A thin lens made of a material of refractive index μ2 has a medium of refractive index μ1, on one side and a medium of refractive index μ3, on the other side. The lens is biconvex and the two radii of curvature have equal magnitude R. A beam of light travelling parallel to the principal axis is incident on the lens. Where will the image be formed if the beam is incident from (a) the medium μ1, and (b) from the medium μ3 ?
