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Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz.

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Presentation on theme: "Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz."— Presentation transcript:

1 Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz

2 Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies 14 CHAPTER Magnetic Units

3 Topics Covered in Chapter 14  Ampere-turns of Magnetomotive Force (mmf)  Field Intensity (H)  Permeability (  )  B-H Magnetization Curve

4 Topics Covered in Chapter 14 (continued)  Magnetic Hysteresis  Ohm's Law for Magnetic Circuits  Relations between Magnetic Units  Comparison of Magnetic and Electric Fields

5 Ampere -Turns Ampere-turns = I  N  I  N specifies the amount of magnetizing force or magnetic potential (mmf).  I is the amount of current flowing through N turns of wire.

6 Magnetomotive Force (At) Ampere-turns = I x N. I N

7 Field Intensity (H) Equation: H = mmf/length Units: A·t/m ampere-turns per meter Shorter magnetic circuits produce a greater field intensity.

8 Field Intensity (H) length (ampere-turns per meter)H = A·t/m The field intensity in the core is inversely related to length.

9 0 1k 2k 3k 4k 5k H in At/m B in Teslas 0.5 B-H Magnetization Curve B meter Soft iron Saturation

10 Hysteresis Loop - H+ H + B - B + B max - B max + B R - B R - H C B R is due to retentivity. (Note that H = 0 but B > 0.) H C is the coercive force. (that needed to make B = 0) + H C

11 Demagnetization (Also Called Degaussing) B R is reduced to zero.

12 Hysteresis Curve When Retentivity is Very Low - H+ H + B - B + B max - B max

13 Permeability (  )  Equation:  = B/H  Unit: T Atm  / Permeability is a measure of the ability to concentrate magnetic fields. teslas per ampere-turn per meter

14 Permeability drops drastically at saturation. - H+ H + B - B + B max - B max Slope of B/H is small Slope of B/H is large

15 Reluctance Reluctance is the opposition to flux. It is comparable with resistance in an electrical circuit.  Equation:  = mmf /   Units: A·t/Wb ampere-turns per weber

16 Permeance Permeance is comparable with conductance in an electrical circuit (G = 1/R).  Equation:   Units: Wb/A·t webers per ampere-turn

17 Ohm’s Law for Electrical and Magnetic Circuits Electrical circuits: I = V/R Magnetic circuits:  = mmf / 

18 Increasing reluctance decreases flux. Adding an air-gap increases the reluctance. I As  increases,  decreases.


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