PHYSICAL SCIENCE

Magnetism

Part 3: Electric Currents From Magnetism

14.3 Electric Currents From Magnetism Objectives

• Describe the conditions required for electromagnetic induction.

• Apply the concept of electromagnetic induction to generators.

• Explain how transformers increase or decrease voltage across power lines.

Electromagnetic Induction and Faraday’s Law

• Moving a magnet in and out of a coil of wire causes charges in the wire to move.

• Electromagnetic induction is the production of a current in a conducting circuit by a change in the strength, position, or orientation of an external magnetic field.

Faraday’s Law

• Faraday’s Law states: An electric current can be produced in a circuit by a changing magnetic field.

• Michael Faraday (1791-1867) was a British physicist and chemist best know for his law of electromagnetic induction and electrolysis.

Electromagnetic Induction and Faraday’s Law

• As long as a loop of wire continues to move in or out of the field in a direction that is not parallel to the field, an induced current will exist in the circuit.

• An outside force must be used to push the circuit through a magnetic field.

• The stronger the magnetic field, the more energy is required to push the circuit through it.

Electromagnetic Induction

Electromagnetic Induction and Faraday’s Law

• The force of the charge is at its maximum when the charge moves perpendicular to the magnetic field and decreases as the angle between the charge and the magnetic field decreases.

Electromagnetic Induction and Faraday’s Law

• A generator is a device that uses electromagnetic induction to convert mechanical energy into electrical energy.

• Alternating current (AC) is an electric current that changes direction at regular intervals.

AC Generator

Electromagnetic Induction and Faraday’s Law

• The mechanical energy used in commercial power plants comes from a variety of sources.– Falling water from a dam– Burning of fossil fuels to heat water– Using nuclear fission to heat water– Using solar energy to heat water

• Much of the electrical energy produced by generators is lost to external sources.

Electromagnetic Induction and Faraday’s Law

• Electromagnetic waves are made up of oscillating electric and magnetic fields that are perpendicular to each other regardless of frequency.

• Both the electric and magnetic fields are perpendicular to the direction the wave travels – making them transverse waves.

• Each field regenerates the other, allowing them to travel through empty space.

Electromagnetic Wave

Transformers

• A transformer is a device that can change one alternating-current voltage to a different alternating-current voltage.

• The voltage across the secondary coil is greater than the voltage across the primary coil in a step-up transformer.

• In a step-down transformer, the secondary coil has fewer loops than the primary coil, causing the voltage to be lowered by the transformer.

Transformers

• Step-up transformers are used near power plants to increase the voltage to about 120,000 volts to reduce the energy lost due to the resistance of the transmission wires.

• Step-down transformers are used near homes to reduce the voltage to about 120 volts.

Transformers