Watts Law – Formula, Examples and Applications

Watt’s law describes the relationship among electric current, voltage, and electrical power. According to this law, the power in a circuit is a product of the voltage and the electric current. Watts law was named after James Watt, a Scottish engineer, and chemist. We will discuss Watt’s law, its formula, applications, as well as other related concepts in this article.

Watts Law Formula

Mathematically, watt’s law is given by

P = V × I

Where, P is power, V is voltage, and I is electric current


In an electric circuit, the voltage (V) represents the difference in potential between two points. Electric current will flow from a point of higher potential to a point of lower potential. The unit of voltage is the volt (V).

Electric current

It is a measure of how much electric charge is flowing through a given point in a circuit at any given time. It is measured in amperes (A). There must be a difference in the potential for current to flow.


Resistance (R) is defined as the opposition offered by the circuit to the flow of current. The resistance of an electrical component is a measure of its ability to resist the flow of current. It is measured in ohms (Ω).

Current, voltage, and resistance are related according to Ohm’s law. According to Ohm’s law, the amount of current flowing through a conductor is directly proportional to its voltage, i.e., I = V/R


In a circuit, power refers to the amount of work that can be performed or consumed by a component in a unit time. In simplest terms, power is the amount of energy transferred per unit time. The unit of power is the watt (W).
Watt’s law has many practical applications. By using Watt’s law, one can determine the voltage, power, ampere, and resistance of an electrical circuit.

Watts Law Example

1. When a light bulb is powered by 110 volts and has a power rating of 30 watts, what is the overall current?

The voltage and power of the bulb are therefore 110V and 30W, respectively. From watts law, current = Power/Voltage. Therefore, if we substitute the values, we obtain 0.273 Amperes of current.

What is the difference between Watt’s law and Ohm’s law?

Watt’s law describes the relationship between power, voltage, and current in a circuit, whereas Ohm’s law describes the relationship between resistance, voltage, and current.

These laws can, however, be combined to produce useful formulas. It is a well-known fact that Ohm’s law states that I = V/R and V = IR. By substituting these into Watt’s formula, we obtain

P = I × I × R = I2R


P = (V × V)/R = V2/R

Several other formulas can also be derived from these formulas.

Applications of Watts law

Here are a few applications of Watt’s law

1. You can use this formula to determine the actual amount of power that is generated by a power source. It can also be used to determine the power requirements of an individual component. In order to calculate the power requirement, you need to multiply the current and voltage.

2. Watt’s formula can be used to calculate the power requirements of a building. It is important to estimate the whole building’s power requirement when designing its wiring. This information can be used to determine the wire size that is suitable for your building. Additionally, it is possible to estimate the electricity costs associated with the system. A building’s power requirements are determined by determining the individual power ratings of all the electrical appliances or components it will contain and adding them together.

3. It is possible to determine the current of an electrical component by using Watt’s formula (I=P/V) when you know the power and voltage of the component.

4. It is possible to determine the voltage of an electrical component by using Watt’s formula (V=P/I) when you know the power and current of the component.

5. To determine the electrical resistance of a component, it is possible to use the formulas derived from the combination of Watt’s law and Ohm’s law. For example, we can calculate the electrical resistance of an electric bulb that is installed in a room using the formula R = P/V2.

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