Chapter 26: Electromagnetic Induction

Electromagnetic induction describes the generation of an electromotive force or electrical current through the relative motion of a conductor and magnetic field, a principle fundamental to modern electricity generation in applications ranging from bicycle dynamos to large-scale power stations. The chapter establishes that an induced electromotive force arises when magnetic field lines cut through a conductor or when the magnetic flux linking a coil changes over time. Two essential quantities enable calculation and understanding of induction: magnetic flux, defined as the total number of field lines passing through a cross-sectional area and calculated using the equation involving flux density, area, and the angle between the field and the area normal, and magnetic flux linkage, which accounts for multiple turns in a coil by multiplying flux by the number of turns, both measured in webers. The induced electromotive force depends on changes in flux density, the cross-sectional area of the circuit, or the angle between the field and the area. Faraday's law of electromagnetic induction establishes that the magnitude of induced electromotive force is directly proportional to the rate of change of magnetic flux linkage, expressed mathematically with the negative sign representing Lenz's law, which determines that any induced electromotive force opposes the change producing it. Lenz's law reflects energy conservation: the induced current cannot assist the change causing it, as this would create energy from nothing. Instead, mechanical work expended pushing a conductor through a magnetic field converts directly into electrical energy. Determining current direction employs Fleming's right-hand rule for generators, where the thumb represents motion, the first finger indicates the external magnetic field direction, and the second finger shows the induced current direction. Practical applications demonstrate the principle's significance: generators produce electricity by rotating a coil within a magnetic field, with induced electromotive force peaking when the coil aligns parallel to the field and diminishing to zero when perpendicular, while transformers employ a primary coil carrying alternating current to generate changing magnetic flux through a soft iron core, inducing an alternating electromotive force in a secondary coil whose magnitude varies with the turn ratio between coils.