Chapter 8 Section 3--Magnetism

From Mechanical to Electrical Energy Michael Faraday and Joseph Henry (in US Discovered moving a loop of wire through a magnetic field causes an electric current to flow in the wire Electromagnetic induction: producing a current by moving a loop of wire through a magnetic field (or vice versa)

Generators: Generator: a generator produces electric current by rotating a coil of wire in a magnetic field Most of electricity you use each day is produced by generators using electromagnetic induction

Switching Directions A generator’s coil rotates Current flows through the coil Current flow direction must switch periodically to keep electromagnetic coil turning In US—generators rotate 60 X /sec OR 3,700 rpm’s

Using Electric Generators 1 type of generator—alternator in cars Alternators: provide electrical energy to operate lights, etc. Spark plugs also use electricity to ignite fuel in engine’s cylinders Once car is running, mech. Energy turns coil in alternator

Generating Electricity for your home Your electricity comes from a power plant with huge generators Electromagnets in these generators have coils of wire wrapped around iron cores Turbine—rotating magnets in generators are connected to turbines-wheels that rotate when pushed by water, wind or steam

Direct and Alternating Currents Batteries produce—Direct Current (DC) Flows in one direction through a wire Alternating Current (AC)—reverses the direction of the current flow in a regular way *in US—at rate of 60 cycles/sec

Transformers: Transformer: a device that increases or decreases the voltage of an alternating current Made of two coils of wire called primary and secondary coils

More about transformers: Step-up transforms: if 2ndary coil in a transformer has more turns of wire than the primary coil does—steps up Step-down transformers: a transformer that reduces voltage/the number of turns in the secondary coil is less than the number of turns in the primary coil