A pickup coil is mounted on the axle support • When the magnet passes over the pickup coil, a pulse is generated • A computer keep tracks of the number of pulses Section 21.7
Ground Fault Interrupters • A ground fault interrupter (GFI) is a safety device used in many household circuits • It uses Faraday’s Law along with an electromechanical relay • The relay uses the current through a coil to exert a force on a magnetic metal bar in a switch Section 21.7
GFI, cont. • During normal operation, there is zero magnetic field in the relay • If the current in the return coil is smaller, a non-zero magnetic field opens the relay switch and the current turns off
Electric Guitars • An electric guitar uses Faraday’s Law to sense the motion of the strings • The metal string passes near a pickup coil wound around a permanent magnet • As the string vibrates, it produces a changing magnetic flux • The resulting emf is sent to an amplifier and the signal can be played through speakers Section 21.7
Generators, Motors and Cars • Motors and generators provide examples of conservation of energy and the conversion of energy from one type to another • A hybrid car contains two motors and a generator • The hybrid car “recaptures” some of the energy normally converted to heat when braking and stores it in batteries • A hybrid car is a practical example of the conversion between mechanical and electrical energy Section 21.7
Induction from a Distance • Assume a very long solenoid is inserted at the center of a single loop of wire • The field from the solenoid at the outer loop is essentially zero Section 21.8
Induction from a Distance, cont. • The field inside the solenoid at the center of the loop still produces a magnetic flux through the inner portion of the loop • Energy is transferred across the empty space between the two conductors • The energy is carried from the solenoid to the outer loop by an electromagnetic wave Section 21.8
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- Magnetic Field