Question

The minimum thickness of a soap film needed for constructive interference in reflected light, if the light incident on film is of wavelength $900\text{nm}$ is $x\text{nm}$. Find the value of $x$

Refractive index of film is $1.5$.

Answer 1

Condition for constructive interference,
$2\mu t=(2n+1)\frac{\lambda }{2}$
$\Rightarrow t=\frac{(2n+1)\times 900}{4\times 1.5}$
(for minimum thickness, $n=0$)
$\therefore t=150\text{nm}$