Question

A certain region of a soap bubble reflects red light of vacuum wavelength $\lambda =650nm$ . The minimum thickness that this region of soap bubble could have is $13\times {10}^{-x}m$. Find $x$.

( The index of refraction of the soap film is $1.25$)

Answer 1

If $t$ be the thickness of the bubble,
then $4\mu t=\lambda$
Substituting the values,
$t=\frac{6\times {10}^{-9}}{4\times 1.25}$
This gives, $t=13\times {10}^{-8}$
Thus, $x=8$