Kirchhoff’s Laws *

These laws are more comprehensive than Ohm’s law and are used for solving electrical networks which may not be readily solved by the latter. Kirchhoff’s laws, two in number, are particularly useful

(a) in determining the equivalent resistance of a complicated net-work of conductors and (b) for calculating the currents flowing in the various conductors. The two-laws are:

1. Kirchhoff’s Point Law or Current Law (KCL)

It states as follows :  in any electrical network, the algebraic sum of the currents meeting at a point (or junction) is zero. 

                       I1 + (−I2) + (−I3) + (+ I4) + (−I5) = 0
                       or I1 + I4 −I2 −I3 −I5 = 0 or I1 + I4 = I2 + I3 + I5
                             or incoming currents = outgoing currents

2. Kirchhoff’s Mesh Law or Voltage Law (KVL)

It states as follows : The algebraic sum of the products of currents and resistances in each of the conductors in any closed path (or mesh) in a network plus the algebraic sum of the e.m.fs. in that path is zero.
 In other words, Σ IR + Σ e.m.f. = 0                                                           ...round a mesh
It should be noted that algebraic sum is the sum which takes into account the polarities of the voltage drops.



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