1. The problem statement, all variables and given/known data A narrow beam of light passes through a slab obliquely and is then received by an eye. The index of refraction of the material in the slab fluctuates slowly with time. How will it appear to the eye? 2. Relevant equations 3. The attempt at a solution Let a point object be kept at a distance u to the left of the slab. Now I can find the final position of the image and it comes out to be (t/μ + 1) where t and μ are thickness and refractive index of the slab. Differentiating this wrt time dv/dt = c (dμ/dt) How to interpret this physically?