A ray of monochromatic light travels successively from air into a rectangular glass slab and then into a tank of water that is in contact with the lower face of the slab. The two faces of the glass slab are parallel to each other.
(i) Define absolute refractive index of a medium.
(ii) Define relative refractive index of one medium with respect to another.
(iii) Let the absolute refractive indices of glass and water be ng and nw respectively. If nwg denotes the refractive index of water with respect to glass, derive an expression for the refractive index of water with respect to air in terms of ng and nwg.
(iv) State why the relation obtained in part (iii) does not depend on the angle of incidence as long as the two interfaces are plane and parallel.