1. Electronics Technology Fundamentals Chapter 8 Magnetism

2. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 2 8.1 Magnetism: An Overview – P1 Magnetic Force – the force that a magnet exerts on the objects around it

3. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 3 8.1 Magnetism: An Overview – P2 Magnetic Poles – The points where magnetic lines of force leave (and return to) a magnet Lines of force are assumed to emanate from the north-seeking pole (N) and to return to the magnet via the south-seeking pole (S) Within the magnet, the lines of force continue from (S) to (N)

4. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 4 8.1 Magnetism: An Overview – P3 Like and Unlike Poles

5. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 5 8.1 Magnetism: An Overview – P4 Magnetic Flux – the lines of force produced by a magnet Two units of measure Unit of Measure Unit SystemValue (defined) Maxwell (Mx)cgs1 Mx = 1 line of force Weber (Wb)SI1 Wb = 1 X 10 8 Mx

6. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 6 8.1 Magnetism: An Overview – P5 Magnetic Flux – practical unit of measure The maxwell is not a practical unit of measure as it is too small The weber is not a practical unit of measure as it is too large The microweber (μWb) is the preferred unit of measure 1 μWb = 100 Mx

7. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 7 8.1 Magnetism: An Overview – P6 Magnetic Field – the area of space surrounding a magnet that contains magnetic flux

8. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 8 8.1 Magnetism: An Overview – P7 Flux Density – a measure of flux per using area (often referred to as field strength) Unit of Measure – tesla (T) = 1 Wb/m 2 where B = the flux density  = the amount of flux A= the cross-sectional area containing the flux

9. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 9 8.1 Magnetism: An Overview – P8 Insert Figure 8.4

10. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 10 8.2 Magnetic Characteristics of Materials – P1 Permeability (  m ) – a measure of the ease with which lines of magnetic force are established within a material

11. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 11 8.2 Magnetic Characteristics of Materials – P2 Relative Permeability (  r ) – the ratio of a material’s permeability to that of free space (  0 ) where  r = the relative permeability of the material  m = the permeability of the material, in Wb/A·m  0 = the permeability of free space, 4  X 10 -2 Wb/A·m

12. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 12 8.2 Magnetic Characteristics of Materials – P3 The Source of Magnetism: Domain Theory – atoms with like magnetic fields join together to form magnetic domains

13. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 13 8.2 Magnetic Characteristics of Materials – P4 Magnetic Induction – the process of producing an artificial magnet

14. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 14 8.2 Magnetic Characteristics of Materials – P5 Retentivity – the ability of a material to retain its magnetic characteristics after a magnetizing force has been removed High retentivity materials tend to have low permeability High retentivity materials used for permanent magnets Low retentivity materials used for temporary magnets

15. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 15 8.2 Magnetic Characteristics of Materials – P6 Reluctance – the opposition that a material presents to magnetic lines of force Unit of Measure SI Unit - amperes per weber (A/Wb) cgs Unit – gilberts per maxwell (Gb/Mx)

16. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 16 8.2 Magnetic Characteristics of Materials – P7 Reluctance (Continued) where  = the reluctance of the material ℓ = the length of the material  = the permeability of the material A= the cross-sectional area of the material

17. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 17 8.2 Magnetic Characteristics of Materials – P8 All materials can be classified according to their magnetic characteristics Ferromagnetic: magnetic Paramagnetic: slightly magnetic Diamagnetic: nonmagnetic

18. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 18 8.3 Electromagnetism – P1 1820, H.C. Oersted (a Danish phyicist) – discovered electric current produces magnetic field

19. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 19 8.3 Electromagnetism – P2 Current-carrying wire generates lines of magnetic force

20. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 20 8.3 Electromagnetism – P3 The Left-Hand Rule – a memory aid that helps you to determine the polarity of the magnetic field that results from the current through a wire

21. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 21 8.3 Electromagnetism – P4 The Coil – a wire wrapped into a series of loops for the purpose of concentrating magnetic lines of force

22. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 22 8.3 Electromagnetism – P5 Magnetomotive Force (MMF) – mmf is to magnetic circuits what electromotive force (emf) is to electric circuits Unit of Measure – ampere-turns (A·t) Magnetic equivalent to electromotive force (EMF)

23. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 23 8.3 Electromagnetism – P6 Magnetomotive Force (Continued) Rowland’s law where  = the magnetic flux, in webers (Wb) F = the magnetomotive force, in ampere-turns (A·t)  = the reluctance, in ampere-turns per weber ( A·t/Wb)

24. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 24 8.3 Electromagnetism – P7 Ampere-Turns – product of the number of turns and the coil current Represented using NI (N for number of turns, and I for current) MMF = NI

25. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 25 8.3 Electromagnetism – P8 Flux density produced by a coil where B = the flux density, in teslas (T)  m = the permeability of the core material, in Wb/ A·m NI= the ampere-turns value of the coil ℓ = the length of the coil, in meters (m)

26. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 26 8.3 Electromagnetism – P9 Common Application: Tape Recording Head

27. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 27 8.3 Electromagnetism – P10 Hysteresis – the time lag between the removal of a magnetizing force and the drop in flux density

28. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 28 8.3 Electromagnetism – P11 Hysteresis Curves

29. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 29 8.4 Magnetic Relays: An Application of Electromagnetic Properties – P1  Basic Magnetic Relay

30. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 30 8.4 Magnetic Relays: An Application of Electromagnetic Properties – P2  Reed Relays

31. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 31 8.5 Related Topics – P1 Magnetic Shielding Used to insulate a magnetically sensitive device from the effects of the magnetic flux Accomplished by diverting lines of magnetic flux around (or away from) an object to be shielded

32. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 32 8.5 Related Topics – P2 Ring Magnets Magnets without any identifiable poles or air gaps that do not generate an external magnetic field Commonly used in analog meter movements

33. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 33 8.5 Related Topics – P3 Care and Storage – Common causes for loss of magnetic strength for a permanent magnet Jarring or dropping High Temperature Improper Storage – necessary to ensure that the flux produced by the magnet is not lost externally

34. Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. 34 8.5 Related Topics – P4 Care and Storage (Continued)