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. L = 20 cm
B. L = 10 cm
C. L = 40 cm
D. L = 20 / 3 cm

Answer

A

Explanation

`(1)/(f) = (n- 1) ((1)/(R_(1)) - (1)/(R_(2)))`
`rArr (1)/(f) = (1.5 - 1) ((1)/(20) + (1)/(20) ) rArr = 20 cm `
Parallel rays converge at focus.
So, L = f .