What is the SI unit of intensity?

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Detailed Solution

In physics, intensity is power per unit area, so the SI unit is watt per square metre (W·m⁻²).

Intensity measures how much power passes through a given area. It applies to waves like sound and light, radiation, and energy beams. Since power is measured in watts and area in square metres, the correct SI unit is W·m⁻². For sound intensity, W·m⁻² is primary, and the related loudness scale uses decibels for intensity level. For light, do not confuse intensity with luminous intensity, which has the base unit candela and refers to light output in a direction as perceived by the human eye. In exam answers, write “Intensity = Power/Area; unit = W·m⁻².”

Formula

I = P/A, where I is intensity, P is power in watts, and A is area in m².

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