Question

A thin film of soap solution of refractive index $\mu$ and thickness t appears shining by a normal reflected light wavelength $\lambda$ then t can be

• A. $\frac{\lambda }{2\mu }$
• B. $\frac{2\lambda }{3\mu }$
• C. $\frac{3\lambda }{8\mu }$
• D. $\frac{6\lambda }{8\mu }$

Answer 1

The correct option is D $\frac{6\lambda }{8\mu }$


Path difference (optical) $\Delta x=2\mu t$

For constructive interference

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

$2\mu t=(2n-1)\frac{\lambda }{2}\Rightarrow t=\frac{(2n-1)\lambda }{4\mu }$