Question

8. [1pt] A 29.1cm focal length converging lens is 18.3cm behind a diverging lens. Parallel light strikes the diverging lens. After passing through the converging lens, the light is again parallel. What is the focal length of the diverging lens?

Answer 1

Combined focal length of twolenses separated by a distance 'd'

   1/f   =   1/f1   +   1/f2   -   d/f1*f2

   Since the ray remainsundeviated after passing through both lenses,f   =   ?

   Given      f1   =   29.1 cm,   d   =   18.3 cm

   1/?   =   1/29.1 + 1/ f2   -   18.3 /29.1*f2

   f2   =   -10.8 cm

   -ve sign indicates a diverging lens.