1
Basic Electrical and Electronics Engineering
Course Code: ESC-201
Semester- II
Faculty: Dr. Sarabdeep Singh
Model Institute of
Engineering & Technology
Course Details
Section-A
Unit 1: Elementary Concepts of DC and AC Circuits: Recent
advancements in Electrical Engineering, DC Circuit elements (R,
L and C), Voltage and Current sources, Kirchhoff’s Current and
Voltage laws, mesh and nodal analysis. Superposition, Maximum
power transfer, Thevenin and Norton theorems.
Course Outcomes
Course Description Mapping with
Outcomes Program
Outcomes
CO1 Apply fundamental concepts to solve simple DC and 1,2,3,4,6
AC electric circuits.
CO2 Examine sinusoidal waveforms and classify measuring 1,2,3,4,6
instruments
CO3 Explain the construction and principle of operation of 1,2,3,4,6
single phase transformers and DC Machines.
CO4 Understand the characteristics of semiconductor devices 1,2,3,4,6
and rectifier circuits.
CO5 Interpret the principle of various transistor configurations 1,2,3,4,6
and characteristics.
Assessment and Evaluation Plan
Assessment Tools Evaluation
◻ Assignment ◻ 20 marks
◻ Sessional ◻ 20 marks
◻ Attendance ◻ 10 marks
◻ External Exam ◻ 100 marks
Outcomes of Today’s Lecture
◻ Understand the Concepts of DC and AC Circuits
◻ Articulate the Recent advancements in Electrical Engineering
◻ Learn about the DC Circuit elements (R, L and C)
◻ Understanding about Voltage and Current sources
Concept of DC and AC Current
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◻ Both AC and DC describe types of current flow in a circuit.
◻ In direct current (DC), the electric charge (current) only flows in
one direction.
◻ Electric charge in alternating current (AC), on the other hand,
changes direction periodically. The voltage in AC circuits also
periodically reverses because the current changes direction.
Comparison of DC and AC Current
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DC Circuits
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❑ The closed path in which the direct current flows is called the
DC circuit. The current flows in only one direction and it is
mostly used in low voltage applications. The resistor is the
main component of the DC circuit.
DC Circuits
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◻ A D.C. circuit essentially consists of a source of D.C. power (e.g. battery,
D.C. generator etc.), the conductors used to carry current and the load.
Figure below shows a bulb connected to a battery through conducting
wires. The direct current starts from the positive terminal of the battery
and comes back to the starting point via the load. The direct current
follows the path ABCDA and ABCDA is a D.C. circuit.
Types of DC Circuits
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◻ The DC electric circuit is mainly classified into three groups. They are :
1. Series circuit,
2. Parallel circuit, and
3. Combination of series and parallel circuit.
Types of DC Circuits
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DC Series Circuit
◻ The circuit which has DC series source, and the number of resistors are
connected end to end so that same current flows through them is called a DC
series circuit. The figure below shows the simple series circuit. In the series
circuit the resistor R1, R2, and R3 are connected in series across a supply voltage
of V volts. The same current I is flowing through all the three resistors.
I I
DC Series Circuit
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If V1, V2, and V3 are the voltage drops across the three resistor R 1, R2, and
R3 respectively, then
Let R be the total resistance of the circuit then,
Total resistance = Sum of the individual resistance.
In such type of circuit all the lamps are controlled by the single switch and they
cannot be controlled individually. The most common application of this circuit is for
decoration purpose where a number of low voltage lamps are connected in series.
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Problem: Two filament lamps A and B take 0.8 A and 0.9 A respectively
when connected across 110 V supply. Calculate the value of current when
they are connected in series across a 220-V supply, assuming the filament
resistances to remain unaltered. Also find the voltage across each lamp.
