A double convex thin lens made of glass (refractive index `mu = 1.5`) has both radii of curvature of magnitude 20 cm . Incident light rays parallel to the axis of the lens will converge at a distance L such that

Options

A. `d=10`
B. `d=20//3`
C. `d=40`
D. `d=20`

Answer

D

Explanation

Here, f=d, `R_(1)=+20` cm, `R_(2)=-20` cm
`(1)/(f)=(mu-1)[(1)/(R_(1))-(1)/(R_(2))]implies(1)/(d)=(1.5-1)[(1)/(20)-(1)/(20)]`
`(1)/(d)=0.5xx(2)/(20), :.d=20` cm.