Question

A thin film of oil of thickness t is floating on water. The oil has index of refraction no = 1.4. There is air above the oil. When viewed from the air in the direction normal to the surface, there is constructive interference of reflected red light with lambda = 675 nm. Find the minimum thickness t of the oil film that will give constructive interference of reflected light with lambda = 675 nm.

Answer 1

Answer:t=0.1205

Explanation:

Given

Refractive index of oil$\left ( \mu \right )=1.4$

Wavelength of red light =675 mm

Condition for constructive interference is

$2\mu _{oil}t=\frac{m\lambda }{2}$

$t=\frac{m\lambda }{4\mu _{oil}}$

For m= 1 i.e. for minimum thickness

$t=\frac{1\times 675\times 10^{-9}}{4\times 1.4}$

$t=0.1205 \mu m$