Page 14 - Basics of Electrical, Electronic and Communication

2 Chapter 1. Basic Concepts in Electrical Engineering

Electromotive force
Energy is required for the movement of charge from one point to an-
other. In order to move electrons along a conductor, some amount of
work is required. The work required must be supplied by an electro-
motive force (emf) provided by a battery or a similar device.

Potential difference
Potential difference is the difference between the voltages at two ends
of a conductor.
A current carrying element is shown in figure 1.1. The voltage
across the element v ab is given by

W
V ab = (1.3)
Q
where work done (W) is measured in Joules and the charge (Q) in
Coulombs.

+ _
Element
a b
Vab

Figure 1.1: Potential drop across a current carrying element

The positive (+) and negative (-) signs shown on figure 1.1 define
the polarity of the voltage V ab . With this definition, V ab represents the
voltage at point a relative to point b. Equivalently we may also say that
the voltage at point a is V ab volts higher than the voltage at point b.

Electric circuit
An electric circuit is a closed connection formed by various electric
elements (Resistor, inductor, capacitor, voltage source, current source
etc.). The fundamental circuit model is shown in figure 1.2. The circuit
is made up of a source V S which provides a voltage across its terminals
and a resistor R L as load.

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