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Waves
Waves

Inverse Square Law (Intensity)

I=P4πr2I = \frac{P}{4\pi r^2}

Intensity from point source decreases as 1/r².

Variables

I
Intensity
At distance r
W/m²
P
Power
Source power
W
r
Distance
From point source
m

Derivation

Power spreads over sphere: I = P/(4πr²).

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Common questions

What is the Inverse Square Law (Intensity) formula?

Inverse Square Law (Intensity) is written I = P/4πr². Intensity from point source decreases as 1/r². It belongs to Waves, under Wave Properties.

What are the units in I = P/4πr²?

In SI units, I is intensity, measured in kg/s³; P is power, measured in kg·m²/s³; r is distance, measured in m.

How is the Inverse Square Law (Intensity) formula derived?

Power spreads over sphere: I = P/(4πr²). The result is I = P/4πr².