4th Semester
Basic Electronics
BASIC ELECTRONICS
Chapter 1
Circuit Fundamentals
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Circuit Fundamentals
Zero Reference Level
Ohm's Law
Linear and Non-Linear Resistor
Cell in Series and Parallel
Resistive Circuit
Series / Parallel Circuit &
Characteristics
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Kirchhoff's Law
Kirchhoff's Current Law
Kirchhoff's Voltage Law
Network Theorem
Superposition Theorem
Thevenin's Theorem
Norton's Theorem
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Session :
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Institute : ____________________________
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MRB NOTES
4th Semester
Basic Electronics
Basic Fundamentals
Electronics
-A branch of physics that deals with the emission, behavior, and effects of electrons (as in
electron tubes and transistors) and with electronic devices.
-The science dealing with development and application of devices and systems involving
the flow of electrons in semiconductors.
Current
-Current is the flow of electrical charges through an electronic circuit. The direction of
current is opposite to the direction of electron flow. Current is measured in AMPERES.
Conventional Current
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Conventional or Simple Current is due to
the flow of positive charges or holes from
the positive terminal to the negative
terminal.
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Means it flow from higher potential to
lower potential.
Electronic Current
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Electric or Electronic Current is due to the
flow of electrons from the negative
terminal to positive terminal.
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Means it flow from lower potential to
higher potential.
Voltage
-Voltage is the electrical force that causes current to flow in a circuit.
-Work done per unit charge from one point to another is also known as Voltage.
-Its unit is volts.
- ΔV=
W AB
q
Resistance
– Resistance is a measure of opposition to the current flow.
– It is measured in Ohms.
V
R=
–
I
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MRB NOTES
Basic Electronics
4th Semester
Circuit Fundamentals
Nodes, Branches, Loops and Meshes are the essential for the electric circuit analysis. These
elements are the fundamentals of the electric circuit. Electric circuit elements can be connected to
each other in various ways. Because of it, we need to understand the basic knowledge behind an
electric circuit such as network topology and circuit.
Network Topology
Network topology is a graphical representation of electrical circuits. It is useful for analyzing
complex electric circuit by converting them into network graphs. Network topology is also called as
Graph theory.
Circuit
A circuit is a network consisting of one or more closed paths.
Node
It is a connection point between two elements (such as resistor, inductor, capacitor etc) in a
circuit. Sometimes it is denoted as dots.
Branch
A part or section of a circuit which is located between two junctions is called Branch. In
other words, it may have any two element (terminal) with a single component such as a voltage
source, current source, resistor etc.
 Active element - That generated energy or produces energy such as AC source or batteries.
 Passive element - That uses energy or store energy such as Resistor.
Loop
It is closed path having same starting and ending points in a circuit. A loop can have multiple
meshes but a single mesh cannot contain a single loop.
Finding loops in a circuit
l=b–n+1
where
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l = Number of loops
b = Number of branches ( no. of elements )
n = Number of nodes
Mesh
It is a closed loop in which there is no other loop within it. Or any path that does not contain
any other path is called mesh.
In the given circuit there are 6 nodes ( dots ) ,
7 branches (6 Passive elements and 1 Passive element),
3 loops and 2 meshes.
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MRB NOTES
Basic Electronics
4th Semester
Zero Reference Level
In electronic circuits, we measure voltages at various points with respect to a common point
whose potential is considered to be zero. This common point of zero potential is called zero
reference level.
All circuit voltages whether positive or negative, are measured with respect to zero reference
level.
As shown in figure, the negative terminal of battery (point D ) is considered as zero
reference level.
Ohm's Law
The current flowing though a conductor is directly proportional to potential difference across
the ends provided the physical state (such as temperature etc.) of the conductor does not change.
Mathematical Form
The ohm's law can be expressed as
I V
1
I=
V
R
V = IR
Where R is the constant of proportionality and is called the resistance of conductor.
Resistance
Resistance is the measure of opposition to the current flow. It is measured in Ohms.
Ohm
Resistance is said to be one ohm, when one ampere current passes though the conductor due
to the potential difference of one volt.
