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APJ Abdul Kalam Technological University
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EC201
NETWORK
THEORY
NOTE

UNIT I BASIC CIRCUIT ANALYSIS 12
Ohm‟s law, Kirchoff‟s laws – DC and AC circuits –
Resistors in series and parallel circuits – Mesh current and
node voltage method of analysis for DC and AC circuits ( AC
circuits at elementary level only)
The terms which are used frequently in circuit analysis :
Circuit - a circuit is a closed loop conducting path in which an
electrical current flows.
Path - a line of connecting elements or sources with no elements or
sources included more than once.
Node - a node is a junction, connection or terminal within a circuit
were two or more circuit elements are connected or joined together giving a
connection point between two or more branches. A node is indicated by a dot.
Branch - a branch is a single or group of components such as
resistors or a source which are connected between two nodes.
Loop - a loop is a simple closed path in a circuit in which no
circuit element or node is encountered more than once.
Mesh - a mesh is a single open loop that does not have a closed
path. No components are inside a mesh.
Components are connected in series if they carry the same current.
Components are connected in parallel if the same voltage is across
them.

Kirchoff's Law
Kirchoff's First Law - The Current Law, (KCL)
"The total current or charge entering a junction or node is exactly equal to
the charge leaving the node as it has no other place to go except to leave, as no charge is
lost within the node".
In other words the algebraic sum of ALL the currents entering and leaving a node
must be equal to zero,
I(exiting) + I(entering) = 0.
This idea by Kirchoff is known as the Conservation of Charge.
Here, the 3 currents entering the node, I1, I2, I3 are all positive in value and the 2
currents leaving the node, I4 and I5 are negative in value.
Then this means we can also rewrite the equation as;
I1 + I2 + I3 - I4 - I5 = 0

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