Question

When a convex lens of focal length 30cm is i in contact with a concave lens of focal length 20cm, fimd if the system is converging or diverging?

Answer 1

Solution :

given : f1=30,f2=−20cmf1=30,f2=−20cm

1f=1f1+1f21f=1f1+1f2

=> 1f=130−1201f=130−120

=2−360=2−360

=−160=−160

f=−60cmf=−60cm

The focal length of the combination is −60cm−60cm .

If behaves as a concave lens (ie) it is a diverging lens.