Electric Power

In physics, electric power measures the rate of electrical energy transfer by an electric circuit per unit of time. Denoted by P and measured using the SI unit of power which is watt or one joule per second. Electric power is commonly supplied by electric batteries and produced by electric generators.

Electric Power Definition

Electric power is the rate at which work is done or energy is transformed into an electrical circuit. Simply put, it is a measure of how much energy is used in a span of time.

Symbol P
SI Unit Watt, joule per second
Scalar or Vector Scalar Quantity
Formula P = VI

Electric Power Formula

The formula for electric power is given by

P = VI

where,

P is the power

V is the potential difference in the circuit.

I is the electric current.

Power can also be written as

P = I2R
P = V2/ R

The above two expressions are obtained by using Ohm’s law, Where, voltage, current, and resistance are related by the following relation:

V = IR
Where,

  • R is the resistance in the circuit.
  • V is the potential difference in the circuit
  • I is the electric current

Electric power

Power-Energy Formula

Since power is the rate of energy consumption, energy can directly be calculated using

\(\begin{array}{l}P=\frac{E}{t}\end{array} \)

Where,

E is the energy consumption (in Joules)

t is the time in seconds

\(\begin{array}{l}P=\frac{VQ}{t}\end{array} \)

Where,

  • Q is the charge (in Coulombs)
  • V is potential difference in volts
  • t is the time in seconds

Related Physics Concepts

Electric Power Problems

Based on the information given above, try the application problem given below:

Example:

A 9V battery is connected to a resistor having a resistance of 10 Ω. What is the current and power across the resistor?

Solution:

I = V/R = 9/10 = 0.9 A

P = VI = 9 × 0.9 = 8.1 J/s or 8.1 W

Frequently Asked Questions – FAQs

Define electric Power.

Electric power is the rate at which work is done or energy is transferred in an electrical circuit. Simply put, it is a measure of how much energy is used in a span of time.

Write the SI unit of electric power

The SI unit of electric power is watt.

Write the electric power formula and explain the terms.

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.

Is electric power a scalar quantity or vector quantity?

Electric power is scalar quantity.

How can we express power using Ohm’s law?

The power formula can be rewritten using Ohm’s law as P =I2R or P = V2/R, where V is the potential difference, I is the electric current, R is the resistance, and P is the electric power.

Why shouldn’t you touch electrical equipment with wet hands? Find out answer to this question by watching the video.

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