The phenomenon of induction electromotive force caused by the change of magnetic flux, when a part of the conductor in the closed circuit is moving in the magnetic field to cut the magnetic line, the current is produced in the conductor. This phenomenon is called the electromagnetic induction phenomenon. The physics textbook in junior high school can not generalize the electromagnetic induction in an all-round way for the students to understand the electromagnetic induction. Image: the area of the closed coil is unchanged, changing the intensity of the magnetic field, the magnetic flux will also change, and electromagnetic induction will also occur. So the exact definition is as follows: the induced electromotive force due to the change of magnetic flux.
The direction of the electromotive force (minus sign in the formula) is provided by Lenz's law. Lenz's law points out that the magnetic field of the induced current should hinder the change of the original magnetic flux. For the motional electromotive force, the direction of the induced current can be judged by the right hand rule, and the direction of the induced electromotive force can be judged. The meaning of "flux through the circuit" is explained by the following example.
Traditionally, there are two ways to change the flux through the circuit. As for the induced electromotive force, it changes its own magnetic field, such as changing the electric current of the generating field (like a transformer). As for the motional electromotive force, the movement of the whole or part of the circuit in the magnetic field is changed, for example, in a homopolar generator.
The magnitude of the induced electromotive force is determined by Faraday's law of electromagnetic induction; E (T) = -n (d) / (DT). The situation of dynamic life can also be obtained by E=BLV.