Mutual inductance
= Mutual inductance
{title2=$M$}
For two fixed linear coils, <mutual inductance> $M$ relates <magnetic flux linkage> in one coil to <electric current> in the other: $\Lambda_{21}=MI_1$. The induced <electromotive force> is $\mathcal E_2=-M\,dI_1/dt$ with consistent winding orientations. For reciprocal coils, $|M|=k\sqrt{L_1L_2}$, where $L_1,L_2$ are <self-inductances> and $0\le k\le1$ measures magnetic coupling. Its <SI> unit is the <henry (unit)>.