Poynting's theorem

Poynting's theorem describes how electromagnetic energy moves and changes within a space. It states that the rate at which energy flows through a surface (called the Poynting vector) plus the energy stored in the electric and magnetic fields equals the rate at which energy is received or lost in a volume, often due to currents or charges. Essentially, it accounts for how electromagnetic energy is transferred, stored, and converted in systems like electrical circuits or antennas, ensuring energy conservation in electromagnetic phenomena.