Thermal Effect of Current

(1) Introduction

  • We have already learned the electric current and the physics behind it in the previous chapter
  • We have also discussed the mechanism of flow of current in a conducter but not the physical consquences of flow of elctric current are related to other forms of energy
  • In this chapter we will study about causes and consequences of electric current
  • In the nutshell ,what we will study in this chapter is the connection between the electricity and thermal energy.

(2) Heating effect of current

  • In previous chapter while discussing electric energy and power ,we learned that IΔV amount of energy is lost per second when a current I flows through a potential ΔV and this energy appears in the form of heat energy
  • Due to the conversion of electric energy into heat energy the conductor becomes hot .This effect is known as Joule's Heating and this heating is thermodynamics irreversible.

    Cause Behind Joule's Heating:-

  • Explanation behind the Joule's heating is that when a potential difference ΔV is maintained between the ends of a conductor,the free electrons in the conductor are accelerated towards the higher potential end of the conductor
  • In their way electrons frequently collided withe the positive ions of the conductor due to which their velocity decreased
  • This the energy electrons gained on account of acceleration is transferred to the positive lattice ions or atoms and electrons then returns to their equilibrium distribution of velocities
  • Thus ,lattice ions receives energy randomly at the average rate of IΔV per unit time
  • Ions spends this energy by vibrating about their mean positions resulting in rise in the temperature of the conductor
  • This way Joule's heating nothing but the conversion of electrical energy into heat energy

(3) Thermoelectricity

  • We know that currents flows in a conductor whenever there is a electric potential difference betweens the ends of the conductor
  • If there is a temperature difference between the ends of the conductor then thermal energy flows from hotter end to the colder ends
  • Thermal energy flows may also be carries by the electrons in the conductor and hence resulting the presence of electric current
  • At the hotter end of the conductor electrons have slightly higher kinetic energy and hence they move faster
  • So there is net flow of current towards the end of the conductor with lower temperature.Thus an electric current exists in the conductor due to the difference in the temperature of two ends of the conductor
  • This phenonmenon due to which electricity is produced when two ends of the conductor are kept at different temperature is known as thermoelectricty

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