C H A P T E R   22 Electromagnetic Induction

Chapter 22 Electromagnetic Induction Induced emf and Induced current Motional emf Magnetic flux Faraday’s law of electromagnetic induction Lenz’s law Applications: cruise control, ground fault interrupter, induction stove, electric guitar, microphone, & speaker. Electric generator Inductance Transformers and electric power transmission

22.6 Applications of Electromagnetic Induction

The Magnetic Playback Head of a Tape Deck

A Moving Coil Microphone.

22.7 The Electric Generator Electric generators such as these supply electrical power by producing an induced emf according to Faraday's law of electromagnetic induction.

Electric Generator

Emf of the Generator The induced emf is given by the following equation where, N is the number of turns in the coil, B is the magnetic field, A is the area of the coil, and ω is the angular velocity of the rotation of the coil.

Self-inductance (L) The alternating current in the coil generates an alternating magnetic field that induces an emf in the coil. The effect in which a changing current in a circuit induces an emf in the same circuit is referred to as self-induction.

Unit of Inductance The inductance, L is measured in henries. The magnitude of L depends on the geometry of the coil and on the core material. By wrapping the coil around a ferromagnetic (iron) core, the magnetic flux and therefore the inductance can be increased substantially relative to that for an air core. Because of their self-inductance, coils are known as inductors and are widely used in electronics. Inductors come in all sizes, typically in the range between millihenries and microhenries.

22.9 Transformers A transformer is a device for increasing or decreasing an ac voltage. A transformer consists of a primary coil and a secondary coil, both wound on an iron core. The changing magnetic flux produced by the current in the primary coil induces an emf in the secondary coil. At the far right is the symbol for a transformer.

Power Transmission Transformers play a key role in the transmission of electric power.

Transformer A transformer consists of two coils, a primary and a secondary, wound around a soft iron core The two coils are linked by the magnetic field. The soft iron core will provide a medium by which the magnetic flux from the primary coil is transferred to the secondary coil. Transformers are designed so that nearly all the magnetic flux from the primary coil is transferred to the secondary coil.

Transformer Equations Using Faraday’s law we can write expressions for the primary and secondary voltages as follows. Dividing the above equations we get, Assuming that there is no power loss, we can write,

Power Loss in Transmission Lines