Ohm's Law
Ohm's law explains the relationship between current, I, measured in amps (A), resistance, R, measured in ohms (Ω), and potential, V, measured in volts (V),
and is written as
V=I×R
The voltage is measured between any two points in a circuit using a voltmeter.
Kirchhoff's Two Laws
The first of Kirchoff's two laws states that the sum of the currents at any point in a circuit must equal zero.
∑I=0
The second law states that the sum of the voltages in a closed loop must equal zero.
∑V=0
Power Law
When a current passes through a resistor, the temperature of the resistor increases and power (energy per unit time) is lost. The amount of power lost, P, is
the product of current and voltage, with units of Watts.
P=I×V
or, substituting in Ohm's law, we can express power as
P=I²×R=V²/R