Conservation Law

In 1884 English physicist John Henry Poynting (1852-1914) published his theorem, which is an expression of the law of conservation of energy in electrodynamics. We…

We can use Gauss’ law to replace p = Ɛ0 Δ • E in the continuity equation to get Δ. J + [ϐ (Ɛ0 Δ…

Maxwell modified Ampere’s law in 1865 to make it apply to electrodynamics by adding the displacement current to the current. Replacing Ɛ E with D…

Scottish theoretical physicist James Clerk Maxwell (1831-1879) unified electricity and mag-netism into classical electrodynamics. A logical development of his equations follows. In going from electrostatics…

A certain amount of energy is needed to start a current in a circuit – work is done against the back emf to get the…

A changing current not only induces an emf in a nearby circuit, it also induces an emf in the source circuit. As an example, we…

Since electric currents produce magnetic fields, time-varying currents produce time-varying magnetic fields. Hence, a time-varying current in a circuit will produce a time-varying mag-netic flux…

English physicist and chemist Michael Faraday (1791-1867) discovered that the emf produced was proportional to the rate of change of magnetic flux through the circuit.…

The electro motive force (abbreviation emf, symbol Ɛ, unit V) is what drives a current around a circuit. Examples of sources of emf include batteries,…

A magnetic dipole of moment M = mz is located at the origin. A thin circular conducting ring of radius a  vibrates such that the…