Question

2. An object is placed at a distance of 50 cm from a
concave lens. The image is formed at a distance of
20 cm from the lens. Find the focal length of the lens.​

Answer 1

Explanation:

Take -ve sign where the refracted or reflected ray goes

v = 20cm

u = -50cm

f = ?

Lens formula is

1÷f = 1÷v - 1÷u