Question

Calculate combined focal length of two thin lenses having focal length 12cm and 15cm.​

Answer 1

Explanation:

It depends on type of lenses

For convex lens, focal length is positive

while for concave lens, focal length is negative.

Here lets assume both lenses to be convex.

then

1/f = (1/f1 + 1/f2

= 1/12 + 1/15= 9/60

f = 60/9 = 6 67 cm