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Outlines the electrical principles regarding magnetism and its relation to electromagnetism and also their key role in the function of other electrical devices and equipment.

Outlines the electrical principles regarding magnetism and its relation to electromagnetism and also their key role in the function of other electrical devices and equipment.


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  2. 2. The Earth Magnetic Poles North and South Geographic Poles North and South Earth is a giant magnet.
  3. 3. MAGNETISM Where does magnets come from? ⚫Centuries ago, it was discovered that certain types of mineral rock possessed unusual properties of attraction to the metal iron. One particular mineral, called lodestone, or magnetite.
  4. 4. Material is Magnetite or Iron Oxide (Fe2 03) Natural Magnet
  5. 5. What is Magnetism ⚫Certain metals attract other metals, this attraction is term magnetism. Materials that have magnetism is called magnets. ⚫Magnetism is produced as a result of electrons spinning on their own axes while rotating about the nuclei of atoms align. Magnetization usually results in
  6. 6. Properties of Magnets ⚫poles of opposite effect, denoted "north" and "south” ⚫Scientist later found out, that it was impossible to isolate one of these poles by itself by cutting a piece of lodestone in half: each
  7. 7. If you cut a magnet in half, you get 2 magnets! S N S N S N
  8. 8. Magnetic Materials ⚫A magnetic material is one that is attracted to a magnet and can be made into a magnet. ⚫One classification of magnetic materials are: diamagnetic, paramagnetic, and ferromagnetic material.
  9. 9. Diamagnetic materials ⚫Diamagnetic materials – these materials when placed in a magnetic field, opposes the direction of the magnetic field. ⚫ Examples: bismuth, antimony, copper, gold, quartz, mercury, water, alcohol, air, hydrogen etc.
  10. 10. Diamagnetic materials cont’d
  11. 11. Paramagnetic materials ⚫The paramagnetic materials are weakly attracted by the magnets when placed in a magnetic field. The paramagnetic materials feel an attractive force towards the strongest part of the field when they are placed in a non-uniform field. Aluminum, Chromium,
  12. 12. Ferromagnetic Material ⚫The ferromagnetic materials have very large values of magnetic permeability. They have the highest degree of magnetization. These are the magnetic materials, which are found to be attracted by magnets or
  13. 13. Ferromagnetic Materials Cont’d The previously un-magnetized iron becomes magnetized as it is brought closer to the permanent magnet. No matter what pole of the permanent magnet is extended toward the iron
  14. 14. ferromagnetic material cont’d a ferromagnetic material is one that readily and easily become magnetize.
  15. 15. Earth’s magnetic properties ⚫Gilbert was a scientist that showed that the Earth behaves as a magnet ⚫The Earth’s magnetic field is strongest at the poles ⚫Earth’s magnetic field is called the magnetosphere
  16. 16. Temporary magnets ⚫Easy to magnetize ⚫Lose their magnetism quickly ⚫Ex: Soft iron
  17. 17. Permanent magnets ⚫Hard to magnetize ⚫Stay magnetized longer than temporary magnets ⚫Ex: alnico (cobalt, nickel, aluminum)
  18. 18. Types of Magnets LOADSTON E BA R U COIL ALNIC
  19. 19. Questions ⚫How is a temporary magnet different from a permanent magnet? ⚫Give an example of a natural magnet.
  20. 20. What affects magnetic properties? ⚫Spinning electrons cause some metals to have magnetic properties ⚫Magnetic domains are groups of arranged magnetic fields ⚫Dropping,hammering or heating a magnet will cause a magnet to lose magnetic properties
  21. 21. 8J What’s a field? Field is a word we all understand – it’s a place with lots of grass! But scientists also use the word ‘field’ with another meaning. A field is an area where a force acts. So, a magnetic field is the area where a magnet could attract something. Can you think of any other sort of field in science? Magnetic Field
  22. 22. 8J What does a magnetic field look like? Well, we can’t see it for a start, but... Small particles of iron filings are pushed into patterns by a magnetic field. If we sprinkle iron filings on a piece of paper over a magnet we can see... The lines of force are very close together here – the field is very strong. The lines of force are further apart here – the field is weaker. A line of force links one pole of a magnet to the other pole.
  23. 23. 8J And the rule about directions... The magnetic force acts in a direction. The arrowheads on this diagram show you the way the needle of a compass point would go if it was free to move. You can see that the magnetic force runs from the north pole to the south pole of the magnet.
  24. 24. Poles attract or repel Laws of Magnets
  25. 25. Can you explain what the lines of force show? Where is the strongest part of the field?
  26. 26. Can you explain what the lines of force show? Where is the strongest part of the field?
  27. 27. Testing for Magnetism The only test for magnetism is repulsion. If a piece of metal is attracted by a magnetic, that only proves that the metal is made of a magnetic material. To prove that it is a magnet, it must REPEL another magnet. When two magnets are brought close to each other, there is a force between them. N S N S N S S N S N N S S N S N attra ct attra ct rep el rep el
  28. 28. Theory of Magnetism Molecular and Electron Theories
  29. 29. Questions ⚫Which scientist described the Earth’s magnetic properties? ⚫Name the devices used to indicate geographic direction based on the Earth’s magnetic field.
