20-3-electromagnetic-induction_summary

This section is about electromagnetic induction, which is the process of generating currents with magnetic fields. In 1831, English scientist Michael Faraday and American scientist Joseph Henry independently demonstrated that changing magnetic fields can produce currents. The basic process of generating currents with magnetic fields is called induction, also known as magnetic induction. One way to demonstrate magnetic induction is by moving a bar magnet through a wire coil, with the resulting current measured through the wire. This experiment shows that current is induced only when the magnet moves with respect to the coil, and the current flows in a direction that creates a magnetic field that tends to keep the flux constant in the loop. Faraday reasoned that when a current is induced in the coil, there must be an electromotive force (emf) pushing the charges through the coil. However, the external source doing the work of moving the magnet adds energy to the charges in the coil. The emf is actually a potential and is the energy per unit charge added by a source. The emf produced in a coil due to a moving magnet is proportional to the rate of change of the magnetic field. The mathematical expression for this is: 20.24 where is the change in the magnitude of the magnetic field during time and A is the area of the loop. The induced emf is in the direction that opposes the change in the magnetic flux through the wire loop. This phenomenon is described by Lenz's law. The magnetic flux, represented by , is proportional to the rate of change of the product of the perpendicular magnetic field and the loop area: 20.26 The unit of magnetic flux is the weber (Wb), which is magnetic field per unit area, or T/m2. For a coil made from N loops, the emf is N times stronger than for a single loop.