basic electrical engineering for students

Basic Electrical engineering

1. UNIT I DC & AC Circuits
DC Circuits: Electrical circuit elements (R, L and C), Ohm’s Law and its
limitations, KCL & KVL, series, parallel, series-parallel circuits, Super Position
theorem, Simple numerical problems.
AC Circuits: A.C. Fundamentals: Equation of AC Voltage and current, waveform,
time period, frequency, amplitude, phase, phase difference, average value, RMS
value, form factor, peak factor, Voltage and current relationship with phasor
diagrams in R, L, and C circuits, Concept of Impedance, Active power, reactive
power and apparent power, Concept of power factor (Simple Numerical problems).
Equipment Safety Measures: Working principle of Fuse and Miniature circuit
breaker (MCB), merits and demerits. Personal safety measures: Electric Shock,
Earthing phenomenon, Safety Precautions to avoid shock.

2. DC Circuits

3. Electrical Quantities

5. Sources
•Voltage source:
▪Energy source whose V is independent of I
▪V is independent of R
L
▪Source determines V and Load determines I
•Current source:
▪Energy source which delivers constant I
▪Independent of V
▪Source determines I and load determines V

6. Sources
6
•Source transformation:
•Combination of sources:

7. Components
•Resistance - R - Ohms()
•Inductance - L - Henrys (H)
•Capacitance - C - Farads (F)
•Energy received:
▪Dissipated as heat (R)
▪Stored in it as:
▪Magnetic field (L)
▪Electric field (C)
7

11. Resistance
•Ohms Law:
•Energy:
•Geometric:
▪where  = resistivity
•Series Combination: equal currents
•Parallel Combination: equal voltages
11IRV*= tRIW **
2
= A
L
R

= neq
RRRRR ...
321
+++= neq
RRRRR
1
....
1111
321
+++=
Series Combination
Parallel Combination

16. Inductance (L)
16
•Stores energy in magnetic field
•Influences only I is changed
•Property of opposing change in current
•If I remains constant, V = 0
•I cannot change instantaneously
• Energy:
•Geometric:
▪where  = 
0
r = permeability and 
0= 4x10
-7
H/mdt
di
LV= 2
2
1
LIW= l
AN
L
2

=

21. Capacitance (C)
21
•Stores energy in electric field
•Influences only when V is changed across its
terminals
•
•No I flows through a capacitor, if V remains
constant
•V across capacitor cannot change instantaneously
•Energy :
•Geometric:
▪where 
= 
0
r = permittivity and 
0 = 8.85x10
-12
F/mdt
dv
CI= 2
2
1
CVW= d
A
C

=

22. •Ohm’sLawstatesthattheamountofcurrentinacircuitis
proportionaltothevoltageacrossthecircuitandinversely
proportionaltotheresistanceinthatcircuit
•Voltage=CurrentxResistance
•The Limitations are:
1.Temperature conditions need to be constant
2.Not valid in unilateral elements (diode)
3.Not valid in Nonlinear elements (Opamp)
Ohm’s Law

23. Kirchhoff’s Current law
23
•Kirchhoff’s current law (KCL):
▪Algebraic sum of currents meeting at node is 0
▪Currents entering = Currents leaving0
1
=
=
n
i
i
I

24. Kirchhoff’s Voltage law
24
•Kirchhoff’s voltage law (KVL):
▪Algebraic sum of voltages across a loop is 0
▪Sources voltages = Loads voltages 0
1
=
=
n
i
i
V

25. Resistors in Series
•In series circuit resistors
are connected in chain
manner.
•Current flowing through
the given resistors is
always equal.
•Voltage is differ from
individual resistors
•Req= R1+R2+R3…Rn

28. Important Points:

29. Voltage Division Rule
Aseriescircuitactsasavoltagedividerasit
dividesthetotalsupplyvoltageintodifferent
voltagesacrossthecircuitelements.Figure2
showsavoltagedividercircuitinwhichthetotal
supplyvoltageVhasbeendividedinto
voltagesV
1andV
2acrosstwo
resistancesR
1andR
2.Although,thecurrent
throughbothresistancesissame,i.e.,I.

32. Problem

33. Resistors in parallel
•In parallel circuit heads
are connected together
and tails are connected
together.
•Current in parallel circuit
differ from individual
resistors.
•Voltage resistor is same
for all resistor.
•neq
RRRRR
1
....
1111
321
+++=

37. Important Points:

38. Current Division Rule

41. Problem

42. Series -Parallel

46. Problems of Series –Parallel Resistor

47. Draw the equivalent circuits for the below circuits and find
out the total current drawn from the supply.

48. •Determine the current (I3) flowing through
the 3Ω resistor in the below circuit.

49. Problems of Series –Parallel Resistor
Draw the equivalent circuits for the below circuits and find
out the total current drawn and current flowing through each
resistorfromthe supply.

52. Problems

66. Super Position theorem
•The superposition theorem states that a circuit with
multiple power sources can be analyzed by evaluating
only one power source at a time. Then, the component
voltages and currents are added algebraically to
determine the circuit response with all power sources
in effect.
•Step 1: Replace all of the power sources except one.
Replace voltage sources with a short circuit (wire) and
current sources with an open circuit (break).
•Step 2: Calculate the voltages and currents due to each
individual source.

67. Super Position theorem Cont..
•Step 3: Repeat steps 1 and 2 for each power supply.
•Step 4: Superimpose the individual voltages and
currents. Algebraically add the component voltages
and currents; paying particular attention to the
direction of the voltage drops and current flows.
Limitations:
•The superposition theorem is limited to use with linear,
bilateral circuits.
•The superposition theorem can be applied to DC, AC,
and combined AC/DC circuits.
•The superposition theorem cannot be used to add
power.

68. Problem
Find the Currents in R1 , R2 and R3 using Super position theorem ?

69. Step 1

70. Step 2

71. Step 3

72. Step 3

73. Step 4