BEXS100 Basic Electricity

1
BEXS100 - Basic Electricity

• Unit 4
• Magnetism
• the basic laws governing magnetism and how they
  relate to electricity

2
Objectives
At the completion of this unit you will be able
to

• Understand the properties of permanent magnets
• Understand the operation of electromagnets
• Determine the polarity of an electromagnet
• Define terms used to describe magnetism and
  magnetic quantities

3
Introduction to Magnetism

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

4
Electromagnetics
Terms to remember

• Permeability - a measure of a materials
  willingness to become magnetized
• Reluctance - a materials resistance to magnetism
• Saturation - 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 stopped

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The Earth is a Magnet

• Geographic poles vs. magnetic poles
• lodestones
• Angle of declination

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THE FIRST COMPASS
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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
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The Electron Theory of Magnetism
What makes materials such as iron, nickel, or
cobalt, a natural magnetic material

• Electron spin theory
• Electrons become tiny permanent magnets
• Electrons in most materials spin in opposite
  directions
• Once paired they tend to cancel out any
  magnetic properties

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The Electron Theory of Magnetism
What makes materials like iron different than
most materials

• An Atom of iron contains 26 electrons
• 22 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 direction
• These 4 electrons account for the magnetic
  properties of iron

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The Electron Theory of Magnetism
What makes materials like iron different than
most materials

• As atoms combine to form molecules
• They arrange themselves to form a total of 8
  valence electrons
• In most materials the electrons cancel each other
  out
• In 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 Molecules

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Magnetic Domains/Molecules
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Magnetic Materials
The three basic classifications

• Ferromagnetic - metals that are easily
  magnetized iron, nickel, cobalt, manganese
• Paramagnetic - 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
  antimony

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
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Magnetic Lines of Force

• Magnetic lines of force are called flux
• Magnetic lines of flux repel each other never
  cross
• Lines 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
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Electromagnetics
A basic law of physics Whenever an electric
current flows through a conductor, a magnetic
field is formed around the conductor

• Electromagnets depend on electrical current flow
• They do not retain their magnetic field once
  current flow stops

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Electromagnetics
Factors that effect electromagnetic fields

• Winding 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 10
• The strength of the magnetic field is
  proportional to the amount of current flowing
  through the conductor

Ampere-Turns is determined by multiplying
the number of turns of wire by the current flow
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Electromagnetics
Core Materials magnetic/non-magnetic materials
around which the conductor is coiled
Two Types

• Air core electromagnets

• Core is made of Non-magnetic material

• Iron core electromagnets

• Made of magnetic materials
• Greatly increases strength of the magnetic field
  by increasing the number of flux lines

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Magnetic Measurement
The 3 different systems used to measure the
strength of a magnetic field

• The English System - flux density
• The CGS System - centimeter-gram-second
• The MKS System - meter-kilogram-second

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Magnetic Polarity
Determining the Polarity of an Electromagnet

• The Left-Hand Rule

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Demagnetizing
Disarranging molecules in a magnetic material
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Magnetic Devices

• Electromagnets
• Measuring instruments
• Inductors
• Transformers
• Motors
• GeneratorsAlternators

A Speaker uses both a permanent magnet and an
electromagnet
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Summary

• Energy is required to create a magnetic field,
  but no energy is required to maintain a magnetic
  field
• Unlike poles attract, like poles repel
• Whenever 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 field

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Elizabethtown Technical College Basic Electricity
BEXS100/101 Text Delmars Standard Textbook of
Electricity Unit 4 - Magnetism