1Volt
1Ohm =
1 Ampere
Dependence of Resistance of Conductor
Resistance of a conductor depends upon.
• Length and area of cross section.
• Physical state of conductor (temperature etc.)
• Nature of the conductor.
Ohmic Conductors
-A conductor, which obeys Ohm's law strictly, is called ohmic conductor.
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MRB NOTES
Basic Electronics
4th Semester
Examples of ohmic conductors
Matallic conductors are ohmic like copper, silver,gold etc.
Non-ohmic conductors
-A conductor which does not obey ohm's law is called non-ohmic conductor.
Examples of non-ohmic conductors
semiconductor diode, tungsten filament etc are non-ohmic .
Linear and Non-Linear Resistors
Resistors can be classified on various types based on various factors. Normally resistors can
be classified into two types namely linear resistor and non-linear resistor.
Linear Resistors
A linear resistor is the type of resistor whose resistance
remains constant with increase in the potential difference or voltage
applied to it.
The resistance or current passed through the resistor does not
change as the applied voltage (P.D) changes. The V-I characteristics
of such resistor is a straight line as shown in the figure or in other
words these types of resistor follow Ohm's law very strictly.
It is classified into two types
• Fixed Resistor
• Variable Resistor
Fixed Resistor
Fixed resistors are those type of resistors whose value is fixed already while manufacturing
and cannot be changed during it's usage.
Types of Fixed Resistors
• Wire Wound Resistors
• Thin Film Resistors
• Carbon Composition Resistors
Variable Resistor
Variable resistors are those types of resistors whose value can be changed during it's usage.
These types of resistor usually contains a shaft which can be rotated or moved by hand or a screw
driver to change its value in between a fixed range,
i.e. 0 kilo ohms to 20 kilo ohms.
Types of
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Variable Resistors
Potentiometer
Rheostat
Trimmer Resistor
MRB NOTES
Basic Electronics
4th Semester
Non-Linear Resistor
Non-Linear resistor are those type of resistor in which the
current passed though it is not exactly directly proportional to the
potential difference applied to it . These types of resistors have
non-linear V-I characteristics and does not strictly follows ohm's law.
It is classified into several types
• Thermistors
• Varistors
• Photo Resistor or LDR (Light Dependent Resistors)
• Surface Mount Resistor
Thermistors
The term is a combination of “thermal” and “resistor”. It is a type of variable resistor. It is a
device whose resistance is dependent on temperature. The resistance of a thermistor is inversely
proportional to the temperature.
Varistor
A varistor is an electronic component with an electrical resistance that varies with the applied
voltage. Also known as voltage-dependent resistor.
Cell in Series and Parallel
Cell
A cell or battery is the one which can convert chemical energy into electrical energy. A cell
consists of three parts.
Electrode- A positive terminal and negative terminal. The positive terminal of the cell is
called cathode and the negative terminal of the cell is called anode.
Electrolyte- A chemical solution.
Cell in Series circuit
➢ A series circuit is when the elements in a circuit are connected so that there is only a single
pathway for the current to flow. Or cells are joined end to end so that the same current flows
through each cell.
➢ The advantage of connecting cells in series is that it increases the electric potential (voltage)
produced at the output terminals of the batteries.
➢ As electron travels through the consecutive batteries, it gets an additional boost of energy
increasing its voltage.
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MRB NOTES
Basic Electronics
4th Semester
Cell in Parallel circuit
➢ A parallel circuit is when the element in a circuit are connected in such a way that there is
more than one pathway for the current to flow.
➢ The cells are connected side by side or in parallel to increase the electric change.
➢ The electrons flow through only one cell before passing though the load (resistor).
➢ Therefore, the electric potential (voltage) of the electron remains the same as if there were
only one cell in the circuit.
➢ But the duration of the time, the load will operate is directly related to the number of cells in
the circuit.
Resistive Circuit
An electric circuit that contains just a pure resistance is called resistive circuit. In a completely
resistive circuit, inductance and capacitance do not exist. In both directions of the circuit, the
alternating current and voltage go forward and backward. As a result, the alternating current and
voltage take on the shape of a Sine wave or sinusoidal waveform.
