Download Chapter 20 Electromagnetic Induction

Chapter 20
Electromagnetic Induction
Copyright © 2010 Pearson Education, Inc.
Induced Electromotive Force
Note the motion of the magnet in each image:
Copyright © 2010 Pearson Education, Inc.
(PhET Animations)
Copyright © 2010 Pearson Education, Inc.
Magnetic Flux
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Induced Electromotive Force
Faraday’s experiment: closing the switch in the
primary circuit induces a current in the secondary
circuit, but only while the current in the primary
circuit is changing.
Copyright © 2010 Pearson Education, Inc.
Faraday’s Law of Induction
An emf is induced only when the magnetic flux
through a loop changes with time.
Copyright © 2010 Pearson Education, Inc.
Faraday’s Law of Induction
There are many devices that operate on the basis of
Faraday’s law.
An electric guitar
pickup:
Copyright © 2010 Pearson Education, Inc.
Faraday’s Law of Induction
Microphone:
Copyright © 2010 Pearson Education, Inc.
AC vs. DC
Copyright © 2010 Pearson Education, Inc.
Transformers
A transformer is used to change voltage in an
alternating current from one value to another.
Copyright © 2010 Pearson Education, Inc.
Transformers
By applying Faraday’s law of induction to both coils,
we find:
Here, p stands for the primary coil and
s for the secondary.
Copyright © 2010 Pearson Education, Inc.
Transformers
The power in both circuits must be the same;
therefore, if the voltage is lower, the current
must be higher.
Copyright © 2010 Pearson Education, Inc.
Lenz’s Law
An induced current always flows in a direction
that opposes the change that caused it.
Therefore, if the magnetic field is increasing, the
magnetic field created by the induced current will
be in the opposite direction; if decreasing, it will
be in the same direction.
Copyright © 2010 Pearson Education, Inc.
Lenz’s Law
This conducting rod completes the circuit. As it falls,
the magnetic flux decreases, and a current is
induced.
Copyright © 2010 Pearson Education, Inc.
Lenz’s Law
The force due to the induced current is upward,
slowing the fall.
Copyright © 2010 Pearson Education, Inc.
Lenz’s Law
Currents can also flow in bulk conductors. These
induced currents, called eddy currents, can be
powerful brakes.
Copyright © 2010 Pearson Education, Inc.
Mechanical Work and Electrical Energy
generator demo
Copyright © 2010 Pearson Education, Inc.
Generators and Motors
An electric motor converts electrical energy into
mechanical energy:
Copyright © 2010 Pearson Education, Inc.
Generators and Motors
An electric
generator
converts
mechanical
energy into
electric energy:
Copyright © 2010 Pearson Education, Inc.
Homework
Continue work on fourth quarter project.
First weekly report is due tomorrow.
Copyright © 2010 Pearson Education, Inc.