a screen is placed a distance 40 cm away from an illuminated object.a converging lens is placed 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 lenth of lens.

A)must be less than 10 cm

B)must be gretaer than 20 cm

C)must not be greater than 20cm

​D) must not be less than 20 cm

Give detailed answe

Since image couldn’t be found on the screen, means image formed is farther from the screen. In converging lens, image formed at 2F and within 2F is formed at 2F and beyond 2F respectively. So, the focal length must be greater than 10 cm i.e 2F is 20 cm which means 40 cm is minimum separation between object and image.
None of the above has correct options. Probably B option is misprinted as 20 cm, it should be 10 cm.