Nodes, Branches and Loops

Node is the point of connection between elements. Elements connected to the same nodes have the same voltage.

Branch: is the connection between two nodes. The elements in the same branch carry the same current.

Loop is the closed loops in the circuit diagram.

A network with b branches, n nodes, and l independent loops will satisfy the fundamental theorem of network topology:

Series Connection: Two or more elements are in series if they are connected sequentially and consequently carry the same current.

Parallel Connection: Two or more elements are in parallel if they are connected to the same two nodes and consequently have the same voltage across them.

Kirchhoff's Current Law

Algebraic sum of currents entering a closed loop (or a node) is zero.

Don't forget to use plus sign for current entering into node and negative sign for currents leaving the node if just the magnitudes are given.

Kirchhoff's Voltage Law

Algebraic sum of all voltages around a closed path (or loop) is zero.

If you meet with negative terminal of an element first, write that voltage as negative to the equation.