Fig. shows a surface XY separating two transparent media, medium 1 and medium 2. Lines ab and cd represent wavefronts of a light wave travelling in medium 1 and incident on XY. Line ef and gh represent wavefront of the light wave in medium 2 after rafraciton.

The phase of the ligth wave at c, d, e, and f are `phi_(c)`, phi_(d), `phi_(e)` and `phi_(f)`, respectively. It is given that `phi_(c ) != phi_(f)`. Then

Options

A. `phi_(c)` cannot be equal to `phi_(c)`
B. `phi_(d)` can be equal to `phi_(e)`
C. `(phi_(d)-phi_(f))` is equal to `(phi_(c)-phi_(e))`
D. `(phi_(d)-phi_(c))` is not equal to `(phi_(f)-phi_(e))`

Answer

C

Explanation

Point c and d are on the same wave fronts.
`phi_(C)=phi_(d)`
Also `phi_(c)=phi_(f)` so clearly `phi_(d)-phi_(f)=phi_(c)-phi_(e)`