Question

Focused 20 cm from the lens. when a
diverging lens is placed in contact with the
converging lens, the rays are for 30 cm from
the combination. what is the focal length of
the diverging lens.

Answer 1

Answer:

Given, 

Focal length of converging lens, f1=20 cm

Focal length of diverging lens,f2=−5 cm

feq=f1+f2−df1f2

Since there is no deviation, 

feq=∞

⇒f1+f2−d=0

⇒f1+f2=d

20−5=d

⇒d=15 cm