SI unit of power of the lens

Q: SI unit of power of lens is?

The reciprocal of a lens’s focal length is its power –

              f = 1/P or P = 1f(m)

Dioptre is the SI unit of power.

The International System of Units (SITU) is a scientific system representing the magnitudes and quantities of significant natural occurrences. 

Power is defined as the quantity of energy transported or converted per unit of time in physics. Also, power is a scalar unit. The motor’s output power is the product of the torque generated by a motor and the angular velocity of its output shaft. 

Similarly, the power dissipated in a circuit’s electrical part is the product of the current running through it and the voltage across it.

A diopter is a unit of magnifying power for a lens or lens system in optics.

The power of a lens in diopters is numerically equal to 1 divided by the focal length in metres because the power of a lens is proportional to unity (one) divided by the focal length.

The magnifying power’s algebraic sign tells whether the lens causes a pencil of parallel light rays to converge or diverge when it is incident.

Thus a diverging lens with a focal length of 1 m has a diopter power of -1, while a converging lens with a focal length of 0.5 m has a diopter power of two. 

The combined power of two or more thin lenses in contact equals the sum of the individual lenses’s powers. For example, combining a -10 diopter lens with a 30 diopter lens yields a converging lens of 20 diopters (of 5 cm focal length).