What is the power of a concave lens of focal length `25 cm` ?

The power of a concave lens of focal length 50 cm is :

What do you mean by power of a lens ? What is the SI unit of the power of a lens ? Calculate the power of a concave lens of focal length 25 cm.

The power of a convex lens of focal length 25 cm is …………… .

Calculate the power of a lens of focal length 25 cm .

The power of a concave lens of focal length 20 cm in dioptre is ___________ (fill in the blank)