Ohm's Law relates the three fundamental electrical quantities:
voltage, current and resistance. Power relationships are also given.
= I · R I = V
R = V
= I · V P = I2
· R P = V2
= Current (A)
P = Power (W)
R = Resistance (W)
V = Voltage (V)
Current (1st) Law
Voltage (2nd) Law
current flowing into a node or branching point
is equal to the sum of the individual currents
leaving the node or branching point.
algebraic sum of all the voltages around any
closed path in a circuit equals zero.
The Norton Equivalent of
a circuit consists of a Norton current source in parallel
with a Norton resistor and is valid for any load. In AC
circuits a Norton equivalent circuit is valid for a single
Norton current is the short-circuit current at the output
- the same as what is calculated for the Thévénin
short-circuit current (see Thévénin Equivalent page).
Norton resistance is the same as the Thévénin
The Thévénin Equivalent of
a circuit consists of a Thévénin voltage source in series
with a Thévénin resistor and is valid for any load. In AC
circuits a Thévénin equivalent circuit is valid for a single
voltage is the open circuit voltage at the output.
calculation is straightforward node or loop circuit
analysis. Using loop analysis:
Voc: [8 *
I1] + [(8+2+6) * I2] - [6 * I3] = 1 A
I2 = ½A ==> Voc =
½A * 6 W
= 3 V = Vth
Thévénin resistance from the open circuit voltage and the
short circuit current
(set RL = 0 and solve for I3) using Ohm's Law.
Rth = Voc
/ Isc = 3 V / [(4/9) A] = 27 / 4 W