Question

what is the focalength of the combination of two thin renses of power -5D and -2D placeci in contact with each other?​

Answer 1

f = - 0.143 m = - 14.3 cm

Step-by-step explanation:

First, we will calculate the power of the combination of lenses:

P = P₁ + P₂

where,

P = Power of Combination = ?

P₁ = Power of first lens = - 5D

P₂ = Power of second lens = - 2D

Therefore,

P = - 5D - 2D

P = - 7D

Now, the focal length can be given as:

`f = (1)/(P) \\\\f = (1)/(-\ 7\ D) \\\\`

f = - 0.143 m = - 14.3 cm

Negative focal length indicates that combination will act as diverging lens.