Question

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

• A. Phase difference of $3\pi$
• B. Path difference of $\frac{3}{\pi }$
• C. Phase difference of $\frac{5\pi }{2}$
• D. Path difference of $5\pi$

Answer 1

The correct option is D Path difference of $5\pi$

For minimum path difference,

$\Delta x=(2n-1)\frac{\gamma }{2}$

where, $\gamma =wavelength$

For $n=3$

$\Delta x=(2\times 3-1)\frac{\gamma }{2}=\frac{5\gamma }{2}$

Phase difference, $\varphi =\frac{2\pi }{\gamma }\times \Delta x$

$\varphi =\frac{2\pi }{\gamma }\times \frac{5\gamma }{2}=5\pi$

The correct option is D.