content(warnings): Add W17-W28, X8-X12, N7 — E&M misconceptions, cross-refs, notes

concepts/em/u13/e13-4-motional-emf.tex

@@ -100,6 +100,8 @@ Thus $P_{\text{mech}} = P_{\text{elec}}$, consistent with conservation of energy
 \]
 This is exactly the motional-emf result $\mathcal{E} = B\ell v$. Faraday's law provides the same emf through the ``flux-change'' perspective, while the motional-emf derivation provides it through the ``force-on-charges'' perspective.}
 
+The motional EMF $\mathcal{E}=B\ell v$ is consistent with Faraday's law $\mathcal{E}=-d\Phi_B/dt$ through the flux change perspective. Both derivations (force-on-charges and flux-change) appear in Sections 13.2 and 13.4 respectively and yield identical results.
+
 \ex{Illustrative example}{A metal rod of length $\ell$ rotates with angular speed $\omega$ about one end in a uniform magnetic field $B$ perpendicular to the plane of rotation. Different points on the rod have different speeds $v(r) = r\,\omega$, so the emf must be computed by integration:
 \[
 \mathcal{E} = \int_{0}^{\ell} B\,(r\omega)\,dr = \frac{1}{2}\,B\,\omega\,\ell^{2}.\]}