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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 (17911867) 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