Question

An oil film (n = 1.48) of thickness 290 nm floating on water is illuminated with white light at normal incidence. What is the wavelength of the dominant color in the reflected light? A. Blue (470 nm) B. Green (541 nm) C. Violet (404 nm) D. Yellow (572 nm)

Answer 1

Answer:

The correct option is  D

Explanation:

From the question we are told that

   The  refractive index of oil film is $k = 1.48$

   The  thickness is $t = 290 \ nm = 290*10^{-9} \ m$

   

Generally for constructive interference

      $2t = [m + \frac{1}{2} ]* \frac{\lambda}{k}$

For reflection of a bright fringe m =  1

 =>   $2 * (290*10^{-9}) = [1 + \frac{1}{2} ]* \frac{\lambda}{1.48}$

=>     $\lambda = 5.723 *10^{-7} \ m$

This wavelength fall in the range of a yellow light