Phy Chapter 5 Electromagnetic Induction Caltec S.4

ELECTROMAGNETIC INDUCTION This is the effect of producing electric current from magnetism. This principle of electromagnetic induction is demonstrated in the dynamo or electric generators. Faraday’s experiment on electromagnetic induction Ends of cylindrical coil are connected to the galvanometer and then a magnet is plunged into the coil. It is noticed that the galvanometer needle gives momentary deflection showing that a current has been induced in the coil. On removal of the magnet from the coil, the galvanometer gives another deflection but in an opposite direction as shown in the figure below. This effect is called electromagnetic induction. No current (deflection) is induced simply by allowing the magnet to remain at rest inside or outside the coil. Current is induced in the circuit as a result of the wire being cut by magnetic flux (magnetic field lines) when the magnet is removed. Alternatively, we say that the electromotive force is induced whenever there is change in the magnetic flux linked with the coil. Induced current depends on: 1. The number of turns in the coil 2. The strength of the magnet 3. The speed with which the magnet is plunged into the coil. Faraday’s law of electromagnetic induction Whenever there is a change in the magnetic flux linked with a circuit, an electromotive force is induced, the strength of which is proportional to the rate of change of the flux linked with the circuit. Lenz’s law of electromagnetic induction The direction of the induced current is such as to oppose the change producing. Figure above illustrates that application of this law in the case of a magnet plunged into a coil. When the S pole of the magnet is plunged into the coil the induced current must flow in such a direction as to give S polarity to the end …