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