Lesson 37 Electromagnetic Induction

Electromagnetic induction is the basis for all electrical advancement and electrical discoveries.

Michael Faraday developed the world's first electric motor, where a charged wire follows the circular magnetic field created by the electric current.



Electromagnetic induction is how a magnetic field drives an electric current around a circuit.

Magnetic fields apply forces to electric charges, but only if the charges are in motion.

F=qV x B

The direction of the force is perpendicular to the velocity and the field, and depends on the sign of the charge (negative in this case). Moving a wire charged with electrons through a magnetic field causes the current to flow.

The field of a bar magnet can be perpendicular to every point of a circular loop of wire. Moving the loop drives a current around the loop. Moving the loop up drives the current one way, and moving the loop down drives the current another way. This also applies if the magnet is moved.

Any method of changing magnetic field makes current flow. This causes a change in magnetic flux which changes the current flow as if by voltage. E = d (IO) or Faraday's law. of electro magnetic induction.

Continually rotating a loop of wire in a magnetic field changes the current in the loop. The resulting voltage and current are sinusoidal, going first one way and then the other.

Current flows through a coil of wire when the magnetic flux through it is changing, the current flows one way if the flux decreases and the other way when the flux increases. The current induced in the wire creates a flux of its own, whose direction depends on the dircetion of the current. The flux created by the induced current always opposes a change in the external flux. This is known as Lenz'z law.

An electric current in any circuit creates a magnetic field which whenever it changes induces a current in the same circuit that opposes changes. This is called self-induction.

The induction of a circuit element:

E = -L dI/dt L= (dIO)/dI

Both resstors and capacitor exhibit self-induction. Electric fields will only circulate if magnetic flux is changed.

E = Ointegral(E dr) = -d/dt integral(integral(B dA))