Magnetism Intro to magnetism and Electromagnetism. “the basic laws governing magnetism and how they relate to electricity”

Objectives: Understand the properties of permanent magnetsUnderstand the properties of permanent magnets Utilize terms used to describe magnetism and magnetic quantitiesUtilize terms used to describe magnetism and magnetic quantities Understand the operation of electromagnetsUnderstand the operation of electromagnets Determine the polarity of an electromagnetDetermine the polarity of an electromagnet At the completion of this unit you will be able to:

Introduction to Magnetism One of the most important phenomena in the study of electricityOne of the most important phenomena in the study of electricity The force of magnetism has been known for over 2000 years (Greeks)The force of magnetism has been known for over 2000 years (Greeks) Stones with magnetic qualities (magnetite) were first found in Magnesia in Asia MinorStones with magnetic qualities (magnetite) were first found in Magnesia in Asia Minor In the Dark Ages magnetism was thought to be caused by evil spiritsIn the Dark Ages magnetism was thought to be caused by evil spirits

The Earth is a Magnet Geographic poles vs. magnetic polesGeographic poles vs. magnetic poles lodestoneslodestones Angle of declinationAngle of declination

THE FIRST COMPASS

Permanent Magnets: Magnets that do not require any power or force to maintain their field One of the basic laws of magnetism states: “Energy is required to create a magnetic field, but no energy is required to maintain a magnetic field”

The Electron Theory of Magnetism Electron spin theoryElectron spin theory Electrons become tiny permanent magnetsElectrons become tiny permanent magnets Electrons in most materials spin in opposite directionsElectrons in most materials spin in opposite directions Once “paired” they tend to cancel out any magnetic propertiesOnce “paired” they tend to cancel out any magnetic properties What makes materials such as iron, nickel, or cobalt, a natural magnetic material

The Electron Theory of Magnetism An Atom of iron contains 26 electronsAn Atom of iron contains 26 electrons 22 of the electrons are “paired” and cancel each other out22 of the electrons are “paired” and cancel each other out The remaining 4 electrons located in the next to the outermost shell do not become “paired” and spin in the same directionThe remaining 4 electrons located in the next to the outermost shell do not become “paired” and spin in the same direction These 4 electrons account for the magnetic properties of ironThese 4 electrons account for the magnetic properties of iron What makes materials like iron different than most materials:

The Electron Theory of Magnetism As atoms combine to form moleculesAs atoms combine to form molecules They arrange themselves to form a total of 8 valence electronsThey arrange themselves to form a total of 8 valence electrons In most materials the electrons cancel each other outIn most materials the electrons cancel each other out In materials such as iron, the magnetic fields “add” rather than cancelIn materials such as iron, the magnetic fields “add” rather than cancel This “additive” effect forms regions in the molecular structure of the metal called: Magnetic Domains or Magnetic MoleculesThis “additive” effect forms regions in the molecular structure of the metal called: Magnetic Domains or Magnetic Molecules What makes materials like iron different than most materials:

Magnetic Materials Ferromagnetic - metals that are easily magnetized; iron, nickel, cobalt, manganeseFerromagnetic - metals that are easily magnetized; iron, nickel, cobalt, manganese Paramagnetic - metals that can be magnetized but not as easily as ferromagnetic; platinum,titanium,and chromiumParamagnetic - metals that can be magnetized but not as easily as ferromagnetic; platinum,titanium,and chromium Diamagnetic - metal or non-metallic materials that cannot be magnetized; copper,brass, and antimonyDiamagnetic - metal or non-metallic materials that cannot be magnetized; copper,brass, and antimony The three basic classifications: Note: Alloys often make the best permanent magnet materials. Combinations of such metals as aluminum, nickel, cobalt, copper, and iron (Alnico 5) are commonly used in the production of permanent magnets

Magnetic Lines of Force Magnetic lines of force are called “flux”Magnetic lines of force are called “flux” Magnetic “lines of flux” repel each other & never crossMagnetic “lines of flux” repel each other & never cross Lines of flux do not “flow” but it is assumed that they run North to SouthLines of flux do not “flow” but it is assumed that they run North to South One of the basic laws of magnetism: Unlike poles attract - Like poles repel

Electromagnetics Electromagnets depend on electrical current flowElectromagnets depend on electrical current flow They do not retain their magnetic field once current flow stopsThey do not retain their magnetic field once current flow stops A basic law of physics: Whenever an electric current flows through a conductor, a magnetic field is formed around the conductor

Electromagnetics Permeability - a measure of a material’s willingness to become magnetizedPermeability - a measure of a material’s willingness to become magnetized Reluctance - a material’s resistance to magnetismReluctance - a material’s resistance to magnetism Saturation - the point when an increase in current fails to significantly increase the magnetic fieldSaturation - the point when an increase in current fails to significantly increase the magnetic field Residual Magnetism - the amount of magnetism left once current flow has stoppedResidual Magnetism - the amount of magnetism left once current flow has stopped Terms to remember:

Electromagnetics Winding the conductor into a coil increases the strength of the magnetic fieldWinding the conductor into a coil increases the strength of the magnetic field A coil with 10 turns of wire will increase the magnetic field around the conductor by 10A coil with 10 turns of wire will increase the magnetic field around the conductor by 10 The strength of the magnetic field is proportional to the amount of current flowing through the conductorThe strength of the magnetic field is proportional to the amount of current flowing through the conductor Factors that effect electromagnetic fields: Ampere-Turns” “Ampere-Turns” is determined by multiplying the number of turns of wire by the current flow

Electromagnetics “Iron core” electromagnets“Iron core” electromagnets Core Materials: magnetic/non-magnetic materials around which the conductor is coiled Two Types: >Made of magnetic materials >Greatly increases strength of the magnetic field by increasing the number of flux lines “Air core” electromagnets >Core is made of Non-magnetic material

Magnetic Polarity The “Right-Hand Rule”The “Right-Hand Rule” Determining the Polarity of an Electromagnet

Magnetic Devices ElectromagnetsElectromagnets Measuring instrumentsMeasuring instruments InductorsInductors TransformersTransformers Motors Motors Generators;AlternatorsGenerators;Alternators A Speaker uses both a permanent magnet and an electromagnet

Summary Energy is required to create a magnetic field, but no energy is required to maintain a magnetic fieldEnergy is required to create a magnetic field, but no energy is required to maintain a magnetic field Unlike poles attract, like poles repelUnlike poles attract, like poles repel Whenever current flows through a conductor a magnetic field is formed around the conductorWhenever current flows through a conductor a magnetic field is formed around the conductor The direction of current flow through a conductor determines the polarity of the magnetic fieldThe direction of current flow through a conductor determines the polarity of the magnetic field