Electromagnetic Induction

Motion of a magnet in a coil or loop creates (induces) voltage If coil is connected to complete circuit, current flows Relative motion is needed—it doesn’t matter which moves, the magnet or the coil Amount of voltage depends on rate of motion and number of loops in coil

Faraday’s Law The induced voltage is proportional to the number of loops times the rate of change of the magnetic field Magnetic field is changed by motion or by changing the strength of the field in an electromagnet

Generators Rotating a coil in a magnetic field will create alternating current As coil rotates, amount of magnetic field enclosed by loop changes, inducing a changing voltage Frequency of alternating current is the same as frequency of rotation of the coil Energy is converted from some mechanical form to electrical

Motors and Generators Both have same parts Motors convert electrical energy to mechanical movement using the magnetic force on a moving charge to move the coil Generators convert mechanical to electrical by using the magnetic force due to the coil movement to move the charges through the wire

Transformers Two coils of wire wound on the same iron core so that changes in the magnetic field of the first coil (primary) induce voltage across the second coil (secondary) If ac flows through primary, ac is induced in secondary Voltage in secondary depends on ratio of turns in primary and secondary

Transformers If secondary has more turns, than transformer is called step-up and voltage is increases If secondary has fewer turns, then is called step-down and voltage is decreased Power is not increased so if voltage is stepped up, current is reduced

Transformer Equations Primary turns=Primary voltage Secondary turnsSecondary voltage (Voltage x current) p = (voltage x current) s

Power Transmission Almost all electrical energy is sold as ac because it is easy to change voltage using transformers High voltage and fairly low currents are used to transmit power over long distances This reduces losses due to heating in the wires Voltage is stepped down to 120 V for homes

Electric and Magnetic Fields Faraday’s law holds even if no conductor is present A changing magnetic field induces an electrical field Maxwell extended Faraday’s idea to say a changing electrical field induces a magnetic field

Electrical and Magnetic Fields Electrical and magnetic fields are perpendicular to each other Magnitude of induced field is proportional to rate of change of the other field Explained operation of electromagnetic waves Speed of light is only speed where induction will continue without energy gain or loss