Transcript Electromagnetic Induction

Electromagnetic
Induction
Chapter 37
Electromagnetic Induction
► Both
Michael Faraday (England) and Joseph Henry
(U.S.) discovered that electric current could be
produced in a wire by simply moving a magnet in
or out of a wire coil
► The production of voltage depends only on the
relative motion of the conductor with respect to
the magnetic field
► The amount of voltage depends on how quickly
the magnetic field lines are traversed by the wire
► Electromagnetic Induction – the phenomenon
of inducing a voltage in a conductor by changing
the magnetic field near the conductor
Electromagnetic Induction
Faraday’s Law
The induced voltage in a coil is proportional to
the product of the number of loops and the
rate at which the magnetic field changes
within those loops.
► The
amount of current produced by
electromagnetic induction depends not only
on the induced voltage but also on the
resistance of the coil and the circuit to
which it is connected
Faraday’s Law
Generators and Alternating Current
► If
one end of a magnet is plunged in and
out of a coil of wire, the induced voltage
alternates in direction
► The frequency of the induced alternating
voltage equals the frequency of the
changing magnetic field within the loop
► Generator – a machine that produces
electric current by rotating a coil within a
stationary magnetic field
► Most commercial generators are run by
moving steam
Generators and Alternating Current
► When
Transformers
you have a pair of coils next to each other, you
will have current passing through both when the
power source is connected
► We refer to the coil connected to the power source as
the primary (input) and the other as the secondary
(output)
► The magnetic field builds up around the primary and
extends into the secondary
► When an iron core inside the coils, the magnetic field
will be intensified
► Transformer – a device for increasing or decreasing
voltage through electromagnetic induction
Primary voltage/# of primary turns =
secondary voltage/#secondary turns
Power into primary = power out of secondary
(voltage x current) primary = (voltage x current) secondary
Transformers
Power Transmission
Induction of Electric and Magnetic
Fields
Faraday’s Law states:
An electric field is created in any region of space in
which a magnetic field is changing with time. The
magnitude of the created electric field is proportional
to the rate at which the magnetic field changes. The
direction of the created electric field is at right angles
to the changing magnetic field.
The companion law is from James Maxwell, it states:
A magnetic field is created in any region of space in
which an electric field is changing with time. The
magnitude of the created magnetic field is
proportional to the rate at which the electric field
changes. The direction of the created magnetic field
is at right angles to the changing electric field.
Electromagnetic Waves
► An
electromagnetic wave is composed of vibrating
electric and magnetic fields that regenerate each
other
► The vibrating fields emanate from the vibrating
charge
► At any point on the wave, the electric field is
perpendicular to the magnetic field, and both are
perpendicular to the direction of motion of the
wave
► Electromagnetic waves always move at the speed
of light (3.0 x 108 m/s), no matter what the
frequency or wavelength or intensity of radiation
Electromagnetic Waves
Homework Assignment (Due 5/5)
► Read
Chapter 37 (pg. 577-591)
► Do Chapter 37 #23-42 (pg. 593-594)
► Do Appendix F, Chapter 37 #1-5 (pg. 691)