In the figure light is incident on the thin lens as shown, the radius of curvature for both the surface is R. Determine the focal length of the system.

In the figure light is incident on the thin lens as shown, the radius

1.	In the figure light is incident on the thin lens as shown, the radius of curvature for both the surface is R. Determine the focal length of the system.
Answer» Solution :For refraction at FIRST SURFACE, `mu_2/v_1-mu_1/(-infty)= (mu_2-mu_1)/(+R)….(i)` For refraction at `2^(nd)` surface `mu_3/v_2=mu_2/v_1=(mu_3+mu_2)/(+R)`…….(ii) Adding equations (i) and (ii) we get `mu_3/v_2=(mu_3-mu_1)/R or v_2=(mu_3R)/(mu_3-mu_1)` Therefore focal length of the GIVEN lens system is `(mu_3R)/(mu_3-mu_1)`