DC Power

Power in DC circuits is calculated in the same way as Apparent Power in AC circuits:

Power = V I

= Voltage * Current

Units are Watts (W)

This equation can be combined with Ohms Law to give an expression for the power dissipated in a resistor as:

Power = I² R

= (Current through Resistor)² * Resistance

Units are Watts (W)

This is derived as follows:

Power = VI

V = I R (from Ohms Law)

Combining these gives Power = I I R

or Power = I²R