John Henry Poynting

Physicist — John Henry Poynting (Monton, 1852 – Birmingham, 1914) was an English physicist, a pupil of Maxwell at Cambridge and for many years a professor at the University of Birmingham. In 1884 he introduced the concept of energy flux associated with an electromagnetic field, formulating the theorem and vector that bear his name, describing how and in which direction electromagnetic energy propagates through space. This result is essential for understanding the transport of energy by electromagnetic waves, from light to radio waves. Poynting also worked on gravitation, measuring with great care the density of the Earth and the universal gravitational constant. He also studied radiation pressure and the Poynting–Robertson effect on the dynamics of cosmic dust.

Theories and contributions

• Poynting vector — Describes the intensity and direction of electromagnetic energy flux: $\vec{S} = \dfrac{1}{\mu_0}\,\vec{E}\times\vec{B}$.
• Poynting’s theorem — Expresses the conservation of energy in the electromagnetic field, linking the change in energy to the flux of the Poynting vector.

Featured in chapters

19

Linked atoms

2 linked atoms.

19 Le equazioni di Maxwell e le onde elettromagnetiche

• Poynting vector and intensity
• Radiation pressure