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_d`
B. `phi_d`can be equal to `phi_c`
C. `(phi_d-phi_f)` is equal to `(phi_c-phi_c)`
D. `(phi_d-phi_c)` is not equal to `(phi_c-phi_e)`

Answer

C

Explanation

Since points c and d are on the same wavefront, therefore `phi_d=phi_c`
Similarly, `phi_e=phi_f` `:'``phi_d-phi_f=phi_c-phi_f`