Solution:
For lamp A, RA = 110/0.8 = 137.5 Ω
For lamp B, RB = 110/0.9 = 122.2 Ω
When the lamps are connected in series, total resistance is
RS = 137.5 + 122.2 = 259.7 Ω
Circuit current, I = V/RS = 220/259.7 = 0.847 A
Voltage across lamp A = I RA = 0.847 × 137.5 = 116.5 V
Voltage across lamp B = I RB = 0.847 × 122.2 = 103.5 V
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Problem: Two filament lamps A and B having resistances RA =137.5 Ω, and RB =
122.2 Ω. Calculate the value of current when they are connected in series across a
220-V supply. Also find the voltage across each lamp.
Solution:
When the lamps are connected in series, total resistance is
RS = 137.5 + 122.2 = 259.7 Ω
Circuit current, I = V/RS = 220/259.7 = 0.847 A
Voltage across lamp A = I RA = 0.847 × 137.5 = 116.5 V
Voltage across lamp B = I RB = 0.847 × 122.2 = 103.5 V
DC Parallel Circuit
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The circuit which have DC source and one end of all the resistors is joined to a
common point and other end are also joined to another common point so that current
flows through them is called a DC parallel circuit.
The figure shows a simple parallel circuit. In this circuit the three resistor
R1, R2, and R3 are connected in parallel across a supply voltage of V volts. The
current flowing through them is I1, I2 and I3 respectively.
DC Parallel Circuit
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The total current drawn by the circuit:
Let R be the total or effective resistance of the circuit, then
Reciprocal of total resistance = sum of reciprocal of the individual resistance..
All the resistance is operated to the same voltage, therefore all of them are connected
in parallel. Each of them can be controlled individually with the help of a separate
switch.
DC Parallel Circuit
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◻ Problem: 3 resistors 4, 12 and 6 ohm are connected in parallel. If
the total current taken is 12A, Find the current through each
resistor.
◻ Solution:
DC Series-Parallel Circuit
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The circuit in which series and parallel circuit are connected in series is
called a series-parallel circuit. The figure below show the series-parallel
circuit. In this circuit, two resistor R1 and R2 are connected in parallel with
each other across terminal AB. The other three resistors R 3, R4 and R6 are
connected in parallel with each other across terminal BC.
DC Series-Parallel Circuit
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The two groups of resistor RAB and RBC are connected in series with
each other across the supply voltage of V volts. The total or
effective resistance of the whole circuit can be determined as given
below
Alternating Voltage and Current in an AC Circuit
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◻ The voltage that changes its polarity and magnitude at regular interval of time is
called an alternating voltage. Similarly, the direction of the current is changed
and the magnitude of current changes with time it is called alternating current.
◻ When an alternating voltage source is connected across a load resistance as
shown in the figure below, the current through it flows in one direction and then
in the opposite direction when the polarity is reversed.
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Alternating Voltage and Current in an AC Circuit
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◻ The waveform of the alternating voltage with respect to the time and the
current flowing through the resistance (R) in the circuit is shown below.
AC Circuit
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◻ The circuit that is excited using alternating source is called an AC Circuit. The
alternating current (AC) is used for domestic and industrial purposes. In an AC
circuit, the value of the magnitude and the direction of current and voltages is not
constant, it changes at a regular interval of time.
◻ It travels as a sinusoidal wave completing one cycle as half positive and half
negative cycle and is a function of time (t) or angle (θ=wt).
◻ In DC Circuit, the opposition to the flow of current is the only resistance of the
circuit whereas the opposition to the flow of current in the AC circuit is because
of resistance (R), Inductive Reactance (X L=2πfL) and capacitive reactance (XC =
1/2 πfC) of the circuit.
◻ In AC Circuit, the current and voltages are represented by magnitude and
direction. The alternating quantity may or may not be in phase with each other
depending upon the various parameters of the circuit like resistance, inductance,
and capacitance. The sinusoidal alternating quantities are voltage and current
which varies according to the sine of angle θ.
AC Circuit
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◻ There are various types of AC circuit such as AC circuit containing only
resistance (R), AC circuit containing only capacitance (C), AC circuit containing
only inductance (L), the combination of RL Circuit, AC circuit containing
resistance and capacitance (RC), AC circuit containing inductance and
capacitance (LC) and resistance inductance and capacitance (RLC) AC circuit.
