## Tuesday, January 26, 2016

### Krichoff's current law and Kirchoff's voltage law

As we know that Ohm’s law can be applied to circuits where there are resistive circuits only.  Now in electrical systems there are so many complex circuits consisting of lot of other load other than resistive loads. There are some circuits such as Bridge circuits which can’t be solved by using ohm’s law to find out voltages and currents circulating in the circuit. Kirchoff’s current law is used to solve the circuits to find out the current flowing the respective branches.

Kirchoff’s current law was given by Gustav Kirchoff in 1845. There are two laws given by Kirchoff naming as Kirchoff’s current law and Kirchoff’s voltage laws. KCL deals with current flowing in a closed circuit whereas KVL deals with voltage sources present in a closed circuit.
Kirchoff’s Current Law:-
According to this law “Total current entering a Junction or node is equal to current leaving the same junction or node”.  This means that algebraic sum of currents entering and leaving the junction or node is always zero. Currents entering the particular node are represented by positive and currents leaving the junction or node are presented as negative.
Kirchoff’s current law is also knows as Conservation of charges.
In Figure below you will see that at a particular Junction or node; Sum of currents entering the node= Sum of currents leaving the node
In figure you will see that:-

I1+ I2+ I3= I4+I5+ I6
Kirchoff’s current law can be used for analysis of parallel circuits.
Kirchoff’s Voltage Law:-
According to this law “in a closed network the total voltage around the closed circuit is equal to sum of voltage drops within the same circuit.”
This means that algebraic sum of all voltages within the closed circuit is always equal to zero. This law is also known as  Conservation of Energy.
In figure below you will see that in a closed loop there is direction of voltage drop is positive at point V12 and V23 but –ve in V34 and V41. So sum of all voltages in circuit is zero. It should be kept in mind that direction should be either selected as clockwise or anticlockwise for whole circuit.

Kirchoff’s voltage law is used to analyze Series circuit.

Kirchhoff's rules can be used to analyze any circuit this can be modified for those with EMFs, resistors, capacitors and more