We are familiar with electric heating device like water heater ,immersion heater ,electric stove etc. Careful observation of any electrical device reveals that some amount of heat is developed in all electrical devices.Let us discuss the cause of heating and the quantity of heat developed due to flow of electricity.
In 1841 Joule experimentally arrived at the mathematical relation now known after his name. He found that the amount of heat developed in a conductor depends on the quantity of current ,resistance of conductor and also on the time for which currents flows. He explained the heating of electrical conductor on the basis of the law of conservation of energy, The heat energy is developed due to transfer of energy from electrons to the ions and atoms in the conductor.
Now let us see how the energy of the electron gets transferred to ions and atoms. As electron gets transferred to ions and atoms. As electron moves through a conductor , they suffer collision with ions or atoms in their path and get decelerated . As a result a part of electron's KE is transferred to the atoms or ions of conductor. This increases the vibrational kinetic energy of atoms and causes rise in temperature.
In 1841 Joule experimentally arrived at the mathematical relation now known after his name. He found that the amount of heat developed in a conductor depends on the quantity of current ,resistance of conductor and also on the time for which currents flows. He explained the heating of electrical conductor on the basis of the law of conservation of energy, The heat energy is developed due to transfer of energy from electrons to the ions and atoms in the conductor.
Now let us see how the energy of the electron gets transferred to ions and atoms. As electron gets transferred to ions and atoms. As electron moves through a conductor , they suffer collision with ions or atoms in their path and get decelerated . As a result a part of electron's KE is transferred to the atoms or ions of conductor. This increases the vibrational kinetic energy of atoms and causes rise in temperature.
Joules Law Of Heating
According to Joule's law of heating the amount of heat developed in a conductor is directly proportional to
1.The square of the current intensity(I)
2.Resistance of conductor(R) and
3.Time for which current flows(t)
H=(I*I)Rt
The above relation can be obtained as follows:
The work required to drift the electrons by source of e.m.f connected across the resistance . If V is the potential difference across the resistance , then for each coulomb , V amount of work has to be done. Work done in drifting of charge q is W=qV ,
But q=It, where I is the steady current and V=IR
Total work W=(It)IR=(I*I)RT
The work done by the source is converted into heat .Heat developed is H=(I*I)Rt
Electric Power
Electric power of a device or circuit is the rate at which work is done by the source of e.m.f in maintaining the current.
Work done by the source W=(I*I)Rt
Power =Work/time
P=(I*I)R=IV=(V*V)/R
Electrical Energy
The total work done or energy supplied by a source of e.m.f in maintaining the electric current for a given time is the energy consumed by the circuit. The SI unit of energy is joule
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