A thin film of colorless oil spreads on puddle of

water. Sunlight falls perpendicularly on the film and

reflects into your eyes.

a$)$ What is the phase change upon reflection

from the top surface $($ray$-1)?$ Please explain

your answer calculating the reflection

coefficient of ray$-1.$

b$)$ What is the phase change upon reflection

from the bottom surface $($ray$-2)?$ Please

explain your answer calculating the reflection

coefficient of ray$-2.$

c$)$ If the film eliminates yellow colour of $580$

$mm$ from the reflected light because of

interference between two rays, explain what

type of interference you need and calculate the minimum thickness of the film.

d$)$ If sunlight falls on the film at an angle of $40$ with the surface normal, again calculate the

minimum thickness of the film.