Basic Electronic Formulas and Facts
Ohm's Law
 E = Voltage  measured in Volts
 I = Current  measured in Amperes
 R = Resistance  measured in Ohms
 E = I * R , answer in Volts
 I = E/R, answer in Amperes
 R = E/I, answer in Ohms
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Resistor Networks
 Resistors are labeled by a # following the R : R1...R2...Rn
 Rn = Continues for all the resistors you have.
 Rt = Resistance total
 Resistors in SERIES add : Rt = R1 + R2 +R3....+ Rn
 Two (2) Resistors in PARALLEL : Rt = ( R1 * R2)/(R1 + R2) This the Product divided by the Sum
 More than Two Resistors in PARALLEL: Rt = 1/ (1/R1 + 1/R2...+1/Rn) This is called the reciprocal formula
 Another form of this formula is : 1/Rt = 1/R1 + 1/R2.....+1/Rn
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Inductor Networks
 The rules for Inductors are exactly like those for Resistors
 Inductors are labeled by a # following the L : L1...L2...Ln
 Ln = Continues for all the Inductors you have.
 Lt = Inductance total
 Inductors in SERIES add : Lt = L1 + L2 +L3....+ Ln
 Two (2) Inductors in PARALLEL : Lt = ( L1 * L2)/(L1 + L2) This the Product divided by the Sum
 More than Two Inductors in PARALLEL: Lt = 1/ (1/L1 + 1/L2...+1/Ln) This is called the reciprocal formula
 Another form of this formula is : 1/Lt = 1/L1 + 1/L2.....+1/Ln
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Capacitor Networks
 The rules for Capacitor Networks are exactly opposite for those
of Resistors and Inductors.
 Capacitors are labeled by a # following the C : C1...C2...Cn
 Cn = Continues for all the Capacitors you have.
 Ct = Capacitance total
 Capacitors in PARALLEL add : Ct = C1 + C2 +C3....+ Cn
 Two (2) Capacitors in SERIES : Ct = ( C1 * C2)/(C1 + C2) This is the Product divided by the Sum
 More than Two Capacitors in SERIES: Ct = 1/ (1/C1 + 1/C2...+1/Cn) This is called the reciprocal formula
 Another form of this formula is : 1/Ct = 1/C1 + 1/C2.....+1/Cn
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Watt's Law
 P = Power  measured in Watts
 I = Current  measured in Amperes
 E = Voltage  measured in Volts
 R = Resistance  measured in Ohms
 P = I * E, answer in Watts  (easy as "pie")
 P = I*I*R, answer in Watts ( read as I squared R)
 P = E*E/R, answer in Watts ( read as E squared, divided by R)
 Note: Use Ohm's Law to derive other formulas for I , R, and E, using the formulas above.
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Calculating Reactance
 Inductive Reactance
 Pi = = 3.14
 f = Frequency, in Hertz
 L = Inductance of coil, in Henries
 Xl = Inductive Reactance, in Ohms
 , answer in Ohms
 Note: Xl is a linear function, it increases as frequency or inductor value increases.
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 Capacitive Reactance
 Pi = = 3.14
 f = Frequency, in Hertz
 C = Capacitance in Farads
 Xc = Capacitive Reactance, in Ohms
 , answer in Ohms
 Note: Xc is inversely proportional to frequency and capacitance. If either frequency or
capacitance increase, Xc decreases.
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Resonance in RLC Series Circuit
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Wavelength
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Frequency and Time
 f is the Frequency in Hertz/Second or Cycles/Second
 t is time in Seconds
 f = 1/t , answer in Hertz/Second or Cycles/Second.
 t = 1/f , answer in Seconds
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Impedance of a Circuit
 Xc = Capacitive Reactance, in Ohms
 Xl = Inductive Reactance, in Ohms
 R = Resistance, in Ohms
 Z = Impedance, in Ohms
 For a Capacitive circuit

 For an Inductive Circuit
 Rules for when you have a circuit with both Capacitive and Inductive Reactances
 When Xl is larger than Xc use the formula in figure (a)
, If Xc is Larger than Xl use the formula in Figure (b).

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