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 )` can not be equal to `phi_(d)`
B. `phi_(d)` can not 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&d are on the same wavefronts hence `phi_(c ) = phi_(d)` . Similarly point e and f are on the same wavefront hence `phi_(e ) = phi_(f)`. Hence `phi_(d) - phi_(f) = phi_(c ) - phi_(e)`