Series / Parallel Circuits and Characteristics
Series Circuit
Two or more elements are said to be in series if they share a single node and carry the same
current.
Characteristics
➢ There is only one path for current to flow though the circuit. This means current is same
everywhere in the circuit.
➢ Each component has an individual Ohm's law Voltage drop. This means we can calculate
voltage using Ohm's law if we know Current and Resistance.
➢ Kirchoff's Voltage Law Applies. This means that the sum of all the voltage sources is equal
to the sum of all the voltage drops or
VT = V1 + V2 + V3 + ...+ VN
➢ The total resistance in the circuit is equal to the sum of individual resistances.
Req = R1 + R2 + R3 +...+ RN
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MRB NOTES
Basic Electronics
4th Semester
Parallel Circuit
Two or more elements are said to be in parallel if they are connected to the same two nodes
and carry the same voltage across them.
Characteristics
➢ The voltage in each component is the same everywhere in the circuit.
➢ Each branch has individual current path. This means we can calculate current using Ohm's
law if we know voltage across the component and resistance.
➢ Kirchoff' Current Law Applies. This means that the sum of all the voltage sources is equal to
the sum of all the voltage drops or
IT = I1 + I2 + I3 +...+ IN
➢ Total resistance in the circuit is equal to inverse the sum of the inverse of the individual
resistances.
1
1
1
1
1
= + + +...+
Req R 1 R2 R3
RN
➢
Kirchhoff's Laws
Kirchhoff's Circuit Law
Sometimes in complex circuits such as bridge or T networks, we can not use simply ohm's
law to find current and voltage, in those circuits we apply Kirchhoff's Circuit Law.
In 1845, a German physicist, Gustav Kirchoff developed a pair or set of rules or laws which
deal with the conservation of current and energy within Electrical Circuits. These two rules are
commonly known as: Kirchhoff's Current Law, (KCL) dealing with the current flowing around a
closed circuit, while the other law deals with the voltage sources present in a closed circuit, known
as Kirchhoff's Voltage Law, (KVL).
Kirchhoff's First Law – The Current Law, (KCL)
“The Total current or charge entering a junction or node is exactly equal to the charge
leaving the node as it has no other place to go except to leave, as no charge is lost within the
node“.
In other words the algebraic sum of ALL the currents entering and leaving a node must be
equal to zero.
I(exiting) + I(entering) = 0.
This idea by Kirchhoff's is commonly known as the Conservation of Charge.
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MRB NOTES
Basic Electronics
4th Semester
Kirchhoff's Current Law
Here, the 3 currents entering the node, I1, I2, I3 are all positive in value and the 2 currents
leaving the node, I4 and I5 are negative in value. Then this means we can also rewrite the equation
as;
I1 + I2 + I3 – I4 – I5 = 0
Kirchhoff's Second Law – The Voltage Law, (KVL)
“In any closed loop network, the total voltage around the loop is equal to the sum of all the
voltage drops within the same loop which is also equal to zero.”
In other words the algebraic sum of all voltages within the loop must be equal to zero.
This idea by Kirchoff is known as the Conservation of Energy.
V1 + V2 + V3 + … = 0
Kirchhoff's Voltage Law
Starting at any point in the loop continue in the same direction noting the direction of all the
voltage drops, either positive or negative, and returning back to the same starting point. It is
important to maintain the same direction either clockwise or anti-clockwise or the final voltage sum
will not be equal to zero. We can use Kirchhoff’s voltage law when analyzing series circuits.
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MRB NOTES
Basic Electronics
4th Semester
Network Theorem
Electric circuit theorems are always beneficial to help find voltage and currents in multi-loop
circuits. These theorems use fundamental rules or formulas and basic equations of mathematics to
analyze basic components of the electrical or electronics parameters such as voltage, current,
resistance, and so on. These fundamental theorems include the basic theorems like Superposition
theorem, Thevenin's theorem, Norton's theorem etc.
Superposition Theorem
Statement
“The voltage across the source, or current through an element in a linear circuit
is the algebraic sum of voltage across, or current through an element due to each independent
source acting alone.”
Step to apply Superposition Theorem :
1) Turn off all independent sources except one source. Find the output (voltage or current) due
to the active source using the techniques.
