15.7: Maxwell's Fourth Equation
( \newcommand{\kernel}{\mathrm{null}\,}\)
This is derived from the laws of electromagnetic induction.
Faraday's and Lenz's laws of electromagnetic induction tell us that the E.M.F. induced in a closed circuit is equal to minus the rate of change of B-flux through the circuit. The E.M.F. around a closed circuit is the line integral of E⋅ds around the circuit, where E is the electric field. The line integral of E around the closed circuit is equal to the surface integral of its curl. The rate of change of B-flux through a circuit is the surface integral of ˙B. Therefore
curlE=−˙B
or, in the nabla notation,
∇×E=−˙B.
This is the fourth of Maxwell's equations.