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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