Question

A converging and a diverging lens of equal focal lengths are placed co-axially in contact. Find the power and the focal length of the combination.

Answer 1

If f and -f be the focal length of coverging and diverging lenses respectively, then Power of combination,

P = P₁ + P₂ = \(\frac{1}{f} - \frac{1}{f} = 0\)

∴ Focal length of combination

F = \(\frac{1}{P} = \frac{1}{0} = \infty\)