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MODULE V - FUNDAMENTALS OF ELECTRONICS REACTANCE What is Reactance? Reactance is the property of resisting or impeding the flow of ac current or ac voltage in inductors and capacitors. Note particularly we speak of alternating current only ac, which expression includes audio af and radio frequencies rf. NOT direct current dc. Inductive Reactance When ac current flows through an inductance a back emf or voltage develops opposing any change in the initial current. This opposition or impedance to a change in current flow is measured in terms of inductive reactance. Inductive reactance is determined by the formula: 2 * pi * f * L where: 2 * pi = 6.2832; f = frequency in hertz and L = inductance in Henries

Capacitive Reactance When ac voltage flows through a capacitance an opposing change in the initial voltage occurs, this opposition or impedance to a change in voltage is measured in terms of capacitive reactance. Capacitive reactance is determined by the formula: 1 / (2 * pi * f * C) where: 2 * pi = 6.2832; f = frequency in hertz and C = capacitance in Farads Some examples of Reactance What reactance does a 6.8 uH inductor present at 7 Mhz? Using the formula above we get: 2 * pi * f * L where: 2 * pi = 6.2832; f = 7,000,000 Hz and L = .0000068 Henries Answer: = 299 ohms What reactance does a 33 pF capacitor present at 7 Mhz? Using the formula above we get: 1 / (2 * pi * f * C) where: 2 * pi = 6.2832; f = 7,000,000 Hz and C = .0000000000033 Farads Answer: = 689 ohms Now in the real world we don't use big numbers like that, we use exponentials on our pocket calculator to get numbers like this: For inductive reactance where: 2 * pi = 6.2832; f = 7 X 10+6 Hz and L = 6.8 X -6 Henries Answer: = 299 ohms For capacitive reactance 1 / (2 * pi * f * C) where: 2 * pi = 6.2832; f = 7 X 10+6 Hz and C = 33 X -12 Farads Answer: = 689 ohms

Electron Theory and Atoms Resistance Resistors Ohms Law Current and Voltage Voltage Dividers Capacitance Inductance Reactance Resonance and Impedance Diodes Transistors "Q" Radio Terminology A-L Radio Terminology M-Z Atttenuators Chokes Decibel & Toroids Digital Basics Power Supplies Conclusion  Subscribe For A Free Ham Radio E-Tutorials  Back To Top

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