Question

A screen is placed a distance 40 cm away from an illuminated object. A converging lens is palced between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens
A. must be less than 10 cm
B. must be greater than 20 cm
C. must not be greater than 20 cm
D. must not be less then 10 cm

Answer 1

Correct Answer - B
`D=40cm`
For no position of lens `Dlt4f` i.e., `40lt4fimpliesfgt10cm`
The focal length should be greater than 10 cm
out of four options (2) is best option