Electric power, definition, units, formula with example

Friends, today we will read about electric power and know where it is needed and how we get it out. How important it is in our life.

Electric Power:- 

1)The amount of electric energy consumed per unit time (1 sec) in any electrical or electronics appliance is called electric power.

P = E / T

P = Power                                                                                             

E = Energy

T = Time

                                                                   OR

2)Any electrical or electronics appliance will do as much work per unit time (1 sec), we call it electric power.

P = W / T

P = Power                                                                                             

W = Work

T = Time

It means to say that if the power of a device is more then it will work in less time and if the power of a device is less then it will take more time to work. Like suppose there are two water filled motors.

One motor is of 1 KW and the other motor is of 500 W, so we know that a motor of 1 KW will fill water quickly i.e. in less time and a motor of 500 W will take more time to fill water.

S.I Unit of electric power:-

We have read already P = E / T               

               

We know that the S.I unit of electric energy (E) = joule

Than P = Joule / Second 

         P = J . S^-1 (Watt)

The S.I unit of electric power is Watt (W)

 We can say that power is said to be 1W if 1A current flows through a circuit having 1V pottential difference.

1W = 1V X 1A

 1W = V . A

Formula of electric power:-

If an electronics or electrical device is running, then it is obvious that there is movement of electrons inside it. The movement of electrons means that the current in the device is moving. 

The device will also be hot due to current movement. This means that electrical energy in the device is converting into heat energy. So we can also say power such as.

                                               P = H / T                                       

P = Power                                                                                             

H = Heat energy

T = Time  

 Heat (H) = I² RT

P = I² RT / T

P =  I² R ------------ (i)

According to Ohm's law

 V = IR

We can say that

R = V / I

Put the value of R in Eq (i)

P =  I² R

P =  I²  V / I

P =  V . I--------------(ii)

According to Ohm's law

 V = IR

We can say that

I = V / R

Put the value of I in Eq (i)

P =  I² R

P = V²  / R^{2  .} R   

P = V² / R-----------------(iii)

Commercial unit of electric power:-

The commercial unit of electric power is kilo watt hour (KWH) .

^{1KW = 1000 W} 

^{1 Hour = 3600 Seconds}

^{1KWH = 1000 W X 3600 S}

^{1 KWH = 1000 Joule / Second  X 3600 Second}

^{1KWH = 3600000 Joule}

1KWH = 36 x 10⁵ J 

        ^{Or we can say}    

1KWH = 3.6 x 10⁶ J  

^{Solved Example}

Example - An electric bulb run from 220V mains. The current flowing through it is 0.5A. At which rate is the electrical energy transformed by bulb? How much energy is transformed in 6 hour?

Solution -  Now read the question carefully and see what we have to find out of it. In this question, we have to find electric energy. So we know what is the formula of electric energy.

As you know     P = E / T

Than                  E = P . T 

We have been given time here but electric power is not given. So first we will find electric power. Here we have given the value of voltage and current to get electric power.

As you know        P = V . I

                             P = 220 X 0.5

                             P =  110 W or J / S  

Now we have found out electric power here and now we will also easily find electric energy. This bulb gives 110 W power in 1 second. First we will take 6 hours time of bulb.

1 minute = 60 sec

1 hour = 60 X 60 sec

1 hour = 3600 sec

6 hour = 3600 X 6 sec

6 hour = 21600 sec

Now we have found out time here and now we will also easily find electric energy.

E = P X T

E = 110 J/S X 21600 S

E = 2376000 Joule

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Ishan Kumar