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 LAWThe magnitude of the induced current depends on four factors:1.The strength of the magnetic field2.The velocity of the magnetic field as it moves past the conductor3.The angle of the conductor to the magnetic field4.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 magnet2. 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 magnet2. Armature (wire loop)3. Source of electrical energy

D/C motor

Induction motor A/C