2) Repeat step 1) for each of the other independent sources.
3) Find the total contribution by adding algebraically all the contributions due to the
independent sources.
Disadvantage
Analyzing a circuit using superposition has one major disadvantage:
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It may very likely involved more work.
If the circuit has three independent sources, we may have to analyze three simpler
circuits each providing the contribution due to the respective individual source.
Advantage
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Superposition does help reduce a complex circuit to simpler circuits though replacement of
voltage sources by short circuits and of current sources by open circuits.
Example 1 : For the given circuit shown, find the current in all
branches , using Superposition theorem.
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MRB NOTES
4th Semester
Basic Electronics
1. Consider 6 volt only , replaced 12 volt source by its internal
resistance .
3×6
+ 0.5 = 5 Ω
3+6
R t = 2.5 +
'
I1 =
Vt
6
=
= 1.2 A
5
RT
Using C.D.R :
'
I2 =
I '2 =
6
6+3
6
1.2×
= 0.8 A
9
I 1×
I ' = I '1 - I '2 = 1.2 – 0.8 = 0.4
2. Consider 12 volt only , replaced 6 volt source by its internal
resistance .
R t=2+
I '2' =
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3×6
+1=5Ω
3+6
Vt
=
RT
12
= 2.4 A←
5
MRB NOTES
4th Semester
Basic Electronics
Using C.D.R :
I '1' = I 2 ×
6
6+3
I '1' = 2.4 ×
6
= 1.6 A ←
9
I ' ' = I '2'
-
I '1' = 2.4 – 1.6 = 0.8 A
↓
Now, take 6 volt and 12 volt sources in consideration :
'
''
I = I + I = 0.4 + 0.8 = 1.2 A ↓
''
I1 = I1
-
''
I2 = I2
-
I 1 = 1.6 – 1.2 = 0.4 A←
'
I '2 = 2.4 - 0.8 = 1.6 A←
Example 2 : For the given circuit, find the current flows through 10 Ω resistor, using
superposition theorem.
1. Consider 50 volt source only, replace 2 A current source by open circuit.
Rt = 2 +
I1 =
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6×15
= 6.285 Ω
6+15
Vt
=
RT
50
= 7.955 A
6.285
MRB NOTES
4th Semester
Basic Electronics
Using C.D.R :
I 3 = I 1×
6
6+15
I 3 = 7.955×
6
= 2.272 A →
21
2. Consider 2 A current source only, replaced 50 volt source by short circuit.
2×6
+ 10 = 11.5 Ω
2+6
It is clear that 11.5 Ω|| 5 Ω
Using C.D.R :
I '3 = 2×
5
= 0.606 A←
11.5
I 10Ω = I 3
-
I '3 = 2.272 – 0.606 = 1.66 A →
Thevenin's Theorem
Statement
“A linear (Two terminal) circuit can be replaced by an equivalent circuit consisting of
voltage source VTh in series with a resistor RTh, VTh is the open circuit voltage at the terminals
and where RTh is input resistor or equivalent resistance at the terminals when all the
independent sources are turn off.”
In order to find Thevenin's equivalent circuit we have steps to consider:
1. Turn off sources (Current or Voltage source). Short the voltage source, open the current
source.
2. Make an open circuit.
3. Determine RTh
4. Turn on sources and solve for VTh
5. Draw for Thevenin's equivalent circuit.
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Basic Electronics
4th Semester
Norton's Theorem
Statement
“A linear circuit ( two terminal) can be replaced by an equivalent circuit consisting of a
current source IN parallel with a resistor RN, where IN is the short circuit current through the
terminals and RN is the input or equivalent resistance at the terminals when the independent
sources are turn off.”
Norton Resistance RN :
We find RN in the same way we find RTh. In fact what we know about source transformation,
the Thevenin's and Norton resistance are equal.
RN = RTh
Norton Current IN :
We determine the short-circuit current flowing from terminal a to b in both circuits above. It
is evident that the short-circuit current in figure b in IN. This must be same short-circuit current from
terminal a to b in figure a. Since the two circuits are equivalent. Thus
IN = ISC
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Basic Electronics
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Basic Electronics
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