Topic: Electromagnetics
The Maxwell's equation $\nabla\times\overline{E}=-\frac{\partial\overline{B}}{\partial t}$ is obtained from
- A. Ampere's Law
- B. Faraday's Law
- C. Lenz's Law
- D. Both (b) and (c)
Answer: D. Both (b) and (c)
Explanation: Faraday discovered that the induced emf in a closed circuit is equal to the time rate of change of the magnetic flux linkage. $V_{emf} = -\frac{\partial\psi}{\partial t}$. The negative sign shows that the induced voltage acts in such a way to oppose the flux producing it, as given by Lenz's law. This gives the differential form $\nabla\times\vec{E}=-\frac{\partial\vec{B}}{\partial t}$.