Electromagnetic Electromagnetic InductionInduction

Current can be created in a Current can be created in a wire by a magnetic fieldwire by a magnetic field

British scientist Michael Faraday and British scientist Michael Faraday and American scientist Joseph Henry American scientist Joseph Henry discovered independently that when discovered independently that when a magnet is moved through a coil of a magnet is moved through a coil of wire a current is produced.wire a current is produced.– Voltage can be produced whether a Voltage can be produced whether a

magnet is moved through a coil of wire magnet is moved through a coil of wire or a coil of wire is rotated in the or a coil of wire is rotated in the presence of an external magnetic field.presence of an external magnetic field.

The amount of Voltage The amount of Voltage produced variesproduced varies

The amount of voltage produced depends on:The amount of voltage produced depends on:– How fast the magnetic field lines are traversed.How fast the magnetic field lines are traversed.

The faster the magnet traverses the field lines the more The faster the magnet traverses the field lines the more voltage is created in the coils.voltage is created in the coils.

– The number of coils that cross the field lines.The number of coils that cross the field lines. Twice as many coils of wire creates twice as much voltage.Twice as many coils of wire creates twice as much voltage.

Faraday’s LawFaraday’s Law– The induced voltage in a coil of wire is proportional The induced voltage in a coil of wire is proportional

to the number of coils and the rate in which the to the number of coils and the rate in which the magnetic filed changes within those coils of wire.magnetic filed changes within those coils of wire.

Applications of Applications of Electromagnetic InductionElectromagnetic Induction

Door BellsDoor Bells– When a door bell is pressed it When a door bell is pressed it

completes a circuit with a changing completes a circuit with a changing current and creates a changing current and creates a changing magnetic field that induces a current in magnetic field that induces a current in another circuit. The second circuit another circuit. The second circuit becomes magnetic and attracts a metal becomes magnetic and attracts a metal plunger. plunger.

Generators and Alternating Generators and Alternating CurrentCurrent

Generators create electrical energy from Generators create electrical energy from mechanical energy by rotating a coil of wire in a mechanical energy by rotating a coil of wire in a stationary magnetic field.stationary magnetic field.

The current created from a generator is The current created from a generator is alternating current.alternating current.– As the loop is rotated the direction and magnitude of the As the loop is rotated the direction and magnitude of the

voltage and current changes.voltage and current changes.– One full rotation is one complete cycle.One full rotation is one complete cycle.

In the United States generators complete 60 cycles per In the United States generators complete 60 cycles per second.second.

Generators are usually made of many coils of Generators are usually made of many coils of wires wrapped around a metal core.wires wrapped around a metal core.– Usually some type of fuel is used to create the Usually some type of fuel is used to create the

mechanical energy to turn turbines which rotate the mechanical energy to turn turbines which rotate the coils in very powerful magnetic fields.coils in very powerful magnetic fields.

Hydroelectric Power plantHydroelectric Power plant

TransformersTransformers A device that increases or decreases voltage.A device that increases or decreases voltage.

– Step upStep up transformers increases voltage. transformers increases voltage.– Step downStep down transformers decreases voltage. transformers decreases voltage.– Iron Core with coils wrapped around each side.Iron Core with coils wrapped around each side.– One set of coils are attached to an electrical source One set of coils are attached to an electrical source

These are known as the primary coils (NThese are known as the primary coils (Npp) The other set ) The other set of coils are attached to a device to be powered These of coils are attached to a device to be powered These are known as the secondary coils (Nare known as the secondary coils (Nss).).

– Note the primary and secondary coils are not attached Note the primary and secondary coils are not attached to each other.to each other.

– Alternating current in the primary coils causes a Alternating current in the primary coils causes a changing magnetic field in the iron core which easily changing magnetic field in the iron core which easily becomes magnetized and enhances the magnetic field. becomes magnetized and enhances the magnetic field. This induces current in the secondary coils.This induces current in the secondary coils.

TransformersTransformers

Step up TransformerStep up Transformer

TransformerTransformer

Transformer EquationsTransformer Equations

VVpp NNp p IIss

______________ ____ = = ________ = ___= ___

VVss N Nss IIpp

VVpp voltage in the primary coil voltage in the primary coil

VVs s voltage in the secondary coilvoltage in the secondary coil

NNpp Number of loops in the primary coil Number of loops in the primary coil

NNs s Number of loops in the secondary coilNumber of loops in the secondary coil

IIpp Current in the primary coil Current in the primary coil

IIss Current in the secondary coil Current in the secondary coil