Electric Power Formula

Electric Power Formula

It is essential in measuring the efficiency of an electric circuit by calculating the rate of transfer of energy in it. Below let us know more about its formula with examples.

Definition

The measurement of the rate at which energy is transferred in an electric circuit or the rate at which work is done in the electric circuit is called the electric power of the circuit.

It can also be defined as the amount of energy consumed in a particular period.

You should have frequently seen electric power created from electric generators and, surprisingly, different sources like electric batteries. In addition, our house receives this supply of energy through a power grid from the electric industry. The electric power utilized in a particular household is measured using an electricity meter to know the total amount of energy consumed by the consumer.

• Power is denoted by the symbol P.

• SI unit is Watt, Joule per second.

• It is a scalar quantity

Formula

The main formula for power is 

P = VI

Where, P is power

V is the Potential difference in the circuit.

And, I is the electric current in the circuit.

We can also write it as, 

By using Ohm’s Law V = IR, R being the resistance in the circuit.

P = I²/R

P = V²/R

Now let us see the relation between power and energy.

P = E/t

E is the energy and t is the time per second.

Also,                                              P = VQ/t

Where, V is the potential difference and Q is the charge (in Coulombs).

Some Solved Examples

Q1. The battery of a cell phone works at 15.0 V. Also, it necessities to give a current of 0.5 A when music plays, what is the amount of power required to do so?

Solution: 

Given: V = 15.0 V,         I = 0.5 A,   P = ?

The formula used here is
P = VI

P = 15 ×0.5

P = 2.5 W

Hence, the required power is 2.5 W.

Q2. A resistor has a potential difference of 30.0 V and produces heat. The thermal power produced in the process is 12.0 W. What is the resistance value in the resistors?

Solution: 

Given: V = 30 V,         P = 12 W,     R = ?

Here we will use the formula,
P = V²/R

12 = (30)²/R

R = 900/12

R = 450/6

R = 75 Ω

Hence, resistance in the resistors is of 75 Ω.