JEE MAIN - Physics (2020 - 3rd September Evening Slot - No. 7)
Two light waves having the same wavelength $$\lambda $$ in vacuum are in phase initially. Then the first wave
travels a path L1
through a medium of refractive index n1
while the second wave travels a path of length
L2
through a medium of refractive index n2
. After this the phase difference between the two waves is :
$${{2\pi } \over \lambda }\left( {{n_1}{L_1} - {n_2}{L_2}} \right)$$
$${{2\pi } \over \lambda }\left( {{n_2}{L_1} - {n_1}{L_2}} \right)$$
$${{2\pi } \over \lambda }\left( {{{{L_1}} \over {{n_1}}} - {{{L_2}} \over {{n_2}}}} \right)$$
$${{2\pi } \over \lambda }\left( {{{{L_2}} \over {{n_1}}} - {{{L_1}} \over {{n_2}}}} \right)$$
Explanation
Phase difference = $${{2\pi } \over \lambda }$$ $$ \times $$ optical path difference
= $${{2\pi } \over \lambda }\left( {{n_1}{L_1} - {n_2}{L_2}} \right)$$
= $${{2\pi } \over \lambda }\left( {{n_1}{L_1} - {n_2}{L_2}} \right)$$
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