Question

Two thin lenses having focal length + 20 centimetre and minus 30 centimetre Putin contact that we have a cinematic lens find the focal length is doubled what will be the conversion power is the focal length of 2 lens is made the same

Answer 1

f=+20 cm means it is a convex lens
f=-30 cm means it is a concave lens
p=100/20(cm)
=+5cm
p=100/-30(cm)
=-3.33cm