◻ The various terms which are frequently used in an AC circuit are as follows
◻ Amplitude
The maximum positive or negative value attained by an alternating quantity in one complete
cycle is called Amplitude or peak value or maximum value. The maximum value of voltage and
current is represented by Em or Vm and Im respectively.
AC Circuit
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◻ Alternation
One-half cycle is termed as alternation. An alternation span is of 180 degrees electrical.
◻ Cycle
When one set of positive and negative values completes by an alternating quantity or it goes through
360 degrees electrical, it is said to have one complete Cycle.
◻ Instantaneous Value
The value of voltage or current at any instant of time is called an instantaneous value. It is denoted by
(i or e).
◻ Frequency
The number of cycles made per second by an alternating quantity is called frequency. It is measured
in cycle per second (c/s) or hertz (Hz) and is denoted by (f).
◻ Time Period
The time taken in seconds by a voltage or a current to complete one cycle is called Time Period. It is
denoted by (T).
◻ Wave Form
The shape obtained by plotting the instantaneous values of an alternating quantity such as voltage and
current along the y-axis and the time (t) or angle (θ=wt) along the x-axis is called a waveform.
Voltage Sources
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A source is a device that converts mechanical, thermal, chemical, or some other form of
energy into electrical energy. There are two types of sources: voltage source and current
source.
Voltage Source:
◻ A voltage source is a two-terminal device which can maintain a fixed voltage across
its terminals. An ideal voltage source can maintain the fixed voltage independent of
the load resistance or the output current. However, a real-world voltage source cannot
supply unlimited current.
◻ Examples of voltage sources are batteries, dynamos, alternators, etc.
◻ If the voltage across an ideal voltage source can be specified independently of any
other variable in a circuit, it is called an independent voltage source.
◻ If the voltage across an ideal voltage source is determined by some other voltage or
current in a circuit, it is called a dependent or controlled voltage source.
Voltage Sources
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◻ The internal resistance of an ideal voltage source is zero.
◻ It is able to supply or absorb any amount of current. The current through an
ideal voltage source is completely determined by the external circuit.
◻ When connected to an open circuit, there is zero current and thus zero power.
◻ When connected to a load resistance, the current through the source
approaches infinity as the load resistance approaches zero (a short circuit).
Thus, an ideal voltage source can supply unlimited power.
Voltage Sources
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Voltage Source
◻ Voltage sources are further categorized as ideal voltage source and practical voltage source.
◻ An ideal voltage source is defined as the energy source that gives constant voltage across
its terminals irrespective of current drawn through its terminals. The symbol of ideal
voltage source is shown in Figure 1(a).
◻ In an ideal voltage source, the terminal voltage is independent of the value of the load
resistance (RL) connected. Whatever is the voltage of the source, the same voltage is
available across the load terminals of RL, that is, VL = VS under loading condition as shown
in Figure 1(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, voltage across the load will be less than the source voltage
due to voltage drop in the resistance of the source itself when a load is connected, as shown
in Figure 1(c).
Voltage Sources
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Figure 1 Voltage source and its characteristics: a) symbol, b) circuit and c)
load characteristics.
Current source
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◻ In certain applications, a constant current flow through the circuit is
required. When the load resistance is connected between the output
terminals, a constant current (IL) will flow through the load.
◻ A current source is an electronic circuit that delivers or absorbs
an electric current which is independent of the voltage across it.
◻ A current source is the dual of a voltage source. The term current sink is
sometimes used for sources fed from a negative voltage supply. The
symbol of current source is shown in Figure
◻ Figure 2
Current source
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◻ Some examples of current source are photoelectric cells, collector
current in transistors, etc.
◻ Figure 1 shows the schematic symbol for an ideal current source
driving a resistive load.
Current source
Chap 1 -
32
There are two types of current sources;
◻ An independent current source (or sink) delivers a
constant current.
◻ A dependent current source delivers a current which
is proportional to some other voltage or current in
the circuit
Comparison between Voltage and Current sources
Chap 1 -
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Voltage source
◻ Mostly sources of electrical power like battery are known as a voltage
source.
