Question

What is the focal length of a concave lens?

Answer 1

Concave lens:

1. A concave lens is a lens that diverges a straight light beam from the source to a diminished, upright, virtual image.
2. It can form both real and virtual images. Concave lenses have at least one surface curved inside.
3. A concave lens is also known as a diverging lens because it is shaped round inwards at the center and bulges outwards through the edges, making the light diverge.

Focal length of a concave lens:

1. The distance between the optical center of the concave lens and the principal focus is called the focal length
2. According to the sign convention, the focal length of a concave lens is always negative.

Hence, the focal length of the concave lens is negative.