EMC Question of the Week: August 11, 2025

Which of the following is NOT one of Maxwell's equations?  

1. Ohm's Law
2. Gauss's Law
3. Ampere's Law
4. Faraday's Law

Answer

The best answer is “a.” Ohm's law is an equation from circuit theory. It's field-theory equivalent would be  $\overrightarrow{J}=\sigma \overrightarrow{E}$ .

Gauss's Law, Ampere's Law and Faraday's Law are three of Maxwell's equations. The fourth equation, which is often referred to as Gauss's Law for Magnetism, is identical to Gauss's Law with the symbol for magnetic flux replacing the symbol for electric flux and the enclosed charge set to zero.

Two important circuit theory equations can be derived from Gauss's Law and Faraday's Law. Kirchoff's Voltage Law is essentially a statement of Faraday's Law assuming the time-varying magnetic flux passing through the circuit is zero (or negligible). Kirchoff's Current Law is derived by taking the time derivative of Gauss's Law and assuming the displacement current (derivative of the electric flux density) is zero or negligible. In this case, the equation simply states that the net current flowing into a point in space is always zero.

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