Better to know some
... than all
Ohm's and Joule's Laws
NOTE: the symbol "V" is sometimes used to represent voltage instead of "E". In some cases, an author or circuit designer may choose to exclusively use "V" for voltage, never using the symbol "E." Other times the two symbols are used interchangeably, or "E" is used to represent voltage from a power source while "V" is used to represent voltage across a load (voltage "drop").
"The algebraic sum of all voltages in a loop must equal zero."
Kirchhoff's Voltage Law (KVL)
"The algebraic sum of all currents entering and exiting a node must equal zero."
Kirchhoff's Current Law (KCL)
Series circuit rules
* Components in a series circuit share the same current. Itotal = I1 = I2 = . . . In
* Total resistance in a series circuit is equal to the sum of the individual resistances, making it greater than any of the individual resistances. Rtotal = R1 + R2 + . . . Rn
* Total voltage in a series circuit is equal to the sum of the individual voltage drops. Etotal = E1 + E2 + . . . En
Parallel circuit rules
* Components in a parallel circuit share the same voltage. Etotal = E1 = E2 = . . . En
* Total resistance in a parallel circuit is less than any of the individual resistances. Rtotal = 1 / (1/R1 + 1/R2 + . . . 1/Rn)
* Total current in a parallel circuit is equal to the sum of the individual branch currents. Itotal = I1 + I2 + . . . In
Series and parallel component equivalent values
Series and parallel resistances
Series and parallel inductances
Series and Parallel Capacitances
Capacitor sizing equation
Inductor sizing equation
Time constant equations
Value of time constant in series RC and RL circuits
Time constant in seconds = RC
Time constant in seconds = L/R
Calculating voltage or current at specified time
Calculating time at specified voltage or current
AC circuit equations
Impedance in relation to R and X
ZL = R + jXL
ZC = R - jXC
Ohm's Law for AC
Series and Parallel Impedances
NOTE: All impedances must be calculated in complex number form for these equations to work.
NOTE: This equation applies to a non-resistive LC circuit. In circuits containing resistance as well as inductance and capacitance, this equation applies only to series configurations and to parallel configurations where R is very small.