Question

A thin transparent film with refractive index 1.4 is held on a circular ring of radius 1.8 cm. The fluid in the film evaporates such that transmission through the film at wavelength 560 nm goes to a minimum every 12 seconds. Assuming that the film is flat on its two sides, the rate of evaporation is: 
 

Hint:

For thin film interference, use the relationship between film thickness, wavelength, and time to calculate the rate of evaporation or thickness change.

Answer 1

The rate of evaporation is related to the thickness change that causes a shift in the interference pattern. 
Using the given data and the wavelength for minimum transmission, the rate of evaporation can be calculated as: \[ {Rate of evaporation} = \pi \times 10^{-13} \, {m}^3/{s} \]