)

For minima, path difference $\Delta =(2n-1)\frac{\lambda }{2}$
For third minima $n=3$
$\Rightarrow \Delta =(2\times 3-1)\frac{\lambda }{2}=\frac{5\lambda }{2}$