EMC Question of the Week: June 10, 2019

According to Ampere’s Law, electric currents are always surrounded by

1. electric fields
2. magnetic fields
3. magnetic currents
4. conductors

Answer

The correct answer is "b". The integral form of Ampere’s Law is: ${\displaystyle \oint \overrightarrow{H}\cdot \overrightarrow{d\mathcal{l}}={\displaystyle \underset{S}{\int }\overrightarrow{J}\cdot \overrightarrow{ds}=I_{enclosed}}}$. The left-hand side of this equation expresses the integral of the magnetic field strength around a closed loop. ${\displaystyle \underset{S}{\int }\overrightarrow{J}\cdot \overrightarrow{ds}}$ is the integral of the electric current density over the area enclosed by the loop (i.e. the total current). This current can be a conduction current, J_C, or a displacement current, $\raisebox{1ex}{$\partial \overrightarrow{D}$}\!\left/ \!\raisebox{-1ex}{$\partial t$}\right.$.

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