What is the heating effect of electric current, and how is heat produced in the circuit?

 Heating Effects of Current

The electric current through the resistor increases its thermal energy. Also, there is another situation in which an electric current can generate or absorb heat energy.

Power Supplied or Power Absorbed by a Battery

When a charge is transported across the source of the emf, its potential energy changes. If the net charge ∆ q moves through the potential difference E in time t, the change in electric potential energy of the charge is E∆ q. So, source of working emf is

                                  ∆W = E ∆ q

Dividing both sides by ∆t, then taking the limit as ∆t → 0,

                                     dW/dt = E dq/dt

By definition, dq/dt = i, the current through the battery and dW/dt = P, the power output of (or input to) the battery. Hence,

                                        P = Ei

The quantity P represents the rate at which energy is transferred from a discharged battery or to a battery charging.

Power dissipated across a resistance

Now consider the power consumed by the conductive element. There is resistance R,

The potential difference between its ends is V. when moving from a higher potential to a lower potential The Positive charge ∆q loses the energy ∆U = V ∆q. This electrical energy is absorbed by the conductor. The atomic lattice and charge carriers collide and the temperature rises. this effect is commonly referred as Joule heating effect. Because electric power is the rate at which energy is transferred, we have,

                            P = ∆U/∆t  = V ∆q /∆t = V i

                                  P =V i

which with the help of equation V = iR can also be written in the forms,

                              P =  I2R = V2/R

Power is always dissipated in resistance. With this rate, the heat produced in the resistor in time t is

                                     H = Pt

Joule heat is generated each time a current flows through a resistant element. To prevent

Delicate electronic components, overheating of many electrical devices such as videocassette recorders, TV and computer monitor chassis have fans that dissipate some of the heat

escape.

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