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Unit 14
Magnetic Induction
Unit 14 Magnetic Induction
• Discuss magnetic induction.
• List factors that determine the amount and
polarity of an induced voltage.
• Discuss Lenz’s law.
• Review the formula for R-L time constants.
Unit 14 Magnetic Induction
Current flowing out
Current flowing in
Current flowing through a conductor produces
a magnetic field around the conductor.
Unit 14 Magnetic Induction
A voltage is induced when a conductor cuts magnetic lines
of flux.
Unit 14 Magnetic Induction
Reversing the direction of movement reverses the polarity of
the voltage.
Unit 14 Magnetic Induction
Reversing the polarity of the magnetic field reverses the
polarity of the voltage.
Unit 14 Magnetic Induction
Left-hand generator rule.
Unit 14 Magnetic Induction
Voltage is induced by a moving magnetic field.
Unit 14 Magnetic Induction
A single-loop generator.
Unit 14 Magnetic Induction
Increasing the number of turns increases
the induced voltage.
Unit 14 Magnetic Induction
Lenz’s Law
An induced voltage or current opposes the
motion that causes it.
Please note:
Inductors always oppose a change of current!
Unit 14 Magnetic Induction
Inductance is
determined by
the physical
construction of
the coil.
Unit 14 Magnetic Induction
R-L Time Constants
T = time in seconds
L = inductance in henrys
R = resistance in ohms
This formula describes the time necessary for
current in an inductor to reach its full Ohm’s
law value.
Unit 14 Magnetic Induction
1. When current flows, a magnetic field is
created around the conductor.
2. When a conductor is cut by a magnetic
field, a voltage is induced in the
3. The polarity of the induced voltage is
determined by the polarity of the
magnetic field.
Unit 14 Magnetic Induction
4. Three factors that determine the amount
of induced voltage are:
a. the number of turns of wire.
b. the strength of the magnetic field.
c. the speed of the magnetic flux cutting
Unit 14 Magnetic Induction
5. Induced voltage is always opposite in
polarity to the applied voltage.
6. Inductors oppose a change of current.
7. Inductance is measured in units called
henrys (H).
8. Iron core inductors are wound on cores
of magnetic material.