◻ In case of open circuitry, the ideal source delivers no power, in case of
short circuitry it gives infinite power.
◻ This ideal device has the 0-ohm internal resistance but the practical
source has less value of inner resistance but not zero.
Current Source
◻ The current source delivers the non-variable current when the connected
load has less value of resistance.
◻ In the case of the short circuitry, the ideal source delivers the no power,
but in case of open circuit, its power value becomes infinity.
◻ The ideal source has infinite resistance value and the practical source has
high but in some limit value of the resistance.
Voltage Sources
Chap 1 -
34
A source is a device that converts mechanical, thermal, chemical, or some other form of
energy into electrical energy. There are two types of sources: voltage source and current
source.
Voltage Source:
◻ A voltage source is a two-terminal device which can maintain a fixed voltage across
its terminals. An ideal voltage source can maintain the fixed voltage independent of
the load resistance or the output current. However, a real-world voltage source cannot
supply unlimited current.
◻ Examples of voltage sources are batteries, dynamos, alternators, etc.
◻ If the voltage across an ideal voltage source can be specified independently of any
other variable in a circuit, it is called an independent voltage source.
◻ If the voltage across an ideal voltage source is determined by some other voltage or
current in a circuit, it is called a dependent or controlled voltage source.
Voltage Sources
Chap 1 -
35
◻ The internal resistance of an ideal voltage source is zero.
◻ It is able to supply or absorb any amount of current. The current through an
ideal voltage source is completely determined by the external circuit.
◻ When connected to an open circuit, there is zero current and thus zero power.
◻ When connected to a load resistance, the current through the source approaches
infinity as the load resistance approaches zero (a short circuit). Thus, an ideal
voltage source can supply unlimited power.
Voltage Sources
Chap 1 -
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Voltage Source
◻ Voltage sources are further categorized as ideal voltage source and practical voltage source.
◻ An ideal voltage source is defined as the energy source that gives constant voltage across its
terminals irrespective of current drawn through its terminals. The symbol of ideal voltage
source is shown in Figure 1(a).
◻ In an ideal voltage source, the terminal voltage is independent of the value of the load
resistance (RL) connected. Whatever is the voltage of the source, the same voltage is
available across the load terminals of RL, that is, VL = VS under loading condition as shown
in Figure 1(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, voltage across the load will be less than the source voltage due
to voltage drop in the resistance of the source itself when a load is connected, as shown in
Figure 1(c).
Voltage Sources
Chap 1 -
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Figure 1 Voltage source and its characteristics: a) symbol, b) circuit and c)
load characteristics.
Current source
Chap 1 -
38
◻ In certain applications, a constant current flow through the circuit is
required. When the load resistance is connected between the output
terminals, a constant current (IL) will flow through the load.
◻ A current source is an electronic circuit that delivers or absorbs
an electric current which is independent of the voltage across it.
◻ A current source is the dual of a voltage source. The term current sink is
sometimes used for sources fed from a negative voltage supply. The
symbol of current source is shown in Figure
◻ Figure 2
Current source
◻ Some examples of current source are photoelectric
cells, collector current in transistors, etc.
There are two types of current sources;
◻ An independent current source (or sink) delivers a
constant current.
◻ A dependent current source delivers a current which
is proportional to some other voltage or current in the
circuit
Chap 1 - 39
Comparison between Voltage and Current sources
Chap 1 -
40
Voltage source
◻ Mostly sources of electrical power like battery are known as a voltage
source.
◻ In case of open circuitry, the ideal source delivers no power, in case of
short circuitry it gives infinite power.
◻ This ideal device has the 0-ohm internal resistance but the practical source
has less value of inner resistance but not zero.
Current Source
◻ The current source delivers the non-variable current when the connected
load has less value of resistance.
◻ In the case of the short circuitry, the ideal source delivers the no power,
but in case of open circuit, its power value becomes infinity.
◻ The ideal source has infinite resistance value and the practical source has
high but in some limit value of the resistance.
