ABSTRACT
In 3D, the charged particles are coming from all directions. Consider a charged particle of charge q, mass m, and velocity v, traveling along a straight line without any field of interaction. However, there is some conceptual difference, although the current balance equation is applicable in both cases. In a laboratory setting, one varies the applied potential to a Langmuir probe and measures the resultant currents, whereas in space, the incoming and outgoing currents vary naturally, and one measures the resultant spacecraft potential. If there are more currents coming into or going out of a spacecraft or a spacecraft surface, the charging potential ϕ at equilibrium is governed by the current balance of all currents, according to Kirchhoff's law.
