3 ms·
It is inverse square https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/inversesquare.html https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/invers...
by j16sdiz 4y ago
It is inverse square
https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/inversesquare.html https://home.ifa.hawaii.edu/users/barnes/ASTR110L_S03/invers...
- jjtheblunt 4y agothanks for the link. oh, easy way to see it is surface area of a sphere, 4 pi r^2.
- TeMPOraL 4y agoCorrect. The light emitted at a particular point in time forms a section of a spherical surface; as that light travels out, it's like the whole sphere is inflating - the surface area covered by the light remains a fixed fraction of the entire sphere's surface, and so in absolute terms, it grows proportional to r². This means the surface density (light per m²) drops with r². There's probably a nicer way to describe it. If I remember correctly, there's a similar explanation for other phenomena following inverse-square rule, including attraction forces such as gravity, as that r² comes from something forming a surface expanding in space. Inverse cube would give you total energy/power contained in a volume, which isn't usually the interesting quality when talking about radiation. Also, this is why strength of radar return signal drops with fourth power of the distance to target: the illuminating beam drops with 1/r² to target, and then the reflection drops with 1/r² again when traveling back.