Question

When two lenses 10 cm and -5cm are placed in contact then find the net power.

Answer 1

In the case of convex lens, When the object is af 2F, then the image also forms at 2F with the following characteristics.

Characteristics of image: Real, inverted, same size as that of object

As image distance is given as 40 cm, it should be equal to 2F.

So, focal length, F = 40 / 2 = 20 cm

Power of the lens: P = 100 / F = 100 / 20 = 5D

​Nature of the lens: Convex