Physics

Problem

A coil’s area is slowly increased while the magnetic field passing through it decreases in such a way that the product

BA\cos\theta

remains exactly constant in time. What is the induced emf in the coil at that instant? a)

\displaystyle \mathcal E = B\,\dfrac{dA}{dt}

\displaystyle \mathcal E = B\,\dfrac{dA}{dt}+A\,\dfrac{dB}{dt}

0\,\text{(zero)}

\displaystyle \mathcal E = A\,\dfrac{dB}{dt}