Two lenses, one diverging of power 2 dioptre and the other converging of power `6 dioptre` are combined together. Calculate focal length and power of the combination.

Answer

`25 cm, 4D`

Explanation

Here, `P_(1) = - 2D P_(1) = + 6D`
Power of combination,
`P = P_(1) + P_(2) = - 2 + 6 = 4 D`
`F = (100)/(P) = (100)/(4) = 25 cm`