Page 103 - Basic Electrical Engineering

For convenience, the nodes are labelled by latters.

For example in Fig. 2.1,

No. of nodes, N = 4 (i.e., A, B, C, D)

No. of branches, B = 5 (i.e., AB, BC, BD, CD, AD)
Independent meshes, M = B – N + 1

= 5 – 4 + 1 = 2 (i.e., ABDA, BCDB)

No. of loop = 3 (i.e., ABDA, BCDB and ABCDA). It is seen that a loop
ABCDA encloses two meshes, i.e., mesh 1 and mesh 2.

2.2.2 Voltage and Current Sources

A source is a device which converts mechanical, thermal, chemical or some

other form of energy into electrical energy. There are two types of sources:
voltage sources and current sources.

Voltage source

Voltage sources are further categorized as ideal voltage source and practical

voltage source. Examples of voltage sources are batteries, dynamos,
alternators, etc. Ideal voltage source is defined as the energy source which

gives constant voltage across its terminals irrespective of current drawn
through its terminals. The symbol of ideal voltage source is shown in Fig. 2.2

(a). In an ideal voltage source the terminal voltage is independent of the load
resistance, R connected. Whatever is the voltage of the source, the same
L
voltage is available across the load terminals of R , i.e., V = V under
L
L
S
loading condition as shown in Fig. 2.2 (b). There is no drop of voltage in the
source supplying current to the load. The internal resistance of the source is

therefore, zero.
In a practical voltage source, there will be a drop in voltage available
across the load due to voltage drop in the resistance of the source itself when