Power

When consumers buy electricity they are purchasing Power.

The unit of power is the watt (W).

The formula for relating watts to voltage and current is:

P = E x I

Where

P = Power in Watts,

E = Voltage in Volts

I = Current in Amps

Watts = Volts x Amps

The Watt is the unit of power in the DC circuit

The Volt-amp is the unit of power in the AC circuit

When 5A is being sent through a resistor by a force of 200V.

The power in Watts is given by Volts x Amps

(P = E x I)

= 200V x 5A

= 1,000 W or 1KW (kilowatt)

If the volts and ohms are known, you can use formula 2 of Ohms law to find the amps.
The amps can then be substituted in the formula above to find the watts. If the current and resistance are known, formula 1 will give you the volts, which can then be substituted in the formula