A pin of length 2.00 cm is placed perpendicular to the principal axis of a converging lens. An inverted image of size 1.00 cm is formed at a distance of 40.0 cm from the pin. Find the focal length of the lens and its distance from the pin.

Answer

B, C

Explanation

Given `h_0=2cm, h_1=-2`
`h_i/h_0v/u, (-2)/2=(-v)/u`
`u=2v`
Also gives,
`v+u=40 cm, 3v=40 cm`
v=13.3=40/3cm, u=80/3`
`1/v-1/u=1/f
`3/40-3/(-80)=1/f`
`rarr 1/f=3/40[1+1/2]=3/40xx3/2`
`f=80/9=8.9cm`
`f=8.9cm, u=26.66cm`