Power of Lens:The inverse of the focal length is known as the power of the lens.
It shows the bending strength for the light ray of the lens.
The unit of power of a lens is Dioptre when the focal length of the lens is taken in meter (m).
P=
1
f(m)
=
100
f(cm)
where P is the power of the lens and f is the focal length of the lens. EXPLANATION: ●From the above, it is clear that the unit of power of a lens is Dioptre. Therefore option 3 is correct. NOTE:
Concave lens: It is a diverging lens that diverges the parallel beam of light.
It can also gather light from all directions and project it as a parallel beam.
The focal length of the concave lens is negative
It has a virtual focus from the diverging rays of light that seem to converge.
Convex lens : The lens whose refracting surface is upside is called a convex lens