The Spark Herald: Electromagnetism / Lightning Command
Electromagnetism & Plasma arc, page 75 of 193. Back to The Pixelated Physics Universe
Who they are
Energy reaches your lamp through the space around the wire, not inside it. Maxwell’s equations predict light, and Poynting showed in 1884 that energy flows where electric and magnetic fields cross. Electrons in a copper wire drift slower than a snail; the lamp lights at once because the field moves at nearly light speed. The Spark Herald on a pixel-art unisex tee; equation, symbols and sources in the panel below.
The Spark Herald is a character of the Electromagnetism & Plasma arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Maxwell's four equations describe every classical electric and magnetic effect: charges make electric fields, there are no magnetic charges, and changing fields create each other. Together they predict electromagnetic waves travelling at the speed of light.
$$ \begin{gathered} \nabla\cdot\vec E = \frac{\rho}{\varepsilon_0} \\ \nabla\cdot\vec B = 0 \\ \nabla\times\vec E = -\frac{\partial\vec B}{\partial t} \\ \nabla\times\vec B = \mu_0\vec J + \mu_0\varepsilon_0\frac{\partial\vec E}{\partial t} \\ c = \frac{1}{\sqrt{\mu_0\varepsilon_0}} \\ \vec S = \frac{1}{\mu_0}\,\vec E\times\vec B \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $\vec E$ | electric field | V/m |
| $\vec B$ | magnetic flux density | T |
| $\rho$ | charge density | C/m³ |
| $\vec J$ | current density | A/m² |
| $\varepsilon_0$ | vacuum permittivity | F/m |
| $\mu_0$ | vacuum permeability | N/A² |
| $c$ | speed of light | m/s |
| $\vec S$ | Poynting vector (electromagnetic energy flux) | W/m² |
Sources
- Maxwell (1865) A dynamical theory of the electromagnetic field, Phil. Trans. R. Soc. 155, 459
- Feynman Lectures on Physics Vol. II Ch. 18: The Maxwell Equations
- Encyclopaedia Britannica — Maxwell’s equations
- NIST CODATA 2022 — vacuum electric permittivity ε0
- NIST CODATA 2022 — vacuum magnetic permeability μ0
- NIST CODATA 2022 — speed of light in vacuum c
- Feynman Lectures on Physics Vol. II Ch. 27: Field Energy and Field Momentum
Crossovers
The Spark Herald meets Homopole (Faraday Paradox). The Spark Herald's energy flows through the fields around a wire, along the Poynting vector. Homopole's spinning copper disk makes an EMF from motion in a magnetic field. In both, the circuit's energy is carried by electric and magnetic fields together.
The Spark Herald meets Recoila (Abraham–Lorentz Force). The Spark Herald's Poynting flux carries energy away from every accelerating charge. Recoila feels the other side of that bill: the radiation reaction force, which takes back energy and momentum from the charge that radiated.
The Spark Herald meets Axona (Hodgkin–Huxley Spike). Axona models a nerve as a circuit: membrane capacitance in parallel with ion conductances. The Spark Herald's Maxwell equations govern every current in it.
Wear the lore
- The Spark Herald – Electromagnetism / Lightning Command Physics T-Shirt
- Related infographic poster: The Poynting Flow – Plate 019 Physics Poster
Concept keywords: Electromagnetism / Lightning Command, The Spark Herald, Electromagnetism & Plasma, physics lore, Pixelated Physics