2 Chapter 22 Electromagnetic Induction Induced emf and Induced currentMotional emfMagnetic fluxFaraday’s law of electromagnetic inductionLenz’s lawApplications: cruise control, ground fault interrupter, induction stove, electric guitar, microphone, & speaker.Electric generatorInductanceTransformers and electric power transmission
8 Emf of the GeneratorThe 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.
9 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.
10 Unit of InductanceThe 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.
11 22.9 TransformersA 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.
12 Power TransmissionTransformers play a key role in the transmission of electric power.
13 TransformerA transformer consists of two coils, a primary and a secondary, wound around a soft iron coreThe 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.
14 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,