CHAPTER 2

CHAPTER 2BASIC PRINCIPLES OF ELECTROMAGNETISM Learning Outcomesi. Explain relationship between current flow and magnetism

ii. Understand the characteristics of magnetic quantities in electromagnet

Basic Principles Of ElectromagnetismAll materials are made up of atoms. An atom has a nucleus around which one or more electrons circle in different orbits.

An electron has a negative electric charge and a nucleus has a positive one.

Conductor, Insulator and SemiconductorConductorsMaterials in which free electrons can be made to move are known as conductors. Most metals are good conductors. Example iron, aluminum, bronze and steel.

InsulatorsMaterials in which free electrons are not readily movedInsulators are generally non-metallic and include rubber

SemiconductorsSemiconductors are materials whose free electrons ability to move falls between that of conductors and insulators

Direction Of Current FlowBy convention, electric current flows from high potential (+, positive) to low potential (, negative).

R1=15R2=10V=120VThe behavior of magnets and the main rules that concern us are as follows:i. Magnets have north and south poles. ii. Magnets have magnetic fields. iii. Magnetic fields are made up from lines of magnetic force. iv. Magnetic fields flow from north to south.

Magnet

Electricity and MagnetismElectromagnetism is produced when an electrical current flows through a simple conductor such as a piece of wire or cable.

A small magnetic field is created around the conductor with the direction of this magnetic field with regards to its "North" and "South" poles being determined by the direction of the current flowing through the conductor.

Relationship that exists between Electricity and Magnetism in the form of Electromagnetism.current flow in a single conductor When a current flows through a conductor, it produces a magnetic field.

The direction of the current in the conductor is indicated by the symbols which indicates a current flowing away from you, or INTO the plane of the screen, and , which indicates a current moving towards you, or OUT of the screen

Consider a dart, with the current flowing in the direction of its point.Now stick it in a piece of cardboard, and view it from the top. It mimics the current flowing away from the viewer and into the cardboard. Now turn the cardboard over, and look at the point, which symbolizes the current flowing towards the viewer.

If currents pass along two parallel wires, each wire will set up a magnetic field and the fields will interact according to the rules described in the previous topic.

Two parallel conductors which each carry a current in the SAME DIRECTION will ATTRACT one another.

Two such conductors which carry currents in an OPPOSITE DIRECTION will REPEL each other:

current flow in two conductor

factors that affect electromagnetic strength Current StrengthAs current increases, magnetism increase. Current directly proportional to electromagnetic strength.

Conductor lengthAs length increases, magnetism decreases. Length inversely proportional to electromagnetic strength.Coil LengthAs coil length increases, magnetism increases. Coil length directly proportional to electromagnetic strength.

MAGNETISMELECTRICITYELECTROMAGNETISMSINGLE CONDUCTORTWO CONDUCTORFACTORCOIL LENGTHCONDUCTOR LENGTHCURRENT STRENGTHANTICLOCKWISECLOCKWISEATTRACTREPELElectromagnetic InductionBasic laws:A method of obtaining an electric current with the aid of magnetic flux.When a conductor cuts or is cut by magnetic flux, a voltage is generated in the conductor.The magnitude of voltage is proportional to the rate at which the conductor cut or is cut by the magnitude flux(flux meaning something that flows).The direction of the induced voltage depends upon the direction of the magnetic field and the direction in which the field moves relative to the conductor.

Mutual InductionIf two coils (known as the primary and secondary) are wound on to the same iron core then any change in magnetism of one coil will induce a voltage into the other.

This happens when a current to the primary coil is switched on and off.

If the number of turns of wire on the secondary coil is more than the primary, a higher voltage can be produced.

If the number of turns of wire on the secondary coil is less than the primary a lower voltage is obtained. This is called transformer action and is the principle of the ignition coil.

The value of this mutually induced voltage depends on:The primary current.The turns ratio between primary and secondary coils.The speed at which the magnetism changes.

Magnetic QuantitiesWith magnetism, we have the following quantities to deal with:

Magnetomotive Force - The quantity of magnetic field force, or "push." Analogous to electric voltage (electromotive force).Field Flux - The quantity of total field effect, or "substance" of the field. Analogous to electric current.Field Intensity - The amount of field force (mmf) distributed over the length of the electromagnet. Sometimes referred to asMagnetizing Force.

Flux Density - The amount of magnetic field flux concentrated in a given area.

Reluctance - The opposition to magnetic field flux through a given volume of space or material. Analogous to electrical resistance.

Permeability - The specific measure of a material's acceptance of magnetic flux, analogous to the specific resistance of a conductive material (), except inverse (greater permeability means easier passage of magnetic flux, whereas greater specific resistance means more difficult passage of electric current).

Factors Affect The Value Of Induced CurrentThe number of turns of the coilAs the number of turns increases, the magnitude of the induced current increases.

The speed of the relative motion of the conductor and the magnetic field As the speed of the relative motion of the magnet increases the magnitude of the induced current increases.

The strength of the magnet (magnetic field strength) As the strength of the magnet increases, the magnitude of the induced current will increase

ELECTROMAGNETICINDUCTIONMUTUAL INDUCTIONMAGNETIC QUANTITIESFACTORSNumber Of Turns Of The CoilStrength Of The MagnetSpeed Of The Relative Motion Of The Conductor Magnetomotive Force Field Flux Field Intensity Flux Density Reluctance Permeability