The SI unit of power of lens is :

Question

Accepted Answer

The SI unit of power of a lens is the dioptre, which is represented by Option 4. The power of a lens is defined as the reciprocal of its focal length in meters. It is a measure of how strongly the lens converges or diverges light. The unit dioptre (D) is used to express this power, where 1 dioptre is equivalent to a lens with a focal length of 1 meter. Therefore, a lens with a power of 2 dioptres has a focal length of 0.5 meters.

Now, let's examine why the other options are incorrect:

1. Hertz: Hertz (Hz) is the SI unit of frequency, not the power of a lens. It measures the number of cycles per second of a periodic phenomenon, such as sound waves or electromagnetic waves. Therefore, it is not related to the power of a lens.

2. Lumen: Lumen (lm) is the SI unit of luminous flux, which measures the total quantity of visible light emitted by a source. It is used in the context of lighting and illumination, not in optics for measuring the power of a lens.

3. Ohm: Ohm (Ω) is the SI unit of electrical resistance. It quantifies how strongly a material opposes the flow of electric current. This unit is used in the field of electricity and electronics, not in optics for lens power.

In conclusion, the correct and appropriate unit for measuring the power of a lens is the dioptre, making Option 4 the correct choice.