Find intensity I₂ = I₁ (r₁ / r₂)² for a point source in free space.
| I₂ | – |
Use this calculator when intensity (or flux) falls with the square of distance from a point source. Double the distance and I falls by four. Light, radio, gravity, and Coulomb’s field all follow this when the source is small and there is no absorbing medium. r is distance from the source, not a diameter.
I₁ = 100 at r₁ = 1 and r₂ = 2 gives I₂ = 25. Distances must be greater than zero. I₁ and I₂ share the same unit; the calculator does not convert lux, W/m², or dB.
I₁: Intensity or flux at r₁. Same units as I₂.
r₁: First distance from the source.
r₂: Second distance from the source.
I₂: Intensity at r₂.
Related calculators