Principles of Physics Electromagnetic Induction

Changing magnetic fields can create a voltage (and thus cause current to flow) in a conductor A wire moving perpendicular to a magnetic field will experience an induced voltage

Problem: In order to generate voltage and be useful, a wire must move really fast and continue moving. How can this be done? Move in a straight line… B-field would have to be very long Move back and forth… Energy would be lost when changing direction

Problem: In order to generate voltage and be useful, wire must move really fast and continue moving. How can this be done? Spin a wire loop… Even though the wire loop is in the same place, the amount of magnetic field passing through the loop changes as it spins As the loop spins the current changes direction…it alternates

Generators A device that converts mechanical energy (falling water, steam, hand crank) into electrical energy To make a simple generator, wrap a coil of wire around an iron core, place in a magnetic field, and rotate N S

Generators When coil is perpendicular to field lines - current is high When coil is parallel - current is 0. As coil spins current changes from maximum to zero and back over and over again This is AC current – alternating current V t I t

Transformers When electricity is transmitted, high voltages are used to reduce energy lost to heat Energy created must be stepped up to a high voltage and stepped down to be used. A transformer does this

Transformers Alternating current in the primary coil causes a changing magnetic field which is carried by the core to the second coil, causing a current in the second coil. AC input AC output Primary coil Secondary coil Step Up (Higher Voltage)

Transformers The change in voltage is directly dependent on the ratio of turns in the two coils N = number of turns

Transformers P = rate of energy transferred in a transformer P = IV If the transformer is 100% efficient (no energy lost) then I p V p = I s V s power in power out If not, determine the efficiency using Less energy lost = more efficient