Partition noise occurs in amplifying (mostly) solid-state circuits. It is caused when a charged carrier, moving from the source, emitter or cathode, has two distinct paths to choose from when it reaches the charge boundary, such as an electron between the base and collector of an NPN transistor, which both appear equally positive at a point between them. At any point in time, there will be a certain amount of electrons choosing the collector and a certain amount choosing the base of the transistor. The small changes in electrons flowing to the collector slightly change the collector current, which flows through the collector resistor, causing a small amount if noise to be introduced.