2. The statement that the sum of all currents flowing into a node is zero; conversely, the sum of all currents leaving a node must be zero.
Gustav Kirchhoff (184-1887) was a German physicist noted for his formulation of laws related to the conduction of electricity. He also made major contributions in the study of spectroscopy and advanced research into blackbody radiation (emission of radiant energy which would take place from a blackbody at a fixed temperature).
A blackbody is the theoretical surface that absorbs all radiant energy that falls on it, and radiates electromagnetic energy at all frequencies, from radio waves to gamma rays. Because all visible light falling on such a surface is absorbed without reflection, the surface will appear black as long as its temperature is such that its emission peak is not in the visible portion of the spectrum.