Electric Power

1.0Definition

The work done per unit time by a source of emf (like a battery) in order to maintain electric current in a circuit is called ‘electric power’.

Consider a current I flowing through a resistor of resistance R. Let the potential difference across it be V (in figure). Let t be the time during which a charge Q flows across. The work done in moving the charge Q through a potential difference V is given by,

W = Q × V   … (1)

$\left(V=\frac{W}{Q}\right)$

Thus, the power input to the circuit by the source is

$P=\frac{W}{t}=\frac{Q\times V}{t}=\left(\frac{Q}{t}\right)\times V=I\times V$

or $P=VI$

2.0Unit of Electric Power 

SI unit : Watt  

Here, 1 Watt = 1 volt-ampere = 1 VA

1 kilowatt = 1000 watt

If the electric current through a device is one ampere and the potential difference across it is one volt, then its electric power is one Watt.

Also, power consumed by a resistor can be written as,

$P=VI=\frac{V^2}{R}=I^{2}R$ [Using, I= V/R and V=IR]

Every electric device is mentioned with a specified power and a specified voltage ; it works properly only if it runs at the specified voltage.

A 100-watt electric light bulb uses 100 joules of electrical energy every second.

If applied voltage is greater than specified voltage for an electric device, then the actual current exceeds its current capacity, the device will get damaged. If applied voltage is less than the specified voltage, then the current in the circuit will be less than the required; the device will not work properly.

3.0Also Read