A beam of monochromatic light, whose wavelength in free space is , is split into two separate

Question:

A beam of monochromatic light, whose wavelength in free space is λ, is split into two separate beams and each is then passed through identical troughs of water. Show that if the water in one trough is stationary and the water in the other trough is moving with speed υ (<< c) in the direction of the light, the phase difference between the emerging beams is
∆Φ = (2π L/λ) (n2 – 1) (v/c)
where L is the length of the troughs and n is the refractive index of the stationary water. Suggest suitable values for L and υ in an experimental arrangement for verifying this result.