  30. 30. Magnetic Shielding ⚫The idea of preventing one component from affecting another through their common magnetic field is called shielding. In certain circuits stray magnetism can cause significant errors in measurement. ⚫Shielding materials are always metals, because of their high permeability; they are place over circuit component to block any
  31. 31. Creating Magnets ⚫The picture shows that a screwdriver does not pick up paper clips. Methods used to create a magnet
  32. 32. Creating Magnets Stroking using a permanent magnet ■ However, after stroking the screwdriver with a magnet, the blade itself becomes magnetic and attracts the paper clips.
  33. 33. Removing Magnetism Heat is one way to remove magnetism.
  34. 34. Mike Turner, Feb. 2004 Electromagnetism Whenever an electric current passes through a wire, a magnetic field appears around the wire. The shape of the field can be seen in the diagram. Click to move on The stronger the current is, the stronger the magnetic field. Some people believe that living near strong magnetic fields, such as those produced by power lines, can cause problems such as cancer. Lots of scientists are working to try to find out if this is true. At the moment, like many things in science, the definite answer is not known.
  35. 35. Electromagnetic Induction ⚫There is an induced emf whenever: ⚫A conductor ‘cuts’ magnetic field lines ⚫There is a relative motion between a magnetic field and a conductor ⚫There is a change in the strength of the magnetic field ‘linking’ a coil or circuit ⚫A coil is rotated in a magnetic field
  36. 36. Electromagnets To increase the strength of an electromagnet we can do three things : Add more turns to the coil of wire Use a bigger electric current Wrap the coil around a soft iron core If a steel core is used, the electromagnet will still be strong, but soon the steel will become permanently magnetised and the electromagnet will not be able to be switched off. We can make an electromagnet by coiling a wire and passing a current through it. This is often called a solenoid. The material that the coil is wrapped around is called the core.
  37. 37. Mike Turner, Feb. 2004 Using Electromagnets Electromagnets are very useful as they can be switched on and off, have their strength altered or their poles switched around. They are used in many things, especially when we want to create movement. Examples are : Motors Bells Loudspeakers Click to move on The shape of the field around an electromagnet is similar to the field around a bar magnet.
  38. 38. The Magnetic Field of a Wire An electromagnetic field is the magnetic field produce by current that forms circles around the conductor.The direction of the field lines can be determined using the right hand corkscrew rule. The strength of the field can be increased by increasing the current. Current Field Lines
  39. 39. WIRE IN A COIL ⦿To create a stronger magnetic field force with the same amount of electric current, we can wrap the wire into a coil shape, where the circling magnetic fields around the wire will join to create a larger field with a definite magnetic (north and south) polarity:
  40. 40. Magnetic Field Direction Cont’d A coil of wire used to create a magnetic field is called a solenoid.
  41. 41. Left-Hand Rule ⦿Detailed experiments showed that the magnetic field produced by an electric current is always oriented perpendicular to the direction of flow. ⦿A simple method of showing this relationship is called the left-hand rule.
  42. 42. Magnetic Field Direction Cont’d ⦿Simply stated, the left-hand rule says that the magnetic flux lines produced by a current-carrying wire will be oriented the same direction as the curled fingers of a person's left hand. ⦿(in the "hitchhiking" position), with the thumb pointing in the direction of electron flow:
  43. 43. Left-Hand Rule Cont’d
  44. 44. The left hand rule to determine North Pole NORTH POLE SOUTH POLE
  45. 45. Saturation Saturation Knee Y- Axis Increasin g Magnetic Force Y X- Axis Increasing Electric Current X Saturation of a magnetic field occurs when an increase of electric current flow does not increase the strength of the magnetic field as shown by the graph. The knee of the curve is the point that saturation occurs.
  46. 46. MAGNETIC UNITS OF MEASUREMENT ⚫Magneto-motive Force - the quantity of magnetic field force, or "push.” ⚫Field Flux - The quantity of total field effect, or "substance" of the field. ⚫Field Intensity - The amount of field force (mmf) distributed over the length of the electro-magnet.
  47. 47. MAGNETIC UNITS OF MEASUREMENT Cont’d ⚫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. ⚫Permeability - The specific measure of a material's acceptance of magnetic flux.
  50. 50. Electromagnetic Devices
  51. 51. Electromagnetic Devices
  52. 52. MAGNETIC TERMS ⚫Flux - Invisible lines of force. ⚫Poles - North and South where force is strongest. ⚫Permeability – The ability of a material to conduct lines of force. ⚫Residual Magnetism – The ability of a material to hold its magnetism for a long time.
  53. 53. MAGNETIC TERMS ⚫Ferromagnetic Material – A material easy to magnetize. (i.e., Iron Steel, Cobalt, Perm-alloy, and Alnico) ⚫Paramagnetic Material- A material that can be slightly magnetized. ⚫Diamagnetic Material – A material that is very difficult to magnetize. ⚫Magnetic Laws – Simply stated: Like poles repel and unlike poles attract.
  54. 54. Review ⚫What are the poles of a magnet? ⚫Name the magnetic lines of force. ⚫List three types of magnets and their two families. ⚫List the laws of magnets. ⚫Explain two methods for making a magnet.
  55. 55. Review ⚫Explain two theories of magnetism. ⚫Name five different types of devices that are associated with electromagnetism? ⚫List three magnetic and three nonmagnetic materials. ⚫What will remove magnetic lines of force?