Question

A convex lences of focal length 10cm is being placed in contact with concave lence of focal length 20cm what is the focal length of combination

Answer 1

Answer:

focal of convex lens(f)=+20cm=20/100=+.20 m

P=1/f=1/.20=100/20=+5D

focal length of concave lens(f)=-10cm=-10/100=-.1 m

P=1/-.1=-10D

power of combination=5-10=-5D