Equation for electrical power

Answer 1

Google 'Ohms Law'

Answer

Ohm's Law has nothing whatsoever to do with power.

The fundamental equation for power in a d.c. system is: P = E I (where P = power, E = supply voltage, and I = load current). From this equation, two others can be derived: P = I2R and P = E2/R, where R = resistance.

For a.c. systems, the fundamental equation must be multiplied by the load's power factor (cosine of the phase angle).

Answer 2

Power (watts) is voltage times current.

Voltage is joules per coulomb. Current is coulombs per second. Multiply them together, and you get joules per second, which is also known as watts. Integrate that over time, and you get watt-seconds, or just plain joules. We also use the term kilowatt-hours; that is simply 3.6 million joules.

Of course, if the load is reactive, which it often is, the phase angle between voltage and current is non-zero, making apparent power (watts) not the same as true power (volt-amps, or VA). The ratio of watts over VA is Power Factor, and that is the cosine of the phase angle.

Answer 3

Scroll down to related links and look at "Formulas and calculations - Electricity and Electric Charge".