A ray of light is incident on a thin film, As shown in figure, M and N two reflected rays while P and Q are two transmitted rays. Rays N and Q undergo a phase change of `pi`. Correct ordering of the refracting indices is

Options

A. `n_(2) gt n_(3) gt n_(1)`
B. `n_(3) gt n_(2) gt n_(1)`
C. `n_(3) gt n_() gt n_(2)`
D. none of these, the specified changes cannot occur

Answer

b

Explanation

Ray N undergoes reflection at surface II with phase change of `pi`.
`implies n_(3) gt n_(2) `
Ray Q undergoes a phase change of `pi` at surface II, but there is no phase change when it is reflected from surface I.
`implies n_(1) lt n_(2) `