Point source

The actual source need not be physically small if its size is negligible relative to other length scales in the problem.

For example, in astronomy, stars are routinely treated as point sources, even though they are in actuality much larger than the Earth.

Although singularities such as this do not exist in the observable universe, mathematical point sources are often used as approximations to reality in physics and other fields.

Radio emissions generated by a fixed electrical circuit are usually polarized, producing anisotropic radiation.

Examples: A coaxial loudspeaker is designed to work as a point source to allow a wider field for listening.

The most common form of anisotropy is the formation of a thermal plume above the heat source.

Whereas fluid sinks exhibit complex rapidly changing behavior such as is seen in vortices (for example water running into a plug-hole or tornadoes generated at points where air is rising), fluid sources generally produce simple flow patterns, with stationary isotropic point sources generating an expanding sphere of new fluid.

If the fluid is moving (such as wind in air or currents in water) a plume is generated from the point source.