Question

What is the SI unit of power of lens ?

Answer 1

Hint: Learn about different physical quantities and their units. Power of a lens is the ability of the lens to diverge or converge the light. The more the power of a lens the more easily it deviates the incident light.

Formula used:
The power of a lens is given by the inverse of its focal length,
$$P={\displaystyle \frac{1}{f}}$$
where, $$P$$ is the power of the lens and $$f$$ is the focal length of the lens.

Complete step by step answer:
The power of a lens is the measure of is a measure of the amount of deviation of light ray produced by a lens. The more the light bends easily the more is the power of the lens. So, it is the ability of the device to diverge or converge the light easily. If we look into the unit of different units of physical quantities we find that the SI unit of power of lens is dioptre.

The sign of the unit dioptre is $$D$$. The power of a lens is given by the inverse of its focal length, $$P={\displaystyle \frac{1}{f}}$$.For example, $$1D$$ means the focal length of the lens is $$+1m$$. The positive sign implies that the lens is a convex lens.And negative power implies that the lens is a concave one.

Hence, the SI unit of power of the lens is dioptre.

Note: The more the power means the light will converge with in a less area or diverge from a less area. When the light converges or diverges to a single point the intensity of the light becomes maximum. For ideal lens light converges or diverges to a single point hence the maximum intensity but in real life the spread covers a minimum area.