Transcript Electromagnetic Induction

Electromagnetic Induction
In this chapter we will explore;
• Describe the law of electromagnetic induction and
use Lenz’s law to predict the direction of induced
current.
• Describe alternating current (AC) and the operation
of an AC generator.
• Describe how transformers step-up and step-down
voltage.
• Describe how generators, transformers, and the
electrical work to provide electricity.
13.1 Electromagnetic Induction
In Chapter 12 we learned that an electric current in a
conductor can produce a magnetic field.
Is the opposite true? Can a magnetic field produce
an electric current? In 1831, British physicist Michael
Faraday proved that it could.
Recall that a constant electric current produces a
magnetic field, so it is reasonable to assume that a
constant magnetic field produces an electric
current…however, it does not.
Faraday discovered that the magnetic field must be
continuously changing in order to produce an
electric current.
13.1 Law of Electromagnetic Induction
Electromagnetic Induction is the production of electric current in a conductor
moving through a magnetic field. Induction implies that one action causes another
action to happen, without direct contact.
Faraday brought a permanent magnet near a conductor and induced a current in
the conductor. Electric current was produced only when the magnet was moving in
the vicinity of the conductor.
The Law of Electromagnetic Induction states any change in the magnetic field in
the region of a conductor induces a voltage in the conductor, causing an induced
electric current in the conductor.
13.1 Faraday’s Ring
Faraday demonstrated electromagnetic induction using a device known as Faraday’s
Ring. Closing the switch in the primary coil causes current to flow through the
primary circuit conductor, producing a magnetic around the primary coil.
As the magnetic field grows around the soft-iron ring from zero to maximum
strength, it induces a voltage and current in the secondary coil, until the magnetic
field becomes stable. Once stable, no current is induced.
When the switch is opened, current stops
flowing in the primary coil, collapsing the
magnetic field from maximum strength to zero;
once again inducing a current in the secondary
coil, however in the opposite direction.
13.1 Factors Affecting EM Induction
Several factors determine the amount of current that can be produced by
electromagnetic induction:
• A coiled conductor has more induced current than a straight conductor.
• The greater the number of loops in a coil, the more electric current can be
induced.
• A higher rate of change of the magnetic field; For a coiled conductor and
permanent magnet, the more quickly you move the magnet into and out of the
coil, the greater the induced current.
• The stronger the inducing magnetic field, the greater the induced current.
13.1 Applications of EM Induction
Induction Cooking
Cooking using an induction stove involves a rapidly
changing magnetic field in the stove element,
which induces an electric current in a metal pot.
The pot heats up due to its internal electrical
resistance. Iron pots work better than aluminum or
copper because of its higher resistance. Glass pots
will not work because they are insulating materials.
Induction cooking is more efficient because there is
a more direct thermal energy transfer to the food.
Cooking surfaces do not get hot, so spilled food will
not burn
13.1 Applications of EM Induction
Metal Detectors
Metal detectors use a coil that produces a rapidly
changing magnetic field. This magnetic field induces a
current in any metal near it.
The induced current induces its own magnetic field which
is read by sensitive measuring instruments.
Metal detectors have many practical uses including:
• Locating buried bombs called land mines
• Security purposes at airports, special events
• Hobbyists searching for valuable buried metals
13.1 Implications of Faraday’s Discovery
The implications of Faraday’s discovery were
extraordinary because electricity was generated for
the first time using only a magnet.
Before Faraday’s experiments, the only way to produce
electrical energy was to use an electric cell or battery.
Batteries were could only operate for a limited
amount of time, were heavy and bulky, and could
only produce a small amount of electric potential.
With Faraday’s discovery, all that was required was a
method to keep a magnet moving continuously in
order to produce electrical energy on a large scale
without the limitations of batteries.
13.1 Homework
Questions # 1-5 p.591