= Electromagnetic braking of a sliding rod
{title2=$\tau=mR/(B^2\ell^2)$}
A conducting rod sliding on rails separated by $\ell$ in a transverse magnetic field has induced current magnitude $B\ell v/R$ when self-inductance is neglected and resistance is $R$. The <Lorentz force> opposes motion with magnitude $B^2\ell^2v/R$, so free motion decays exponentially on the displayed time constant. <Joule heating> integrates to the rod's lost kinetic energy. Current direction follows the <Lenz's law>.
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