Power output of an electric appliance

We know that power is the work done in a unit time. 

Just like in mechanical work, power is the rate of doing work in work done by 

electricity too. That is, power is the work done in a unit time or the energy consumed 

in a unit time.

Therefore the rate of energy consumption P by an electric appliance operated with 

a voltage V and drawing a current I is given by the following equation.

Power = voltage ×current

P = VI

When the voltage, V is measured in Volts (V) and the current, I in Amperes (A) the 

power, Pis given in Watts (W). 

Example 1

When a filament bulb is connected across a voltage difference of 12 V, a current of 

2 A flows through it. What is the power of the bulb?

Power  P= VI

= 12× 2 W

P= 24 W

Power of the bulb is 24 W.

Example 2

An electric oven operates under a 230 V power supply. If it has a power output of 

2000 W, find the current drawn when the oven is working.

P  = VI

∴ 2000  = 230× I

∴ I  =

2000

230

= 8.69 A

The current drawn by the oven is 8.69 A.

In the heating coils (heating element) of electric ovens, the energy consumed is 

converted only into heat. In some other appliances, part of the electric energy 

is converted into heat due to their internal resistance, while the remaining part is 

converted into other forms of energy.