# Electrical Theory Quantity Symbol Unit Equation

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Electrical Theory Quantity Symbol Unit Equation
Charge Q coulomb Q = IIdt Current I ampere I = dQ/dt Voltage V volt V = dW/dQ Energy W joule W = IVdt = IPdt Power P watt P =dW/dt = IV Resistor R ohm V = IR Inductor L henry V = L dI/dt Capacitor C farad V = 1/C IIdt

Electrical Theory Ohm’s Law I =V/R (DC) I = V/Z (AC) Kirchoff ’s Law
Sum of Loop Voltages = 0 Sum of Node Currents = 0 Joule’s Law P = IE = I2R (I Squared R Loss)

Current Flow Electron Flow - From excess to deficient
Conventional Current Flow Internal to Source (Battery) Negative to Positive External from Source (Battery) Positive to Negative Voltage Drop - Across a Resistor + to - Negative Current - Assumed Direction Reversed

Equivalent Circuits Thevenin Two Terminal Resistor and Battery Circuit
Series Voltage Source and Equivalent Resistor Voltage Source = Open Circuit Voltage Equivalent Resistor = V / Short Circuit Current Norton Parallel Voltage Source and Equivalent Resistor Current Source = Short Circuit Current

Series and Parallel Components
Component Series Parallel R Req = R1 + R2 + R3 1/Req = 1/R1 + 1/R2 +1/R3 Z Zeq = Z1 +Z2 + Z3 1/Req = 1/Z1 + 1/Z2 + 1/Z3 l Leq = L1 + L2 + L3 1/Leq = 1/L1 + 1/L2 + 1/L3 C 1/Ceq = 1/C1 + 1/C2 + 1/C3 Ceq = C1 + C3 + C3

DC Circuit Components Component Impedance Current Power Energy
R R I = V/R None L Zero Infinite WL = 1/2 LI2 C Infinite Zero WC = 1/2 CV2

AC Sinusoidal Analysis
Resistor R I = V/R P = I2R = V2/R Inductor jXL= jwL I = -jVL/wL QL= I2XL = VL2/XL Capacitor -jXC= -j/wC I = jVCwC QC= I2XC = VC2/XC Current I = IR + j IX Voltage V = VR + j VX Complex Power S = VI* = (VR + j VX)(IR - j IX) Complex Power S = P + j Q