EMC Question of the Week: August 3, 2026
A 10-volt DC voltage source is connected to a 10-Ω resistor through parallel wires that are each 1 meter long. The current on one of the wires is measured and found to be 1 Ampere. This measurement quantifies
- the flow of electrons in the wire
- the propagation of electromagnetic waves
- ∇×H in the space between the wires
- all of the above
Answer
The best answer is “a.” The conduction current in a wire is dQ/dt, the rate at which electric charge passes through a given location along the wire. The charge moving in a metal wire is in the form of flowing electrons.
A DC circuit has electric and magnetic fields, but it does not generate electromagnetic waves. And even if this circuit had been operating at a high frequency (where the power flow could be quantified in terms of forward and backward propagating waves), the 1 Ampere would be a measurement of the conduction current (the flow of electrons in the wire).
According to Ampere's law, ∇×H is the sum of the conduction and displacement current densities at a point in space. For this DC example, at any point within the wire, it is equal to the total current divided by the cross-sectional area of the wire. At any point in the space between the wires, it is zero.
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