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LECTURE NOTES
ON
BASIC ELECTRICAL ENGINEERING
II B. Tech I semester
COMPUTER SCIENCE AND ENGINEERING
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UNIT-I
Introduction to Electrical Engineering
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Ohms Law: At constant temperature potential difference across the conductor is directly proportional to
current flowing through the conductor is called ohms law.
V ∝I
V=IR
where the constant of proportionality R is called the resistance or electrical resistance, measured in
ohms (Ω). Graphically, the V − I relationship for a resistor according to Ohm‟s law is depicted in
Figure
Figure V − I relationship for a resistor according to Ohm‟s law.
At any given point in the above graph, the ratio of voltage to current is always constant
basic circuit components:
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Circuit Element
Voltage
Current
Resistor
V = IR
I=
Inductor
v=L
di
¸
0
R
i= 1
L
dt
v= 1
Capacitor
V
t
idt + v(0) C
i=C
¸
t
vdt
0
dv
, i = 0 for DC
dt
V − I relationships for a resistor, inductor and capacitor.
Kirchhoff’s Voltage Law (KVL)
Kirchhoff‟s Voltage Law states that the algebraic sum of voltages around each loop at any instant of time is
zero
Σ voltage drops = Σ voltage rises
Kirchhoff’s Current Law (KCL)
Kirchhoff‟s Current Law states that The algebraic sum of currents a node at any instant is zero.
Σ currents in = Σ currents out
Basic Definitions:
Current: the directed flow of electrons (charge) called current. It is denoted by I. units are Amps
Electrical potential: charged body capacity to do work is known as its electrical potential.
Potential difference: difference in potentials of two charged bodies is called Potential difference
Power: the rate at which an electrical work done in electrical work is called power. It is denoted by P. units are
Watt
Electrical work: Electrical work is said to be done when there is transfer of charge. It is denoted by W. units
are joules.
Energy: capacity to do work is called energy.
Electrical Network: A combination of various electric elements (Resistor, Inductor, Capacitor, Voltage source,
Current source) connected in any manner what so ever is called an electrical network
Classification of element:
We may classify circuit elements in two categories, passive and active elements.
Passive Element: The element which receives energy (or absorbs energy) and then either converts it into heat
(R) or stored it in an electric (C) or magnetic (L) field is called passive element.
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