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Chapter 16 - PowerPoint PPT Presentation


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Chapter 16. Magnetism and Magnetic Quantities. Magnetism and Electricity. You can’t have one without the other Magnetism is typically an attraction of iron (but can be other materials). Where does Magnetism come from?. As opposed to electricity, we don’t know for sure

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Chapter 16


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  1. Chapter 16 Magnetism and Magnetic Quantities

  2. Magnetism and Electricity • You can’t have one without the other • Magnetism is typically an attraction of iron (but can be other materials)

  3. Where does Magnetism come from? • As opposed to electricity, we don’t know for sure • There are only theories such as those in the book. • We know how it works though

  4. History of Magnetism • First truly studied by William Gilbert in 1600 • Characterized magnets as having 2 poles

  5. History of Magnetism (continued) • In 1820 Hans Christian Oersted discovered that a current carrying conductor generates a magnetic field.

  6. ElectroMagnetism • Thus you can create an electromagnet • An electromagnet consists of a coil of wire wrapped on an iron core and generates magnetic flux when electricity is allowed to pass through it. This is not how real nail guns work, (they use real compressed springs that slam a trigger hammer).

  7. How a speaker works • Uses a permanent magnet http://www.youtube.com/watch?v=_otCquvos8o http://www.youtube.com/watch?v=mFiZZyV-YCo Only to 2:20

  8. Applications for Electromagnet • Relay • Bells • Buzzers • Ferrites Ferrites block high frequencies from coming through

  9. Strength of ElectroMagnet • The strength of the magnetic field depends upon: • 1 The number of coils • 2 The strength of the current • 3 The magnetic permeability of the core material.

  10. Magnetism Video • http://www.youtube.com/watch?v=uj0DFDfQajw&feature=fvw

  11. Magnets Divided • There are only two types of poles to be found: north and south (by analogy, positive and negative)

  12. Properties of a Magnet • Permeability – the ease at which a material can pass magnetic lines of force (Much like conductance) • Reluctance – the opposition that a material offers to the magnetic lines of force (Much like resistance)

  13. Magnet Types • Temporary Magnets – magnets that easily lose their magnetic strength after their magnetizing force has been removed • Permanent Magnets – magnets that retain their magnetic strength despite their surroundings.

  14. Magnetic Field • Magnets produce a “magnetic field” around themselves. • The lines making up the magnetic field are called magnetic lines of force or Flux Lines.

  15. Magnetic Field (cont.) • Flux lines leave the North pole of the magnet, make their way around through the surrounding space and enter in through the South pole of the magnet. • A Flux line is denoted by  (PHI) • 100 million flux lines = 1 Weber (Wb)

  16. Characteristics of Magnetic Lines of Force (Flux Lines) • 1. Flux lines are continuous and always form a closed loop • 2. Flux lines never cross one another. • 3. Flux lines tend to shorten themselves. So flux between two poles (N and S) tend to squeeze the poles together. • 4. Flux lines pass through all material both magnetic and non-magnetic • 5. Flux lines leave a pole perpendicular to it.

  17. Magnetic Attraction and Repulsion • Like magnetic poles repel each other • Unlike poles attract each other • This attraction/repulsion affect varies directly with the product of their strength and inversely with the square of the distance between them.

  18. Magnetic Attraction and Repulsion (cont.)

  19. Random Video of the Day http://www.youtube.com/watch?v=4e2AINr0kJE

  20. Classifying Magnetic Materials

  21. Types of Magnets • All magnets are fake (or artificial) except for magnetite and Earth Permanent Magnets – After being exposed to the presence of a magnetic field they retain there magnetism even after the field is no longer there. The only way a permanent magnet can lose its magnetism is by: High Temperatures Physical Shock Strong Demagnetizing force

  22. Magnetic Shielding • No known perfect insulator for magnetic flux. (Increasing distance is your best bet) • As opposed to electrical insulation • Ie: computer towers are not immune, this is why they make them out of soft-iron

  23. Magnetic Quantities

  24. Chapter 17

  25. Types of DC motors Series Motors: Windings are connected in series with Armature Starting torque is greater than other DC motors Speed varies widely with load Shunt Motors: Windings are connected in parallel with Armature Starting torque is smaller than other DC motors Speed does not vary widely with load Compound Motors: A mixture of series and shunt Stepper Motors: Motors that turn a specific amount of time Used in printers, scanner, disk drives… (Micro-controllers drive stepper motors)

  26. Brushless DC Motors In a BLDC motor, the electromagnets do not move; instead, the permanent magnets rotate and the armature remains static.