Poyntingvektori

The Poynting vector, often denoted by the symbol S, is a fundamental concept in electromagnetism that describes the directional energy flux density of an electromagnetic field. In simpler terms, it tells us the amount of energy flowing per unit area per unit time and the direction of that energy flow. It is a vector quantity, meaning it has both magnitude and direction.

The Poynting vector is defined mathematically as the cross product of the electric field vector (E) and the magnetic field vector (H). The formula is S = E × H. The direction of the Poynting vector is perpendicular to both the electric and magnetic fields, indicating the direction in which the electromagnetic energy is propagating. Its magnitude represents the power transmitted per unit area.

The unit of the Poynting vector in the International System of Units (SI) is watts per square meter (W/m²). This unit reflects its definition as power per unit area. The Poynting vector is crucial for understanding the propagation of electromagnetic waves, such as light and radio waves. It quantifies the energy transfer in these waves and is a key component in the Poynting's theorem, which states that the net flow of energy into a volume is equal to the decrease in energy stored within that volume plus the work done by the fields on the charges within the volume.