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Transcript
Unit 5 Day 2: Induced EMF in a Moving Conductor • Induced EMF in a Moving Conductor in a Magnetic Field • Force Required to Move a Moving Conductor in a Uniform Magnetic Field • Electric Generators (AC) Induced EMF in a Moving Conductor in a Magnetic Field • The B-Field is out of the paper and perpendicular to a Ushaped conductor with a movable rod, moving at velocity v. The area of the loop increases as it travels to the right d B From Faraday ' s Law :| dt dA B dt l dx B dt dx Blv • This equation is valid if B, l, v are mutually perpendicular. This EMF is called motional EMF Induced EMF in a Moving Conductor in a Magnetic Field • The magnetic force on the electrons on the rod is given by: F qv B where q is the charge on the rod • When the rod moves to the right with velocity v, electrons in the rod also move with this speed & feel the force • Another approach to calculating the EMF, is to determine the work done to move a charge q, from one end of the rod to the other: W F d qvB l The EMF is U W vBl q q The Force Required to Move a Conducting Rod in a Uniform Magnetic Field • To make the rod move to the right an external force must be applied in the direction of motion 2 2 Fext B l v R • The power delivered to move the rod equal the power dissipated in the resistance of the rod. Pext Pdisp v Bl I R R R 2 2 2 2 Electric Generators (AC) • A mechanically turned armature, consisting of N-loops of a coil wound on the armature • As the armature is rotated, an EMF is induced in the rotating coil, which alternates as the magnetic flux through the loop reverses. The induced EMF is: NBA sin t or 0 sin t where 0 NBA Electric Generators (AC) • The induced EMF is a sinusoidal voltage • A typical AC Generator (Alternator):