Transcript Electromagnetism

Electromagnetism
Electromagnetism
• The branch of physics that deals with the
relationship between magnetism and
electricity.
A charge at rest produces no magnetic field. Electrons that flow
through a wire produce a magnetic field about that wire. The
magnetic field is represented by imaginary lines that form
concentric circles centered on the wire
These same rules apply if the current is in a loop. Magnetic field lines form concentric
circles around each tiny section of the wire. Because the wire is curved, however,
these magnetic field lines overlap inside the loop. In particular, at the very center of
the loop, all the field lines come together, making the magnetic field strong
Stacking more loops on top of each other increases the intensity of the magnetic field
running through the center or axis of the stack of loops. The magnetic field of a
solenoid is concentrated through the center of the coil. A coil of wire is called a
solenoid.
The magnetic field can be intensified further by wrapping the coil of wire around
ferromagnetic material, such as iron. The iron core intensifies the magnetic field. In this
case, almost all of the magnetic field lines are concentrated inside the iron core, escaping
only near the ends of the coil. This type of device is called an electromagnet.
An electromagnet is a current-carrying coil of wire wrapped around an iron core, which
intensifies the induced magnetic field.
The magnetic field produced by an electromagnet is the same as that produced by a
bar magnet. That is, if both were hidden from view behind a piece of paper, the
pattern of magnetic field lines revealed by iron filings sprinkled on the paper surface
would be the same. Of course, the advantage of the electromagnet is that its
magnetic field can be adjusted or turned on and off simply by varying the current
through its coil of wire.
Can magnetic fields somehow be used to generate electricity? Michael Faraday, a
self-educated British experimenter, found the answer to that question.
Electromagnetic induction: An electric current is induced in a circuit if some part
of that circuit is in a changing magnetic field.
FARADAY'S LAW
The magnitude of the induced current depends on four factors:
1.The strength of the magnetic field
2.The velocity of the magnetic field as it moves past the conductor
3.The angle of the conductor to the magnetic field
4.The number of turns in the conductor
Actually, no physical motion is needed. An electromagnet can be fixed near a coil of
wire. If the current in the electromagnet is then increased or decreased, its
magnetic field will likewise change and induce a current in the coil.
ELECTRIC GENERATOR
( Dynamo)—A device that converts mechanical energy to
electrical energy by electromagnetic induction.
Generator components:
1. Powerful magnet
2. Armature (wire loop)
A/C generator
D/C generator
ELECTRIC MOTOR-A device that converts electrical energy to
mechanical energy by electromagnetic induction.
Generator components:
1. Powerful magnet
2. Armature (wire loop)
3. Source of electrical energy
D/C motor
Induction motor A/C