Electric Power Formula

Electric Power Formula

Electric power is defined as the rate at which work is performed by electricity. We measure it in watts. Furthermore, individuals use the term wattage to refer to the amount of electricity in watt. Electric devices are rated with electric power in watt which explains the amount of elctrical energy consumed per unit of time by the device. This post by extramarks covers electric power definition and formula to calculate electric power.

Electric Power Definition

Electric power pace at which electrical energy is delivered or used by an electrical circuit or device. It illustrates how much work an electric current can do in a given amount of time. The common units used to measure electric power are watts (W) or kilowatts (kW).

Electric power, like mechanical power, is a measure of how quickly work is completed. It basically determines rate of work done which means amount of work done per unit of time.

We have seen electric devices rated as 100 watt, this means it consumes 100 Joule of electrical energy in one second. We can understand it better using the electric power formula.

Electric Power Formula

Electric power is defined as the rate at which energy is moved to or from an electric circuit component. Energy can be supplied by a battery or a circuit component. Any circuit element’s power is equal to the voltage differential across the element multiplied by the current.

Therefore the formula of electric power is given as

P = VI


  • P is electric power
  • V is voltage difference
  • I is electric current

Power is measured in watts.

This means Watt Equals Joule per second. (1 W = 1 J/s). Hence, we can define one watt when 1 Joule of electricity is consumed in 1 second.

According to Ohm’s law we have V = IR

Putting the value of V in power formula we get

P = I²R = V²/R


  • Pis the electric power (W)
  • V is difference in voltage (V= J/C)
  • I is electric current (A = C/s)
  • R is resistance (Ω = V/A)

Power Energy Formula

The relation between power and energy is given as

P = E/t


E = P × t


  • E is energy
  • P is power
  • t is time

Solved Example of Electric Power

Q.1. The energy used by the iron for 5 minutes is 25 kJ, at a voltage of 250 volts. How large is the current in the iron?

Ans: Here, t = 5 minutes = 300 seconds

Energy = 25 Kilojoule = 25000 Joule

Voltage = 250 V

Electric power = P = W/t = 25000 Joule/300 seconds = 83.33 Watt

Therefore, Electric current (I) = P/V = 83.33 / 250 = 0.33 Ampere

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Electric Field Formula Poynting Vector Formula
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Ohms Law Formula Amperes Law Formula
Refractive Index Formula Horsepower Formula
Wavelength Formula Lattice Energy Formula
Stress Formula Length Contraction Formula

FAQs (Frequently Asked Questions)

1. Write the SI unit of electric power?

The SI unit of electric power is watt.

2. Is electric power a scalar quantity or vector quantity?

Electric power is scalar quantity.

3. Write the electric power formula and explain the terminology.

The electric power is given by P = VI, where V is the potential difference, I is the electric current and P is the electric power.