\mathcal{E} = -\int_{A}^{B} \boldsymbol{E}_\mathrm{cs} \cdot \mathrm{d} \boldsymbol{ \ell } \ , .
In the case of a closed path in the presence of a varying magnetic field, the integral of the electric field around a closed loop may be nonzero; one common application of the concept of emf, known as "induced emf" is the voltage induced in such a loop [REF].