Question

In the figure shown a converging lens and a diverging lens of focal lengths 20cm and -5cm respectively are separated by a distance such that a paralel beam of light of intensity 100 `watt//m^(2)` incident on the converging lens comes out as parallel beam from the diverging lens. Find the intensity of the outgoing beam in `watt//m^(2)`

A. `400 w//m^(2)`
B. `1200 w//m^(2)`
C. `1600 w//m^(2)`
D. `800 w//m^(2)`

Answer 1

Correct Answer - C

`(I)_("out")=(100(pir_(0)^(2)))/(pi((r_(0))/(4))^(2))=1600 W//m^(2)`