Question

A piece of glass has a thin film of gasoline floating on it. A beam of light is shining perpendicular on the film. If the wavelength of light incident on the film is 560 nm and the indices of refraction of gasoline and glass are 1.40 and 1.50, respectively, what is the thickness of the film if we see a bright reflection in the visible range

Answer 1

Answer:

200 nm

Explanation:

Refractive index of gasoline = 1.4

Wavelength = 560 nm

t = Thickness of film

m = Order = 1

Wavelength is given by

$\lambda=\dfrac{560}{1.4}=400\ nm$

We have the relation

$2t=m\lambda\\\Rightarrow t=\dfrac{m\lambda}{2}\\\Rightarrow t=\dfrac{1\times 400}{2}\\\Rightarrow t=200\ nm$

The thickness of the film is 200 nm