ELECTRICAL ENERGY | JOULE'S LAW | ELECTRIC POWER

Electrical Energy And Joule's Law

   ELECTRICAL ENERGY: Turbine runs generator to produced electrical energy when water falls on it from higher gravitational potential to lower  gravitational potential. Similarly, when charge moves from a higher electrical potential to a lower potential, it delivers electric current. Thus, the process during which charges continuously move from higher potential to a lower potential, becomes a continuous sources of electrical energy.

Consider two points of potential difference of V volts. if one coulomb of charge passes between these points; the amount of energy delivers by the charge would be V joule. Hence, when Q coulomb of charges flows between these two points, then we will get QV joules of energy. If we represent this energy by W, then
Electrical energy supplied by Q charge W = QV joules .........................(i)
Now current, when charges Q flows in time t, is defined as:

         
                                      I = Q / t
      Or
                                     Q = It  ......................................(ii)

So the energy supplied by the charge Q in second  = W = V . I  .t ..................(iii)
This electrical energy can be converted into heat and other forms in the circuit.
From Ohm's law, we have V = IR
So the energy supplied by the Q charges is W = I . I . R . t   .............(iv)
Know The equation Becomes
                                              W= V . V . t / R

This Equation is called Joule's law, stated as:

The amount of heat generator in a resistance due to flow of charges is equal to the product of square of current I, Resistance R and the time duration t.

This energy can be utilized for different useful purpose. For example, bulb converts this energy into light, heat and heater and iron into heat, and fans into mechanical energy. Usually, this energy appears as heat in the resistance. This is the reason that we get heat in the resistance. This is the reason that we can get heat when current passes through heater.

Joule's Law

Electric Power

 The amount of energy supplied by current in unit time is known as Electric Power.

Hence power P can be determined by the formula 

                             Electric Power P = Electric Energy / Time = W/ T

Where W is the electrical energy given by 

                                  W = QV

Therefore, above equation becomes

Electric Power   P = QV / t = IV = I . I . R

When current I passes through a resistor R, the electric power that generators heat in the resistance is give by I . I . R.  The unit of electrical power is watt which is equal to one joule per second (1 j / s). It is represented by the symbol W. Electric bulb is commonly used in houses consumed 25 W, 40 W, 60 W, 75 W and 100 W of electric power.