Electromagnetic Induction

Current can be created in a wire by a magnetic field British scientist Michael Faraday and American scientist Joseph Henry discovered independently that when a magnet is moved through a coil of wire a current is produced. British scientist Michael Faraday and American scientist Joseph Henry discovered independently that when a magnet is moved through a coil of wire a current is produced. –Voltage can be produced whether a magnet is moved through a coil of wire or a coil of wire is rotated in the presence of an external magnetic field.

The amount of Voltage produced varies The amount of voltage produced depends on: The amount of voltage produced depends on: –How fast the magnetic field lines are traversed.  The faster the magnet traverses the field lines the more voltage is created in the coils. –The number of coils that cross the field lines.  Twice as many coils of wire creates twice as much voltage. Faraday’s Law Faraday’s Law –The induced voltage in a coil of wire is proportional to the number of coils and the rate in which the magnetic filed changes within those coils of wire.

Applications of Electromagnetic Induction Door Bells Door Bells –When a door bell is pressed it completes a circuit with a changing current and creates a changing magnetic field that induces a current in another circuit. The second circuit becomes magnetic and attracts a metal plunger.

Generators and Alternating Current Generators create electrical energy from mechanical energy by rotating a coil of wire in a stationary magnetic field. Generators create electrical energy from mechanical energy by rotating a coil of wire in a stationary magnetic field. The current created from a generator is alternating current. The current created from a generator is alternating current. –As the loop is rotated the direction and magnitude of the voltage and current changes. –One full rotation is one complete cycle.  In the United States generators complete 60 cycles per second. Generators are usually made of many coils of wires wrapped around a metal core. Generators are usually made of many coils of wires wrapped around a metal core. –Usually some type of fuel is used to create the mechanical energy to turn turbines which rotate the coils in very powerful magnetic fields.

Hydroelectric Power plant

Transformers A device that increases or decreases voltage. A device that increases or decreases voltage. –Step up transformers increases voltage. –Step down transformers decreases voltage. –Iron Core with coils wrapped around each side. –One set of coils are attached to an electrical source These are known as the primary coils (N p ) The other set of coils are attached to a device to be powered These are known as the secondary coils (N s ). –Note the primary and secondary coils are not attached to each other. –Alternating current in the primary coils causes a changing magnetic field in the iron core which easily becomes magnetized and enhances the magnetic field. This induces current in the secondary coils.

Transformers

Step up Transformer

Transformer

Transformer Equations V p N p I s V p N p I s _____ ____ = ____ = ___ _____ ____ = ____ = ___ V s N s I p V p voltage in the primary coil V s voltage in the secondary coil N p Number of loops in the primary coil N s Number of loops in the secondary coil I p Current in the primary coil I s Current in the secondary coil