HEATING EFFECT OF ELECTRIC CURRENT: The phenomenon when a steady current flows through conductor the energy liberated during the current flow exhibited as heat
Consider a conductor of AB having potential difference V, potential at A is Va and potential at B is VB
If VA > VB
The potential energy of an electron at A is
UA = – q VA
Similarly
Potential energy of an electron at B is
UB = – q VB
If current flow through the conductor is (i) then amount of charge flows through the conductor in dt time is
dq = i dt
Number of electron flowing from end B to A in dt time is
\(\frac{q}{e}=\frac{Idt}{e}\)When electron moves from lower potential to higher potential there will be energy loss of electron (i.e., loss in potential energy)
\(dw=\left( \frac{Idt}{e} \right)\left[ \left( -e{{V}_{B}} \right)-\left( -e{{V}_{A}} \right) \right]\) \(=\frac{Idt\,\,e}{e}\left( {{V}_{A}}-{{V}_{B}} \right)\) \(dw=I\,dt\,v\) \(dw=V\,I\,dt\) ….. (1)Electrical power (p) is defined as
\(P=\frac{dW}{dt}=\frac{V\,I\,dt}{dt}\)P = V I ….. (2)
V = I R
P = V I = I2R
In general if electric current flows for a time t, the energy liberated will be
\(H=\frac{w}{J}\) \(J=4.2\,\,J/cal\) \(H=\frac{w}{4.2}=\frac{VIt\,}{4.2}\) \(H=\frac{{{I}^{2}}Rt}{4.2}\)Alternatively
When a steady current (i) flows for time (t) through a conductor by a source of emf E. then amount of charge that flow through conductor in time (t) is
Q = I t
Electrical energy delivered to charge flow through the conductor is
W = Q V = V I t
Thus, electric power given to the circuit is
\(P=\frac{W}{t}=\frac{VIt}{t}=VI\) \(P=VI={{I}^{2}}R\)Let as consider a simple circuit:
In the given circuit.
The rate at which chemical energy is converted into electrical energy is EI and power delivered across the external resistor R is I2R and power dissipated across the internal resistance of the cell is i2r, it can written as
\(EI={{I}^{2}}R+{{I}^{2}}r\)Since,
When a steady current flows through conductor, heat is produced in it. This is known as Joule’s Heating effect the heat developed across the external load resistance is given by
H = I2Rt
