1) Two light rays having the same wavelength in vacuum are in phase initially. Then, the first ray travels a path L1 through a medium of refractive index μ1 while the second ray travels a path L2 through a medium of refractive index μ2. The two waves are then combined to observe interference. The phase difference between the two waves is A) 2πλ(L1μ1−L2μ2) B) 2πλ(L2−L1) C) 2πλ(μ2L1−μ1L2) D) 2πλ(μ1L1−μ2L2) Answer: Option DExplanation: First ray optical path= μ1L1 Second ray optical path= μ2L2 So, phase difference △ϕ=2πλ× path difference=2πλ×△x △ϕ=2πλ(μ1L1−μ2L2)