## The Electric Power Formula

Often you must have seen that electrical energy is produced from electrical generators and even other sources, such as electric batteries. In addition, businesses and households often use this supply through the electric power industry via an electric grid.

After that, electric companies measure the energy with the use of an electric meter, which keeps a total of electric energy distributed to a consumer. Electric power offers a rather low entropy type of energy. In addition, it can be carried over long distances. In addition, it can also be converted to other types of energy such as light, motion or heat.

Electrical energy is the speed at which energy is transferred to or from a part of an electrical circuit. A battery can supply energy, or a circuit element such as a resistor can release energy as heat. For any circuit element, the power is equal to the voltage difference in the element multiplied by the current.

According to Ohm’s Law, V = IR, so there are additional forms of the electrical energy formula for resistors. Power is measured in units of watts (W), where one watt equals one joule per second (1 W = 1 J/s).

**General form:**

Electrical Power = Voltage Difference x Current

P = VI

**Resistances:**

- P = electric power (W)
- V = voltage difference (V = J/C)
- I = electric current (A = C / s)
- R = resistance (Ω = V / A)

**Example of electrical energy formulas:**

1) If the battery of a cell phone works at 12.0 V and has to deliver a current of 0.9 A while playing music, what is the required power ?

**Answer: The required battery power can be found using the electric power formula:**

P = VI

P = (12.0 V) (0.9 A)

P = (12.0 J / C) (0.9 C / s)

P = 10.8 J / s

P = 10.8 W

**The power required by the phone battery is 10.8 W**

A historical note: it was James Prescott Joule, not Georg Simon Ohm, who first discovered the mathematical relationship between power dissipation and current through resistance. This discovery, published in 1841, followed the form of the last equation (P = I2R), and is correctly known as Joule’s Law.

However, these power equations are so commonly associated with Ohm’s Law equations relating voltage, current and resistance (E = IR; I = E/R; and R = E/I) that they are often credited to Ohm.

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