For refraction at a spherical surface, the first focal length f is defined as the value of

Question:

For refraction at a spherical surface, the first focal length f is defined as the value of s corresponding to s' = ?, as shown in Fig. 34.59a. The second focal length f' is defined as the value of s' when s = ?, as shown in Fig. 34.59b.(a) Prove that na/nb = f/f'??.(b) Prove that the general relationship between object and image distance is