Ohm's Law relates the three fundamental electrical quantities:
voltage, current and resistance. Power relationships are also given.

V
= I · R I = V
R = V
R
I

P
= I · V P = I^{2}
· R P = V^{2
}
R

I
= Current (A)
P = Power (W)
R = Resistance (W)
V = Voltage (V)

KIRCHHOFF'S
LAWS

Kirchhoff's
Current (1^{st}) Law

Kirchhoff's
Voltage (2^{nd}) Law

The
current flowing into a node or branching point
is equal to the sum of the individual currents
leaving the node or branching point.

The
algebraic sum of all the voltages around any
closed path in a circuit equals zero.

NORTON
EQUIVALENTS

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
frequency.

Original
Circuit

Norton
Equivalent Circuit

The
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).

The
Norton resistance is the same as the Thévénin
resistance.

THÉVÉNIN
EQUIVALENT

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
frequency.

The Thévénin
voltage is the open circuit voltage at the output.
calculation is straightforward node or loop circuit
analysis. Using loop analysis: