Circuit Theory Tashfeen Khan

Introduction This chapter mainly deals with laws that are used to find currents, voltages and resistances in a circuit. These laws are the Kirchhoff current law, Kirchhoff voltage law, current division rule and voltage division rule.

Basic terminologies Node is a point at which two or more elements connect with each other. If we move from one node to another such that no node was encountered more than once, then the set of nodes and elements that we have passed through is called a path. If the node at which we start our path is the same at which we end, then the path is defined as loop. A branch is defined as an element with nodes on each end.

Kirchhoff Current Law It states that sum of currents entering a node is equal to zero. For example if there are four currents entering a node, we can write that – i1 + i2 + i3 + i4 = 0 Another definition could be that sum of currents entering = sum of currents leaving

Kirchhoff voltage Law It states that sum of voltages around a closed path is equal to zero. For example if there are four voltages around a closed path then we can write that – v1 + v2 + v3 + v4 = 0 We have to see that all voltages added should have either initial terminal sign or later terminal sign.

Single loop circuit If all the elements of the circuit are connected in series then we call that a single loop circuit. We can apply Kirchhoff voltage Law and ohms law to find voltages and current of elements in the circuit.

Single node pair circuit In these type of circuit all the elements of circuit are connected between same pair of nodes. In other words we can say that all elements are in parallel. Therefore the voltage across all elements is the same.

Series and parallel connected sources Voltage sources are connected in series to get an equivalent voltage. Current sources are connected in parallel to get an equivalent current value.