A double convex lens made of glass (μ=1.5) has both radii of curvature of magnitude 20 cm. Incident rays parallel to the axis of the lens will converge at a distance L such that:
When rays incident parallel to lens axis then it will converge at the focus and vice versa F=d,R1=+20cm,R2=–20cm
1f=(μ−1)[1R1−1R2]1L=(1.5−1)[120−1−20]L+20cm