# What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

#### Focal length of convex lenses, f1=30cm

Focal length of concave lenses, f2=−20cm

⇒1f=1f1+1f2

f=−60cm. Therefore diverging lens .