214 Faraday’s Law Q31.9 As water falls, it gains speed and kinetic energy. It then pushes against turbine blades, transferring its energy to the rotor coils of a large AC generator. The rotor of the generator turns within a strong magnetic field. Because the rotor is spinning, the magnetic flux through its turns changes in time as Φ B BA t = cos ω . Generated in the rotor is an induced emf of ε = − Nd dt B Φ . This induced emf is the voltage driving the current in our electric power lines. Q31.10 Yes. Eddy currents will be induced around the circumference of the copper tube so as to fight the changing magnetic flux by the falling magnet. If a bar magnet is dropped with its north pole downwards, a ring of counterclockwise current will surround its approaching bottom end and a ring of clockwise current will surround the receding south pole at its top end. The magnetic fields created by these loops of current will exert forces on the magnet to slow the fall of the magnet quite significantly. Some of the original gravitational energy of the magnet will appear as internal energy
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .