CIT-134 Electronics I

CIT-134 Electronics I
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TABLE OF CONTENT
Labs Experiments Sign
Lab #1 Study of Ammeter, Voltmeter and Multimeter
Measurement of current, voltage and resistance

Lab #2
Verification of Ohm's Law by Voltage and Resistance Constant.
Verify the laws of series and parallel combination of

Lab #3
resistances by ohms method
Lab #4 Determine temperature coefficient of resistance
Lab #5 Verify Kirchhoffs' laws
Lab #6 Practice of resistor colour coding
Lab #7 Combine cells in series and parallel and verify the net voltage
Study of lead acid battery, practice and use of hydrometer and

Lab #8
electrolyte preparation
Lab #9 Study of various types of capacitors and their colour coding.
Lab #10 Verify laws of combination of capacitors
Lab #11 Observe capacitor charging and discharging
Determine of wave length, time period and frequency of a given

Lab #12
AC signal by oscilloscope
Lab #13 Study the behavior of inductance and capacitance with AC and
DC supplies.
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Lab #14 Draw the forward & reverse characteristics of a P.N. junction
diode
Assemble a half wave diode rectifier circuit and observe its input
Lab #15
and out put waveforms
Assemble a full wave diode rectifier circuit and observe its input
Lab #16
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Practical No 1
Object: Study of Ammeter, Voltmeter and Multimeter.
Theory:
What is an Ammeter?
An ammeter (abbreviation of Ampere meter) is a measuring instrument used to measure the current
in a circuit. Electric currents are measured in
amperes (A), hence the name. The ammeter is
usually connected in series with the circuit in
which the current is to be measured. An
ammeter usually has low resistance so that it
does not cause a significant voltage drop in the
circuit being measured.
Instruments used to measure smaller currents,
in the milliampere or microampere range, are
designated as milliammeters or
microammeters. Early ammeters were laboratory instruments that relied on the Earth's magnetic
field for operation. By the late 19th century, improved instruments were designed which could be
mounted in any position and allowed accurate measurements in electric power systems. It is
generally represented by letter 'A' in a circuit.
What is Voltmeter?
A voltmeter is an instrument used for
measuring electric potential difference
between two points in an electric circuit. It
is connected in parallel. It usually has a high
resistance so that it takes negligible current
from the circuit.
Analog voltmeters move a pointer across a
scale in proportion to the voltage measured and can be built from a galvanometer and series
resistor. Meters using amplifiers can measure tiny voltages of microvolts or less. Digital voltmeters
give a numerical display of voltage by use of an analog-to-digital converter.
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What is Multimer?
A multimeter is a measuring instrument that can measure
multiple electrical properties. A typical multimeter can
measure voltage, resistance, and current, in which case it is
also known as a volt-ohm-milliammeter (VOM), as the unit
is equipped with voltmeter, ammeter, and ohmmeter
functionality. Some feature the measurement of additional
properties such as temperature and capacitance.
Analog multimeters use a microammeter with a moving
pointer to display readings. Digital multimeters (DMM,
DVOM) have numeric displays and have made analog
multimeters virtually obsolete as they are cheaper, more
precise, and more physically robust than analog multimeters.
Result: We have Studied the Ammeter , Voltmeter and Multimeter.

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Practical No 2
Object:
a) Measurement of current, voltage and resistance.
b) Verification of Ohm's Law by:
Keeping the voltage constant.
Keeping the resistance constant..
Theory :
Measuring of Current Voltage and Resistance?
The most commonly used piece of equipment for electrical measurements is the multimeter,
which is capable of measuring current (amps), voltage (volts) and resistance (ohms). There are
two basic type of multimeter - analogue and digital. Each has advantages and disadvantages,
depending upon the type of measurement being taken. Examples of both are shown below:
The voltage across a component is a measure of the difference in electrical potential from one
side of the component to the other and so the meter must be attached as shown:
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Current is a measure of the rate of flow of electrons through the circuit. To measure the flow of
current, the circuit must be broken and the meter must be placed in the circuit such that the
current flow goes through it. This is shown below:
In order to measure resistance, the component must first be removed from the circuit. This is to
ensure that the other components in the circuit do not affect the reading. The meter probes are
then connected either side of the component as shown:
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Verifying OHMS Law by Voltage and Resistance Constant

Ohm's law states that the current I through a conductor is proportional to the voltage V across its
ends. It is written as V=IR, where R is the resistance of the conductor.
Experiment to Verify Ohm's Law

Ohm's law can be easily verified in the lab or at home. You need a voltmeter, an ammeter, power
supply (dry cells), resistors, and connecting wires. A simple procedure to verify Ohm's law is
given below:
Mathematically, this current-voltage relationship is written as,
V=IR
In the equation, the constant of proportionality, R, is called Resistance and has units of ohms,
with the symbol Ω.
The same formula can be rewritten in order to calculate the current and resistance respectively as
follows:
𝐕 𝐕
I= R=
𝐑 𝐈
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Result:
We have Verified the OHMS law by Voltage and Resistance Constant.
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Practical No 3
Object: Verify the laws of series and parallel combination of
resistances by i) Ohmmeter method.
ii) Voltmeter-Ammeter method.
Theory:
Resistors in Series
Resistors are said to be in series whenever the current flows through the resistors sequentially.
Consider Figure which shows three resistors in series with an applied voltage equal to V_{ab}.
Since there is only one path for the charges to flow through, the current is the same through each
resistor. The equivalent resistance of a set of resistors in a series connection is equal to the
algebraic sum of the individual resistances.
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In Figure the current coming from the voltage source flows through each resistor, so the current
through each resistor is the same. The current through the circuit depends on the voltage supplied
by the voltage source and the resistance of the resistors. For each resistor, a potential drop occurs
that is equal to the loss of electric potential energy as a current travels through each resistor.
According to Ohm’s law, the potential drop V across a resistor when a current flows through it is
calculated using the equation V=IR, where I is the current in amps and R is the resistance in
ohms . Since energy is conserved, and the voltage is equal to the potential energy per charge, the
sum of the voltage applied to the circuit by the source and the potential drops across the
individual resistors around a loop should be equal to zero:
This equation is often referred to as Kirchhoff’s loop law, which we will look at in more detail
later in this chapter. For Figure 6.2.2, the sum of the potential drop of each resistor and the
voltage supplied by the voltage source should equal zero:
For the simple 1-bit subtraction problem above, if the borrow bit is ignored the result of their
binary subtraction resembles that of an Exclusive-OR Gate. To prevent any confusion in this
tutorial between a binary subtractor input labelled, B and the resulting borrow bit output from the
binary subtractor also being labelled, B, we will label the two input bits as X for the minuend and
Y for the subtrahend. Then the resulting truth table is the difference between the two input bits of
a single binary subtractor is given as:
Since the current through each component is the same, the equality can be simplified to an
equivalent resistance, which is just the sum of the resistances of the individual resistors.
Any number of resistors can be connected in series. If N resistors are connected in series, the
equivalent resistance is
Equivalent Resistance, Current, and Power in a Series Circuit

A battery with a terminal voltage of 9~\mathrm{V} is connected to a circuit consisting of four
20ohms 10ohms resistors all in series (Figure 6.2.3). Assume the battery has negligible internal
resistance. (a) Calculate the equivalent resistance of the circuit. (b) Calculate the current through
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each resistor. (c) Calculate the potential drop across each resistor. (d) Determine the total power
dissipated by the resistors and the power supplied by the battery.
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Resistors in Parallel
In Figure shows resistors in parallel, wired to a voltage source. Resistors are in parallel when one
end of all the resistors are connected by a continuous wire of negligible resistance and the other
end of all the resistors are also connected to one another through a continuous wire of negligible
resistance. The potential drop across each resistor is the same. Current through each resistor can
be found using Ohm’s law I=V/R, where the voltage is constant across each resistor. For
example, an automobile’s headlights, radio, and other systems are wired in parallel, so that each
subsystem utilizes the full voltage of the source and can operate completely independently. The
same is true of the wiring in your house or any building.
The current flowing from the voltage source in Figure depends on the voltage supplied by the
voltage source and the equivalent resistance of the circuit. In this case, the current flows from the
voltage source and enters a junction, or node, where the circuit splits flowing through resistors
R1 and R2. As the charges flow from the battery, some go through resistor R1 and some flow
through resistor R2. The sum of the currents flowing into a junction must be equal to the sum of
the currents flowing out of the junction:
This equation is referred to as Kirchhoff’s junction rule and will be discussed in detail in the next
section. In Figure 6.2.4, the junction rule gives I=I1+ I2. There are two loops in this circuit,
which leads to the equations V=I1 R1 and I1 R1=I2 R2 Note the voltage across the resistors in
parallel are the same (V=V1=V2) and the current is additive:
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Result: We have verified the law of series and parallel combination through ohms and
voltmeter and ammeter method.
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Practical No 4
Object: Determine temperature coefficient of resistance..
Theory:
Temperature coefficient of resistance
The temperature coefficient of resistance measures changes in the electrical resistance of any
substance per degree of temperature change.
Let us take a conductor having a resistance of R0 at 0oC and Rt at to C, respectively.
From the equation of resistance variation with temperature, we get
This αo is called the temperature coefficient of resistance of that substance at 0oC.

From the above equation, it is clear that the change in electrical resistance of any substance due
to temperature mainly depends upon three factors –
1. the value of resistance at the initial temperature,

2. the rise of temperature and
3. the temperature coefficient of resistance αo.
This αo is different for different materials, so different temperatures are different in different
materials.
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So the temperature coefficient of resistance at 0oC of any substance is the reciprocal of that
substance’s inferred zero resistance temperature.
So far, we have discussed the materials that resistance increases with an increase in temperature.
Still, there are many materials whose electrical resistance of which decreases with a decrease in
temperature.
Actually, in metal, if the temperature increases, the random motion of free electrons and
interatomic vibration inside the metal increase, which result in more collisions.
More collisions resist the smooth flow of electrons through the metal; hence the resistance of the
metal increases with the temperature rise. So, we consider the temperature coefficient of
resistance as positive for metal.
But in semiconductors or other non-metal, the number of free electrons increases with an
increase in temperature.
Because at a higher temperature, due to sufficient heat energy supplied to the crystal, a
significant number of covalent bonds get broken, and hence more free electrons get created.
That means if temperature increases, a significant number of electrons comes to the conduction
bands from valence bands by crossing the forbidden energy gap.
As the number of free electrons increases, the resistance of this type of non-metallic substance
decreases with an increase in temperature. Hence temperature coefficient of resistance is
negative for non-metallic substances and semiconductors.
If there is approximately no change in resistance with temperature, we can consider the value of
this coefficient as zero. The alloy of constantan and manganin has a temperature coefficient of
resistance of nearly zero.
The value of this coefficient is not constant; it depends on the initial temperature on which the
increment of resistance is based.
When the increment is based on an initial temperature of 0oC, the value of this coefficient is αo –
which is nothing but the reciprocal of the respective inferred zero resistance temperature of the
substance.
But at any other temperature, the temperature coefficient of electrical resistance is not the same
as this αo. Actually, for any material, the value of this coefficient is maximum at 0oC
temperature.
Say the value of this coefficient of any material at any toC is αt, then its value can be determined
by the following equation,
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The value of this coefficient at a temperature of t2oC in the term of the same at t1oC is given as,
If at a particular temperature, we know the resistance and temperature coefficient of resistance of

the material, we can find out the resistance of material at other temperatures by using equation
(2).
The Temperature Coefficient of Resistance of some Materials or Substances
Result: We have observed temperature of coefficient resistance.

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Practical No 5
Object: Verify Kirchhoffs' laws..
Theory:
What Is Kirchhoff’s Current Law?
Kirchhoff’s Current Law, often shortened to KCL, states that “The algebraic sum of all currents
entering and exiting a node must equal zero.”
This law is used to describe how a charge enters and leaves a wire junction point or node on a
wire.
Armed with this information, let’s now take a look at an example of the law in practice, why it’s
important, and how it was derived.
Parallel Circuit Review

Let’s take a closer look at that last parallel example circuit:
Solving for all values of voltage and current in this circuit:

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At this point, we know the value of each branch current and of the total current in the circuit. We
know that the total current in a parallel circuit must equal the sum of the branch currents, but
there’s more going on in this circuit than just that. Taking a look at the currents at each wire
junction point (node) in the circuit, we should be able to see something else:
Currents Entering and Exiting a Node

At each node on the positive “rail” (wire 1-2-3-4) we have current splitting off the main flow to
each successive branch resistor. At each node on the negative “rail” (wire 8-7-6-5) we have
current merging together to form the main flow from each successive branch resistor. This fact
should be fairly obvious if you think of the water pipe circuit analogy with every branch node
acting as a “tee” fitting, the water flow splitting or merging with the main piping as it travels
from the output of the water pump toward the return reservoir or sump.
If we were to take a closer look at one particular “tee” node, such as node 6, we see that the
current entering the node is equal in magnitude to the current exiting the node:
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Kirchhoff’s Current Law

Mr. Kirchhoff decided to express it in a slightly different form (though mathematically
equivalent), calling it Kirchhoff’s Current Law (KCL):
Summarized in a phrase, Kirchhoff’s Current Law reads as such:

“The algebraic sum of all currents entering and exiting a node must equal zero”
That is, if we assign a mathematical sign (polarity) to each current, denoting whether they enter
(+) or exit (-) a node, we can add them together to arrive at a total of zero, guaranteed.
Taking our example node (number 6), we can determine the magnitude of the current exiting
from the left by setting up a KCL equation with that current as the unknown value
The negative (-) sign on the value of 5 milliamps tells us that the current is exiting the node, as
opposed to the 2 milliamp and 3 milliamp currents, which must both be positive (and therefore
entering the node). Whether negative or positive denotes current entering or exiting is entirely
arbitrary, so long as they are opposite signs for opposite directions and we stay consistent in our
notation, KCL will work.
Together, Kirchhoff’s Voltage and Current Laws are a formidable pair of tools useful in
analyzing electric circuits. Their usefulness will become all the more apparent in a later chapter
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(“Network Analysis”), but suffice it to say that these Laws deserve to be memorized by the
electronics student every bit as much as Ohm’s Law.
Resistors in Parallel
Let’s look how we could apply Kirchhoff’s current law to resistors in parallel,
whether the resistances in those branches are equal or unequal. Consider the following
circuit diagram:
In this simple parallel resistor example there are two distinct junctions for current.
Junction one occurs at node B, and junction two occurs at node E. Thus we can use
Kirchhoff’s Junction Rule for the electrical currents at both of these two distinct
junctions, for those currents entering the junction and for those currents flowing
leaving the junction.
To start, all the current, IT leaves the 24 volt supply and arrives at point A and from
there it enters node B. Node B is a junction as the current can now split into two
distinct directions, with some of the current flowing downwards and through resistor
R1 with the remainder continuing on through resistor R2 via node C. Note that the
currents flowing into and out of a node point are commonly called branch currents.
We can use Ohm’s Law to determine the individual branch currents through each
resistor as: I = V/R, thus:
For current branch B to E through resistor R1
For current branch C to D through resistor R2

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From above we know that Kirchhoff’s current law states that the sum of the currents
entering a junction must equal the sum of the currents leaving the junction, and in our
simple example above, there is one current, IT going into the junction at node B and
two currents leaving the junction, I1 and I2.
Since we now know from calculation that the currents leaving the junction at node B
is I1 equals 3 amps and I2 equals 2 amps, the sum of the currents entering the junction
at node B must equal 3 + 2 = 5 amps. Thus ΣIN = IT = 5 amperes.
In our example, we have two distinct junctions at node B and node E, thus we can
confirm this value for IT as the two currents recombine again at node E. So, for
Kirchhoff’s junction rule to hold true, the sum of the currents into point F must equal
the sum of the currents flowing out of the junction at node E.
As the two currents entering junction E are 3 amps and 2 amps respectively, the sum
of the currents entering point F is therefore: 3 + 2 = 5 amperes. Thus ΣIN = IT = 5
amperes and therefore Kirchhoff’s current law holds true as this is the same value as
the current leaving point A.
Applying KCL to more complex circuits.

We can use Kirchhoff’s current law to find the currents flowing around more complex
circuits. We hopefully know by now that the algebraic sum of all the currents at a
node (junction point) is equal to zero and with this idea in mind, it is a simple case of
determining the currents entering a node and those leaving the node. Consider the
circuit below.
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Kirchhoff’s Current Law Example No1
In this example there are four distinct junctions for current to either separate or merge
together at nodes A, C, E and node F. The supply current IT separates at node A
flowing through resistors R1 and R2, recombining at node C before separating again
through resistors R3, R4 and R5 and finally recombining once again at node F.
But before we can calculate the individual currents flowing through each resistor
branch, we must first calculate the circuits total current, IT. Ohms law tells us that I =
V/R and as we know the value of V, 132 volts, we need to calculate the circuit
resistances as follows.
Circuit Resistance RAC
Thus the equivalent circuit resistance between nodes A and C is calculated as 1 Ohm.
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Circuit Resistance RCF
Thus the equivalent circuit resistance between nodes C and F is calculated as 10

Ohms. Then the total circuit current, IT is given as:
Giving us an equivalent circuit of:
Kirchhoff’s Current Law Equivalent Circuit
Therefore, V = 132V, RAC = 1Ω, RCF = 10Ω’s and IT = 12A.

Having established the equivalent parallel resistances and supply current, we can now
calculate the individual branch currents and confirm using Kirchhoff’s junction rule as
follows.
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Thus, I1 = 5A, I2 = 7A, I3 = 2A, I4 = 6A, and I5 = 4A.

We can confirm that Kirchoff’s current law holds true around the circuit by using
node C as our reference point to calculate the currents entering and leaving the
junction as:
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We can also double check to see if Kirchhoffs Current Law holds true as the currents
entering the junction are positive, while the ones leaving the junction are negative,
thus the algebraic sum is: I1 + I2 – I3 – I4 – I5 = 0 which equals 5 + 7 – 2 – 6 – 4 = 0.
Kirchhoff’s Voltage Law

Kirchhoff’s Voltage Law (KVL) is Kirchhoff’s second law that deals with the conservation of
energy around a closed circuit path.
Kirchhoff’s Voltage Law Example No1

Three resistor of values: 10 ohms, 20 ohms and 30 ohms, respectively are connected
in series across a 12 volt battery supply. Calculate: a) the total resistance, b) the circuit
current, c) the current through each resistor, d) the voltage drop across each resistor,
e) verify that Kirchhoff’s voltage law, KVL holds true.
a) Total Resistance (RT)

RT = R1 + R2 + R3 = 10Ω + 20Ω + 30Ω = 60Ω
Then the total circuit resistance RT is equal to 60Ω
b) Circuit Current (I)
Thus the total circuit current I is equal to 0.2 amperes or 200mA
c) Current Through Each Resistor

The resistors are wired together in series, they are all part of the same loop and
therefore each experience the same amount of current. Thus:
IR1 = IR2 = IR3 = ISERIES = 0.2 amperes
d) Voltage Drop Across Each Resistor

VR1 = I x R1 = 0.2 x 10 = 2 volts
VR2 = I x R2 = 0.2 x 20 = 4 volts
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VR3 = I x R3 = 0.2 x 30 = 6 volts
e) Verify Kirchhoff’s Voltage Law
Thus Kirchhoff’s voltage law holds true as the individual voltage drops around the closed loop
add up to the total.
Kirchhoff’s Circuit Loop
We have seen here that Kirchhoff’s voltage law, KVL is Kirchhoff’s second law and
states that the algebraic sum of all the voltage drops, as you go around a closed circuit
from some fixed point and return back to the same point, and taking polarity into
account, is always zero. That is ΣV = 0
The theory behind Kirchhoff’s second law is also known as the law of conservation of
voltage, and this is particularly useful for us when dealing with series circuits, as
series circuits also act as voltage dividers and the voltage divider circuit is an
important application of many series circuits.
Result: We Verified Kirchhoff’s Law.

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Practical No 6
Object: Practice of resistor colour coding.
Theory:
Resistors:
A resistor is an electrical component that limits or regulates the flow of electrical current in an
electronic circuit. Resistors can also be used to provide a specific voltage for an active device
such as a transistor.
Standard Resistor Values and Color

Components and wires are coded with colors to identify their value and function.
Resistor Color Coding uses colored bands to quickly identify a resistors resistive value and its
percentage of tolerance with the physical size of the resistor indicating its wattage rating.
Generally, the resistance value, tolerance, and wattage rating are printed on the body of a resistor
as numbers or letters when the resistors body is big enough to read the print, such as large power
resistors.
But when a resistor is smaller (example: 1/4 watt carbon or film type), the print is too small to
read, so the specifications must be shown in another way.
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How to Read Resistor Colour Code?

To read them, hold the resistor such that the tolerance band is on your right. The tolerance band
is usually gold or silver in colour and is placed a little further away from the other bands.
Starting from your left, note down all the colours of the bands and write them down in sequence.
Next, use the table given below to see which digits they represent.
The band just next to the tolerance band is the multiplier band. So if the colour of this band is
Red (representing 2), the value given is 102.
Result: We have Practice Color Code of Resistors.

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Practical No 7
Object: Combine cells in series and parallel and verify the net voltage
Theory:
Cell
We know that electrical current is the flow of charged particles. It is the flow of electrons through a
circuit.
A collection of two or more cells which are connected in series is called A Battery. A battery is an
energy source that converts chemical energy to electrical energy. It is otherwise known
as Electrochemical Cell. The energy is stored in the form of chemical energy inside a battery.
Batteries give us a convenient source of energy for energizing devices without cables and wires.
When it is connected to a circuit it produces electrical energy. A battery consists of two terminals –
A Positive and Negative Terminal. The positive terminal is called Cathode and the negative terminal
is called Anode. They are also called as Electrodes of a Cell. These electrodes will be dipped in a
solution called Electrolyte. It is liquid which is ionic and conducts electricity.
When the battery is about to charge, an external source is connected to it. The anode of the battery is
connected to the negative terminal of the source and cathode is connected to the positive terminal of
the source. As the external source is connected to the battery, electrons are inserted into the anode.
When the cell or battery is connected to the circuit chemical reactions takes place. Thus chemical
reactions takes place within the two electrodes. Here oxidation and reduction reactions hap pens.
Then reduction reaction occurs at cathode and oxidation process occurs at anode.
A dry cell
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The cathode act as the oxidizing agent by accepting electrons from the negative terminal anode. The
anode act as the reducing agent by losing the electrons. Thus due to these chemical reactions an
electrical difference occurs between the terminals-anode and cathode. When there is no power the
electrolyte prohibits the movement of electrons directly from anode to cathode. This is why we are
using an external source or connecting to a circuit. Thus electrons travel from anode to cathode when
the circuit is closed. Finally it gives power to the appliance which is connected to it. After a long
time when the electrochemical process alters the anode and cathode mate rials it stop giving out
electrons. Then the battery dies.
EMF:
EMF or Electromotive force is defined as the potential difference which is developed between the
two terminals of a battery in an open circuit. We know that anode has positive potential (V + ) and
cathode has negative potential (V - ). So emf is the potential difference between the positive terminal
anode and negative terminal cathode when there is no current flowing through it. The emf measures
the energy which is transferred to the charge carries in the cell or a battery. It is the energy in joules
divided by the charge in coulombs. The emf acts as the initiating force for the current to flow.
ε = E/Q, where ε is the electromotive force, E is the energy and Q is the charge.
The emf which is denoted by ε and the equation is given by ε = V + - (-V - ) = V + + V -. It is measured in
volts.
Internal Resistance:
Internal Resistance is the resistance which is present within the battery that resists the current flow
when connected to a circuit. Thus, it causes a voltage drop when current flows through it. It is the
resistance provided by the electrolyte and electrodes which is present in a cell. So Internal resistance
is offered by the electrodes and electrolyte which oppose the current flow inside the cell.
Emf and Internal Resistance Equation:

Consider the circuit given below. The cell can be modified with an emf ε and the internal resistor
with resistance r which is connected in series. An external load resistor with resistance R is also
connected across the circuit. The terminal potential difference represented as V is defined as the
potential difference developed between the positive and negative terminals of the cell when current
flows through the circuit.
V = V + + V - – Ir. This is the voltage drop accomplished due to the internal resistance.
We know that ε = V + + V -. = I (R + r).
ε = IR + Ir.
= V + Ir
V = ε – Ir.
So, V = ε – Ir, where V is the potential difference across the circuit, ε is the emf, I is the current
flowing through the circuit, r is internal resistance.
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Usually internal resistance of a cell is not considered because ε >> Ir. The value of intern al resistance
changes from cell to cell.
Series and Parallel Connections

There are mainly two types of circuits, series and parallel. Cells can be connected both in series,
parallel or a combination of both. In series circuit electrons travel only in one path. Here the current
will be the same which passes through each resistor. The voltage across resistors in a series
connection will be different. Series circuits do not overheat easily. The design of series circuit is
simple compared to parallel circuits.
In parallel circuit electrons travel through many branches in it. In this case, the voltage remains the
same across each resistor in the circuit. Here the current in the circuit is divided among each branch
and finally recombines when the branches meet at a common point. A parallel circuit can be formed
in many ways, which means cells can be arranged in different forms. Parallel circuits can be used as
a current divider. It is easy to connect or disconnect a new cell or other component without affecting
the other elements in the parallel circuit. But it uses a lot of wires and hence becomes complex.
Combination of Cells in Series Connection

Consider two cells which is connected in series. The positive terminal of one cell is connected to
negative terminal of the next cell. Here one terminal of two cells are free and the other terminal of
two cells are joined together. ε 1 and ε 2 are the emfs of the cells and r 1 and r 2 are the internal resistance
of the cells respectively. Let I be the current flowing through the cells.
Cells connected in series

Consider the points A, B and C and let V (A), V (B) and V (C) be the potentials of these points
respectively. V (A) - V (B) will be the potential difference between the positive and negative
terminals for the first cell.
So V AB = V (A) - V (B) = ε 1 - Ir 1.
V BC = V (B) - V (C) = ε 2 – Ir 2.
Now the potential difference between the terminals A and C is
V AC = V (A) – V(C) = [V (A) - V (B)] + V (B) - V (C)]

= ε 1 - Ir 1 + ε 2 – Ir 2
= ( ε 1 + ε 2 ) – I(r 1 +r 2 ).
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In case if we replace this combination of cells by a single cell between the points A and C with emf
ε eq and internal resistance r eq, V AC = ε eq - r eq . and thus we found out that ε eq = ε 1 + ε 2 and r eq = r 1 +r 2 from
the previous equation.
It is clear that the equivalent emf of n number of cells in series combination is the sum of their
individual emfs. The equivalent internal resistance of n cells in series combination is the sum of their
individual internal resistance.
In series combination if the current leaves the cell from the negative electrode, the emf of the cell
will be for example V BC = - ε 2 – Ir 2 and finally the equation for ε eq = ε 1 - ε 2 , (ε 1 > ε 2 ).
Advantages and Disadvantages of cells connected in series:
The cells connected in series produces a greater resultant voltage. The cells which are damaged can
be easily identified and hence can be replaced easily as they break the circuit.
If any one of the cell is damaged in the circuit, it may affect the whole connection. The cells which
are connected in series gets easily exhausted and so they do not last longer. It is not used in house
wiring.
Combination of Cells in Parallel Connection

Consider two cells which is connected in parallel. Here the positive terminals of all cells are
connected together and negative terminals of all cells are connected together. In parallel connection,
the current is divided among the braches. Thus, the current I is split into I 1 and I2. I = I 1 + I2. Consider
the points B 1 and B 2 and then V (B 1 ) and V (B 2 ) are the potentials respectively. The potential
difference across the terminals of the first cell.
Cells connected in parallel

V = V (B 1 ) - V (B 2 ) = ε 1 - I1 r 1. The point B 1 and B 2 are connected similar to the second cell.
V = V (B 1 ) - V (B 2 ) = ε 2 – I 2 r 2 . By ohm’s law we know that I = V / R. Now substitute these values in
the equation
36
If we replace the cells by a single cell lying between the point B 1 and B 2 with emf ε eq and internal
resistance r eq , then V = ε eq - Ir eq .
It is the same as when we connect the resistors in parallel connection.
For n number of cells connected in parallel with emf ε 1, ε 2…… ε n and internal resistance r 1 , r 2…. r n
Advantages and Disadvantages of Cells Connected in Parallel:

For the cells connected in parallel if any one of the cell is damaged in the circuit, it will
not affect the whole connection. The cells which are connected in parallel do not exhaust
easily and thus they last longer.
The voltage developed by the cells in parallel connection cannot be increased by
increasing the number of cells present in the circuit. It is because they do not have same
circular path. In parallel connection the connection provides power based on one cell. So
the brightness of the bulb will not be high.
37
Practical No 8
Object: Study of lead acid battery, practice and use of hydrometer and
electrolyte preparation
Theory:
Lead Acid Battery
Lead Acid battery is commonly used for high power supply. Usually Lead Acid batteries are bigger
in size with hard and heavy
construction, they can store
high amount of energy and
generally used in automobiles
and inverters.
Even after getting competition

with Li-ion batteries, Lead
acid batteries demand is
increasing day by day,
because they are cheaper and
easy-to-handle in comparison
with Li-ion batteries. As per
some market research India
Lead Acid Battery Market is
projected to grow at CAGR of over 9% during 2018-24. So, it has huge market demand in
Automation, Automotive, and Consumer Electronics. Altough most of the Electric vehicle comes
with Lithion-ion batteries, but still there are many electric two wheeler which use Lead Acid
battries to power the vehicle.
In previous tutorial we learned about Lithium-ion batteries, here we will understand the Working,
construction and applications of Lead Acid Batteries. We will also learn about
charging/discharging ratings, requirements and safety of Lead Acid Batteries.
Construction of Lead Acid Battery

What is a Lead Acid Battery? If we break the name Lead Acid battery we will get Lead, Acid,
and Battery. Lead is a chemical element (symbol is Pb and the atomic number is 82). It is a soft
and malleable element. We know what Acid is; it can donate a proton or accept an electron pair
when it is reacting. So, a battery, which consists of Lead and anhydrous plumbic acid (sometimes
wrongly called as lead peroxide), is called as Lead Acid Battery.
38
Electrolyte - as defined in IEEE 1881-2016, IEEE Standard Glossary of Stationary Battery

Terminology is “An aqueous or nonaqueous medium that provides the ion- transport mechanism
between the positive and negative electrodes of a cell.”
Specific Gravity - as defined in IEEE 1881-2016, IEEE Standard Glossary of Stationary Battery
Terminology is “The ratio of the mass of a given volume of electrolyte to the mass of an equal
volume of water at a specified temperature.”
Hydrometer - an instrument, mechanical or electronic, for determining the specific gravity of a
liquid.
An electrolyte sample is drawn into the vessel by squeezing the bulb at the top of the vessel.
Assuming the sample quantity is adequate to result in buoyancy of the float, the level is read
against the float scale to measure specific gravity.
A specific gravity measurement made with a float hydrometer requires temperature and level
correction before it can be considered truly accurate. The reference temperature for lead-acid
batteries in the U.S. is 77°F. One point (.001) of gravity correction is needed for each 3°F above
or below this temperature. Points are added above 77 and subtracted below. Level correction refers
to the location of the electrolyte level in the cell, indicated between the level lines on the side of
the container. Approximately 6 points (.006) are added to the temperature corrected reading for
each ¼” the level is below the high-level line.
Lowering of the level is the result of loss of water in
the electrolyte partly due to evaporation with the
reminder due to electrolysis. The latter of these is
caused by float current passing through the battery
during normal float charging.
Result: we have studied lead acid battery, practice

and use of hydrometer and electrolyte preparation
39
Practical No 9
Object: Practice charging of a lead acid battery
Theory:
Charging Lead Acid Batteries

Battery watering is one part of lead acid battery maintenance. Proper charging practices are just
as critical to optimizing run time and increasing the number of charge cycles in the life of the
battery. Here’s what you need to know:
 Monitor the water levels: Do not let the water level fall below plates.
 Use the correct water type: When topping off your battery’s fill well, always use
distilled or de-ionized water. Tap water typically contains minerals that can damage lead
acid batteries and/or impact performance and lifespan.
 Start the day fully charged: Lead acid batteries should be charged every day after 15
minutes or more of use. Before using the following day, the machine must be plugged in
and charged until the charger indicates the batteries are FULLY charged. Failure to allow
the batteries to fully charge before the next use will diminish the life of the batteries.
 One full charge per day: Do not fully charge lead acid batteries more than once per 24-
hour period to maximize your battery’s life. Opportunity charging, which means plugging
in the machine for a short period of time without fully charging, can negatively impact
the life of the batteries. (Not applicable to TPPL batteries.)
 Fully charge batteries before storing: Lead acid batteries should never be stored in a
discharged state. Some of today’s machines place parasitic loads on the batteries. Even
when the machine’s key is in the “OFF” position, there are electrical components
drawing upon the battery’s energy.
 Check fluid levels: The flooded (wet) lead-acid batteries require routine watering (unless
equipped with Smart- Fill™ Automatic Battery Watering technology). Check the battery
electrolyte level weekly. The electrolyte level should be slightly above the battery plates
as shown before charging. Add distilled water if low. Do not overfill. The electrolyte will
expand and may overflow when charging. After charging, distilled water can be added up
to about 3 mm (0.12 in) below the sight tubes.
 Use the correct charger: The battery charger is set to charge the battery type supplied
with your machine. If you choose to change to a different battery type or capacity, the
charger’s charging profile must be changed to prevent battery damage.
 Seek out new charger technology: Older lead acid battery chargers require careful
monitoring to avoid “over-charging.” But new charger technology allows the batteries
and charger to be plugged in over a weekend or longer. The charger will shut off once the
full charge on batteries is reached. Some newer chargers can monitor the batteries and
turn them back on as the batteries require a charge.
40
 Ideal charging conditions: Charge the batteries in a well-ventilated area of no more than
80 degrees Fahrenheit to prevent possible gas buildup. Never store or charge batteries in
a place that is exposed to freezing temperatures, direct sunlight or heat, or other
temperature extremes.
 Follow your operator manual: All of these battery charging best practices are fairly
universal for all types of lead acid batteries. But, of course, be sure to read the operator
manual for your Tennant cleaning machine for the specific charging protocols.
Result
We have Studied the practice of Charging of Lead Acid Battery.
41
Practical No 10
Object: Study of various types of capacitors and their colour coding
Theory:
Capacitor
A device used to store an electric charge, consisting of one or more pairs of conductors separated
by an insulator.
Capacitor Colour Codes

Capacitor colour codes are a simple and effective visual way of identifying the capacitance value
of a capacitor.
There are two common ways to know the capacitive value of a capacitor, by measuring it using a
digital multimeter, or by reading the capacitor colour codes printed on it. These coloured bands
represent the capacitance value as per the colour code including voltage rating and tolerance.
Sometimes the actual values of capacitance, voltage or tolerance are marked onto the body of a
capacitor in the form of alphanumeric characters. However, when the value of the capacitance is
of a decimal value problems arise with the marking of the “Decimal Point” as it could easily not
be noticed resulting in a misreading of the actual capacitance value.
Instead letters such as p (pico) or n (nano) are used in place of the decimal point to identify its
position and the weight of the number. For example, a capacitor can be labelled as, n47 =
0.47nF, 4n7 = 4.7nF or 47n = 47nF and so on.
Also, sometimes capacitors are marked with the capital letter K to signify a value of one
thousand pico-Farads, so for example, a capacitor with the markings of 100K would be 100 x
1000pF or 100nF.
To reduce the confusion regarding letters, numbers and decimal points, an International colour
coding scheme was developed many years ago as a simple way of identifying capacitor values
and tolerances. It consists of coloured bands (in spectral order) known commonly as a Capacitor
Colour Codes system and whose meanings are illustrated below:
42
43
Capacitor Voltage Reference

Type J – Dipped Tantalum Capacitors.
Type K – Mica Capacitors.
Type L – Polyester/Polystyrene Capacitors.
Type M – Electrolytic 4 Band Capacitors.
Type N – Electrolytic 3 Band Capacitors.
44
The Capacitor Colour Codes system was used for many years on unpolarised polyester and mica
moulded capacitors. This system of colour coding is now obsolete but there are still many “old”
capacitors around. Nowadays, small capacitors such as film or disk types conform to the BS1852
Standard and its new replacement, BS EN 60062, were the colours have been replaced by a letter
or number coded system.
Generally the code consists of 2 or 3 numbers and an optional tolerance letter code to identify the
tolerance. Where a two number code is used the value of the capacitor only is given in
picofarads, for example, 47 = 47 pF and 100 = 100pF etc. A three letter code consists of the two
value digits and a multiplier much like the resistor colour codes in the resistors section.
For example, the digits 471 = 47*10 = 470pF. Three digit codes are often accompanied by an
additional tolerance letter code as given below.
45
Result: We have studied different types of capacitor and their color codes.
46
Practical No 11
Object: Verify laws of combination of capacitors.
Theory
How Capacitors are connected?

Capacitors combination can be made in many ways. The combination is connected to a battery to
apply a potential difference (V) and charge the plates (Q). We can define the equivalent
capacitance of the combination between two points to be
C=QV
Two frequently used methods of combination are: Parallel combination and Series combination
 Capacitor, Types and Capacitance

 Energy Stored in a Capacitor
Parallel Combination of Capacitors

When capacitors are connected in parallel, the potential difference V across each is the same and
the charge on C1, C2 is different i.e., Q1 and Q2.
The total charge is Q given as:

Q=Q1+Q2
Q=C1V+C2V
QV=C1+C2
Equivalent capacitance between a and b is:
47
C = C1 + C2
The charges on capacitors is given as:
 Q1=C1/C1+C2Q
 Q2=C2/C1+C2Q
In case of more than two capacitors, C = C1 + C2 + C3 + C4 + C5 + …………
Series Combination of Capacitors

When capacitors are connected in series, the magnitude of charge Q on each capacitor is same.
The potential difference across C1 and C2 is different i.e., V1 and V2.
Q = C1 V1 = C2 V2
The total potential difference across combination is:
V = V1 + V2
V=Q/C1+Q/C2
VQ=1/C1+1/C2
The ratio Q/V is called as the equivalent capacitance C between point a and b.
The equivalent capacitance C is given by:
1C=1C1+1C2
The potential difference across C1 and C2 is V1 and V2 respectively, given as follows:
V1=C2/C1+C2;V2=C1/C1+C2V
In case of more than two capacitors, the relation is:
1/C=1/C1+1/C2+1/C3+1/C4+……
Important Points:
48
 If N identical capacitors of capacitance C are connected in series, then effective capacitance

= C/N
 If N identical capacitors of capacitance C are connected in parallel, then effective
capacitance = CN
Problem 1: Two capacitors of capacitance C1 = 6 μ F and C2 = 3 μ F are connected in series across

a cell of emf 18 V. Calculate:
 The equivalent capacitance

 The potential difference across each capacitor
 The charge on each capacitor
Sol:
(a)
1/C=1/C1+1/C2
⇒C=C1C2/C1+C2=6×36+3=2μF
(b)
V1=C2/C1+C2V=36+3×18=6volts
V2=C1/C1+C2V=66+3×18=12volts
(c) Q1 = Q2 = C1 V1 = C2 V2 = CV
Charge on each capacitor = Ceq V = 2μF x 18 volts = 36μC
Result:
We have Studied the law of combinations of capacitors.
49
Practical No 12
Object: Observe capacitor charging and discharging.Theory:
Theory:
Capacitors in series and parallel combinations
For practical applications , two or more capacitors are often used in combination and
their total capacitance C must be known.To find total capacitance of the arrangement of
capacitor we would use equation
Q=CV
(i) Parallel combination of capacitors
 Figure below shows two capacitors connected in parallel between two points A and B
 Right hand side plate of capacitors would be at same common potential VA. Similarly left
hand side plates of capacitors would also be at same common potential VB.
 Thus in this case potential difference VAB=VA-VB would be same for both the capacitors,
and charges Q1 and Q2 on both the capacitors are not necessarily equal. So,
Q1=C1V and Q2=C2V
 Thus charge stored is divided amongst both the capacitors in direct proportion to their
capacitance.
 Total charge on both the capacitors is,
Q=Q1+Q2
=V(C1+C2)
and
Q/V=C1+C2 (8)
So system is equivalent to a single capacitor of capacitance
C=Q/V
where,
 When capacitors are connected in parallel their resultant capacitance C is the sum of their
individual capacitances.
 The value of equivalent capacitance of system is greater then the greatest individual one.
 If there are number of capacitors connected in parallel then their equivalent capacitance
would be
C=C1+C2+ C3........... (10)
50
(ii) Series combination of capacitors

 Figure 7 below shows two capacitors connected in series combination between points A
and B.
 Both the points A and B are maintained at constant potential difference VAB.
 In series combination of capacitors right hand plate of first capacitor is connected to left
hand plate of next capacitor and combination may be extended foe any number of
capacitors.
 In series combination of capacitors all the capacitors would have same charge.
 Now potential difference across individual capacitors are given by
VAR=Q/C1
and,
VRB=Q/C2
 Sum of VAR and VRB would be equal to applied potential difference V so,
V=VAB=VAR+VRB
=Q(1/C1 + 1/C2)
or,
where
i.e., resultant capacitance of series combination C=Q/V, is the ratio of charge to total
potential difference across the two capacitors connected in series.
 So, from equation 12 we say that to find resultant capacitance of capacitors connected in
series, we need to add reciprocals of their individual capacitances and C is always less
then the smallest individual capacitance.
 Result in equation 12 can be summarized for any number of capacitors i.e.,
Result: we have Observed capacitor charging and discharging..

51
Practical No 13
Object: Determine of wave length, time period and frequency of a given AC
signal by oscilloscope
Theory:
Oscilloscope:
An oscilloscope is a type of electronic test instrument that graphically displays varying electrical
voltages as a two-dimensional plot of one or more signals as a function of time.
Normally, an oscilloscope is an important tool in an electrical field which is used to display

the graph of an electrical signal as it varies with respect to time. But some of the scopes have
additional features apart from their fundamental use. Many oscilloscopes have the
measurement tool that help us to measure waveform characteristics like frequency, voltage,
amplitude, and many more features with accuracy. Generally, a scope can measure time-
based as well as voltage-based characteristics.
Voltage Measurement
The oscilloscope is mainly voltage oriented device or we can say that it is a voltage
measuring device. Voltage, current and resistance all are internally related to each other.
Parallel In parallel Out shift register Just measure the voltage, rest of the values is obtained
by calculation. Voltage is the amount of electric potential between two points in a circuit. It
is measured from peak-to-peak amplitude which measures the absolute difference between
the maximum point of signal and its minimum point of the signal. The scope displays exactly
the maximum and minimum voltage of the signal received. After measuring all high and low
52
voltage points, scope calculates the average of the minimum and maximum voltage. But you
must be careful to mention which voltage you mean. Normally, oscilloscope has fixed input
range, but this can be easily increased with the use of simple potential divider circuit.
Method to Measure Voltage

The simplest way to measure signal is to set the trigger button to auto that means
oscilloscope start to measure the voltage signal by identifying the zero voltage point or peak
voltage by itself. As any of these two points identified the oscilloscope triggers and measure
the range of the voltage signal.
Vertical and horizontal controls are adjusted so that the displayed image of the sine wave is
clear and stable. Now take measurements along the center vertical line which has the smallest
divisions. Reading of the voltage signal will be given by vertical control.
Current Measurement
Electrical current cannot be measured directly by an oscilloscope. However, it could be
measured indirectly within scope by attaching probes or resistors. Resistor measures the
voltage across the points and then substituting the value of voltage and resistance in Ohm’s
law and calculates the value of electrical current. Another easy way to measure current is to
use a clamp-on current probe with an oscilloscope.
Method to Measure Current

Attach a probe with the resistor to an electrical circuit. Make sure that resistor’s power rating
should be equal or greater than the power output of the system.
Now take the value of resistance and plug into Ohm’s Law to calculate the current.
According to Ohm’s Law,
Frequency Measurement
Frequency can be measured on an oscilloscope by investigating the frequency spectrum of a
signal on the screen and making a small calculation. Frequency is defined as the several
times a cycle of an observed wave takes up in a second. The maximum frequency of a scope
can measure may vary but it always in the 100’s of MHz range. To check the performance of
response of signals in a circuit, scope measures the rise and fall time of the wave.
53
Method to Measure Frequency

Increase the vertical sensitivity to get the clear picture of the wave on the screen without
chopping any of its amplitude off.
Now adjust the sweep rate in such a way that screen displays a more than one but less than
two complete cycles of the wave.
Now count the number of divisions of one complete cycle on the graticule from start to end.
Now take horizontal sweep rate and multiply it with the number of units that you counted for
a cycle. It will give you the period of the wave. The period is the number of seconds each
repeating waveform takes. With the help of period, you can simply calculate the frequency in
cycles per second (Hertz).
Measuring Time and Frequency

The voltage in AC circuits oscillates at a
rate known as the frequency. With an
oscilloscope, you can see and measure
the length of time between signals, and
calculate the frequency of an AC signal.
Adjust the oscilloscope display
Anytime you use an oscilloscope, you

must first adjust the vertical and
horizontal display. Use volts/div and
time/div knobs to adjust the horizontal
scale so one whole cycle fits in the
screen. See Figure 1. After adjusting,
notice the time per division setting on
the display. Figure 1. Adjusting time/div
(Mouse-over to restart animation.)
Measure a time span
Just as you use the volts/div setting to find amplitude, you can use the time/div setting to
calculate a time span. For example, in Figure 1 we see the Channel B signal (red) lags the
Channel A signal (yellow) by 1.2 divisions. With the time/div setting of 50 μs/div, we can
calculate the length of this delay:
54
Measure the wave period

Just as you measured a small time
difference, you can also measure
the period: the time for one complete
wave cycle. Sometimes you can count
the divisions more easily by adjusting
the horizontal position of the wave. In
Figure 2, we see the Channel A signal
repeats after 9.2 divisions. As before,
we can use the time/div setting of
50 μs/div to calculate this length of
time:
Figure 2. Counting time divisions

(Mouse-over to restart animation.)
Calculate the frequency
Knowing the wave period, it is a simple calculation to find the wave frequency. Hint: Use
scientific notation in your calculator.
This should compare well with the approximate frequency indicated by the function generator.
Here are some examples of common metric prefixes you will encounter:
1 μs = 10−6 s 1 ms = 10−3 s 1000 Hz = 1 kHz 106 Hz = 1 MHz
Result:
We have Observed and measured and Determine of wave length, time period and frequency of a
given AC signal by oscilloscope
55
Practical No 14
Object: Draw the forward & reverse characteristics of a P.N. junction diode.
Theory:
Types of Biasing
In a typical diode, forward biasing occurs when the voltage across a diode permits the natural
flow of current, whereas reverse biasing denotes a voltage across the diode in the opposite
direction.
However, the voltage present across a diode during reverse biasing does not produce any
significant flow of current. This unique characteristic is beneficial for changing AC (alternating
current) into direct current (DC).
There are a variety of other uses for this characteristic, including electronic signal control. For
the consideration of this article, we will focus on the PN junction diode and its biasing aspects.
However, there are three biasing conditions and two operating regions for a typical PN junction
diode, and they are as follows:
 Forward bias: Here, the voltage potential connections are as follows: -Ve (negative) to the N-
type material and +Ve (positive) to the P-type material, across the diode. The effect is a
decrease in the PN junction diode's width.
 Reverse bias: During this biasing condition, the voltage potential connections are as follows:
+Ve (positive) to the N-type material and -Ve (negative) to the P-type material, across the
diode. The result of this is an increase in the PN junction diode's width.
 Zero bias: In this biasing state, the PN junction diode does not have an external voltage
potential applied.
56
PN Junction Reverse Bias
As you may know, the bias of a diode (PN junction) in an electrical circuit permits current to
flow more effortlessly in one direction than another. Forward biasing indicates the application of
a voltage across a diode that enables current to flow easily, while reverse biasing means putting a
voltage across a diode in the opposite direction.
In other words, when we apply a voltage across the diode in a manner that the N-type (half) of
the diode connects to the positive terminal of the voltage source, and the P-type (half) connects
to the negative terminal, the electrons from the external circuit will produce more negative ions.
These negative ions are in the P-type region and fill the holes, thus creating more positive ions in
the N-type region. This displaces electrons toward the positive terminal of the voltage source. As
a result, both the voltage between the P-type and N-type regions and the depletion region will
increase. Also, the total charge on either side of the junction will increase in magnitude until the
voltage across the diode equals and opposes the applied voltage. Of course, they cancel each
other out, thus ceasing the flow of current within the circuit.
PN Junction Diode Characteristics
The following are the vital characteristics of a PN junction region (junction diode):
 A semiconductor consists of two types of mobile charge carriers: electrons, and holes.
 Doping can occur in a semiconductor utilizing donor impurities like antimony, and this is
called N-type doping. Also, this doping process contains mobile charges that are mainly
electrons.
 The electrons have a negative charge and the holes have a positive charge.
57
 Doping can also occur in a semiconductor utilizing acceptor impurities such as boron, and this
is called P-type doping. Moreover, this doping process contains mobile charges that are
primarily holes.
 The junction region does not possess charge carriers, and this region is also called the
depletion region.
 The depletion (junction) region's physical thickness will vary with the voltage application.
Forward Biasing versus Reverse Biasing
Here is a list to help further highlight the differences between these two:
 A forward bias diminishes the potential barrier, thus allowing current to flow effortlessly
across the junction. In contrast, a reverse bias reinforces the potential barrier and impedes the
flow of charge carriers.
 With forward biasing, we connect the positive (+) terminal of the voltage supply to the anode
and the negative (-) terminal to the cathode. In contrast, with reverse bias, we connect the
positive (+) terminal of the voltage supply to the cathode and the negative (-) terminal to the
anode.
 A reverse bias strengthens the potential barrier, whereas a forward bias diminishes the
potential barrier of the electric field across the potential.
 A reverse bias has an anode voltage that is less than its cathode voltage. In contrast, a
forward bias has an anode voltage that is greater than the cathode voltage.
 A reverse bias has a marginal forward current, while a forward bias has a significant forward
current.
58
 The depletion layer of a diode is much thicker while in reverse bias and substantially thinner
while in forward bias.
 Reverse bias increases a diode's resistance, and forward bias decreases a diode's resistance.
 A reverse bias does not permit the current to flow, whereas it flows effortlessly in forward
bias through the diode.
 Current is negligible or minimal in reverse bias; however, in forward bias, current levels are
dependent on the forward voltage.
 In reverse bias, a device functions as an insulator and as a conductor while in forward bias.
Result: We have drawn the forward & reverse characteristics of a P.N. junction diode..
59
Practical No 15
Object: Assemble a half wave diode rectifier circuit and observe its input and
out put waveforms
Theory:
What is a Rectifier and Half Wave Rectifier?
A rectifier is a device that converts alternating current (AC) to direct current (DC). It is done by
using a diode or a group of diodes. Half wave rectifiers use one diode, while a full wave rectifier
uses multiple diodes
A half wave rectifier is defined as a type of rectifier that only allows one half-cycle of an AC
voltage waveform to pass, blocking the other half-cycle. Half-wave rectifiers are used to convert
AC voltage to DC voltage, and only require a single diode to construct.
The working of a half wave rectifier takes advantage of the fact that diodes only allow current to
flow in one direction.
A half wave rectifier is the simplest form of rectifier available. We will look at a complete half
wave rectifier circuit later – but let’s first understand exactly what this type of rectifier is doing.
The diagram below illustrates the basic principle of a half-wave rectifier. When a standard AC
waveform is passed through a half-wave rectifier, only half of the AC waveform remains. Half-
wave rectifiers only allow one half-cycle (positive or negative half-cycle) of the AC voltage
through and will block the other half-cycle on the DC side, as seen below.
Since DC systems are designed to have current flowing in a single direction (and constant
voltage – which we’ll describe later), putting an AC waveform with positive and negative cycles
through a DC device can have destructive (and dangerous) consequences. So we use half-wave
rectifiers to convert the AC input power into DC output power.
60
But the diode is only part of it – a complete half-wave rectifier circuit consists of 3 main parts:
1. A transformer
2. A resistive load
3. A diode
A half wave rectifier circuit diagram looks like this:
First, a high AC voltage is applied to the to the primary side of the step-down transformer and
we will get a low voltage at the secondary winding which will be applied to the diode
During the positive half cycle of the AC voltage, the diode will be forward biased and the current
flows through the diode. During the negative half cycle of the AC voltage, the diode will be
reverse biased and the flow of current will be blocked. The final output voltage waveform on the
secondary side (DC) is shown in figure 3 above.
61
This can be confusing on first glance – so let’s dig into the theory of this a bit more.
We’ll focus on the secondary side of the circuit. If we replace the secondary transformer coils
with a source voltage, we can simplify the circuit diagram of the half-wave rectifier as:
Now we don’t have the transformer part of the circuit distracting us.
For the positive half cycle of the AC source voltage, the equivalent circuit effectively becomes:
This is because the diode is forward biased, and is hence allowing current to pass through. So we
have a closed circuit.
But for the negative half cycle of the AC source voltage, the equivalent circuit becomes:
62
This all happens very quickly – since an AC waveform will oscillate between positive and
negative many times each second (depending on the frequency).
Here’s what the half wave rectifier waveform looks like on the input side (Vin), and what it
looks like on the output side (Vout) after rectification (i.e. conversion from AC to DC):
The graph above actually shows a positive half wave rectifier. This is a half-wave rectifier which
only allows the positive half-cycles through the diode, and blocks the negative half-cycle.
The voltage waveform before and after a positive half wave rectifier is shown in figure 4 below.
Result: We have Assembled a half wave diode rectifier circuit and observe its input and out put
waveforms
63
Practical No 16
Object: Assemble a half wave diode rectifier circuit and observe its input
Theory:
Full Wave Rectifier
What is a Full Wave Rectifier?
A full wave rectifier is defined as a type of rectifier that converts both halves of each cycle of an
alternating wave (AC signal) into a pulsating DC signal. Full-wave rectifiers are used to convert
AC voltage to DC voltage, requiring multiple diodes to construct. Full wave rectification is the
process of converting an AC signal to a DC signal.
Circuits that convert alternating current (AC) into direct current (DC) are known as rectifiers. If
such rectifiers rectify both the positive and negative half cycles of an input alternating waveform,
the rectifiers are full-wave rectifiers.
Full-wave rectifiers achieve this by using a group of diodes. A diode permits current in one
direction only and blocks the current in the other direction. We use this principle to construct
various rectifiers.
We can classify rectifiers into two types:
1. Half Wave Rectifier

2. Full Wave Rectifier
When we use a half-wave rectifier, a significant amount of power gets wasted as only one half of
each cycle passes through, and the other cycle gets blocked. Moreover, the half-wave rectifier is
not efficient (40.6%), and we can not use it for applications that need a smooth and steady DC
output. For a more efficient and steady DC output, a full wave rectifier is used
We can further classify full wave rectifiers into:
 Centre-tapped Full Wave Rectifier

 Full Wave Bridge Rectifier
Centre-tapped Full Wave Rectifier
Construction of Centre-tapped Full Wave Rectifier
A centre-tapped full-wave rectifier system consists of:
1. Centre-tapped Transformer
2. Two Diodes
3. Resistive Load
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Centre-tapped Transformer: – It is a normal transformer with one slight modification. It has an

additional wire connected to the exact centre of the secondary winding.
This type of construction divides the AC voltage into two equal and opposite voltages, namely
+Ve voltage (Va) and -Ve voltage (Vb). The total output voltage is
The circuit diagram is as follows.
Working of Centre-tapped Full Wave Rectifier

We apply an AC voltage to the input transformer. During the positive half-cycle of the AC
voltage, terminal 1 will be positive, centre-tap will be at zero potential, and terminal 2 will be
negative potential.
This will lead to forwarding bias in diode D1 and cause current to flow through it. During this
time, diode D2 is in reverse bias and will block current through it.
During the negative half-cycle of the input AC voltage, terminal 2 will become positive relative
to terminal 2 and centre-tap. This will lead to forwarding bias in diode D2 and cause current to
flow through it. During this time, diode D1 is in reverse bias and will block current through it.
During the positive cycle, diode D1 conducts, and during the negative cycle, diode D2 conducts
and during the positive cycle.
As a result, both half-cycles are allowed to pass through. The average output DC voltage here is
almost twice the DC output voltage of a half-wave rectifier.
Output Waveforms
65
Filter Circuit
We get a pulsating DC voltage with many ripples as the output of the centre-tapped full wave
rectifier. We cannot use this pulsating for practical applications.
So, to convert the pulsating DC voltage to pure DC voltage, we use a filter circuit as shown
above. Here we place a capacitor across the load.
The working of the capacitive filter circuit is to short the ripples and block the DC component so
that it flows through another path and is available across the load.
During the positive half-wave, the diode D1 starts conducting. The capacitor is uncharged.
When we apply an input AC voltage that happens to be more than the capacitor voltage, it
charges the capacitor immediately to the maximum value of the input voltage. At this point, the
supply voltage is equal to capacitor voltage.
When the applied AC voltage starts decreasing and less than the capacitor, the capacitor starts
discharging slowly, but this is slower when compared to the charging of the capacitor, and it
does not get enough time to discharge entirely, and the charging starts again.
So around half of the charge present in the capacitor gets discharged. During the negative cycle,
the diode D2 starts conducting, and the above process happens again.
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Full Wave Bridge Rectifier

Construction of Full Wave Bridge Rectifier
A full wave bridge rectifier is a rectifier that will use four diodes or more than that in a bridge
formation. A full wave bridge rectifier system consists of
1. Four Diodes
2. Resistive Load
We use the diodes, namely A, B, C and D, which form a bridge circuit. The circuit diagram is as
follows.
Principle of Full Wave Bridge Rectifier

We apply an AC across the bridge. During the positive half-cycle, terminal 1 becomes positive,
and terminal 2 becomes negative.
This will cause the diodes A and C to become forward-biased, and the current will flow through
it. Meanwhile, diodes B and D will become reverse-biased and block current through them. The
current will flow from 1 to 4 to 3 to 2.
During the negative half-cycle, terminal 1 will become negative, and terminal 2 will become
positive.
This will cause the diodes B and D to become forward-biased and will allow current through
them. At the same time, diodes A and C will be reverse-biased and will block the current through
them. The current will flow from 2 to 4 to 3 to 1.
Filter Circuit
We get a pulsating DC voltage with many ripples as the output of the full wave bridge rectifier.
We can not use this voltage for practical applications.
So, to convert the pulsating DC voltage to pure DC voltage, we use a filter circuit as shown
above. Here we place a capacitor across the load. The working of the capacitive filter circuit is to
short the ripples and block the DC component so that it flows through another path, and that is
through the load.
During the half-wave, the diodes A and C conduct. It charges the capacitor immediately to the
maximum value of the input voltage. When the rectified pulsating voltage starts decreasing and
less than the capacitor voltage, the capacitor starts discharging and supplies current to the load.
This discharging is slower when compared to the charging of the capacitor, and it does not get
enough time to discharge entirely, and the charging starts again in the next pulse of the rectified
voltage waveform.
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So around half of the charge present in the capacitor gets discharged. During the negative cycle,
the diodes B and D start conducting, and the above process happens again. This causes the
current to continue to flow through the same direction across the load.
Full Wave Rectifier Formula

We will now derive the various formulas for a full wave rectifier based on the preceding theory
and graphs above.
Ripple Factor of a Full Wave Rectifier (γ)

‘Ripple’ is the unwanted AC component remaining when converting the AC voltage waveform
into a DC waveform.
Even though we try out best to remove all AC components, there is still some small amount left
on the output side which pulsates the DC waveform. This undesirable AC component is called
‘ripple’.
To quantify how well the half-wave rectifier can convert the AC voltage into DC voltage, we use
what is known as the ripple factor (represented by γ or r).
The ripple factor is the ratio between the RMS value of the AC voltage (on the input side) and
the DC voltage (on the output side) of the rectifier.
The formula for ripple factor is:
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Where Vrms is the RMS value of the AC component, and Vdc is the DC component in the
rectifier.
The ripple factor of a centre-tapped full-wave rectifier is equal to 0.48 (i.e. γ = 0.48).
Note: To construct a good rectifier, we need to keep the ripple factor as minimum as possible.
We can use capacitors or inductors to reduce the ripples in the circuit.
Efficiency of a Full Wave Rectifier (η)

Rectifier efficiency (η) is the ratio between the output DC power and the input AC power. The
formula for the efficiency is equal to:
The efficiency of a centre-tapped full-wave rectifier is equal to 81.2% (i.e. ηmax = 81.2%).
Form Factor of a Full Wave Rectifier (F.F)
The form factor is the ratio between RMS value and average value.
The formula for form factor is given below:
The form factor of a centre-tapped full wave rectifier is equal to 1.11 (i.e. FF = 1.11).
Advantages of Full Wave Rectifiers

The advantages of full wave rectifiers include:
 Full wave rectifiers have higher rectifying efficiency than half-wave rectifiers. This
means that they convert AC to DC more efficiently.
 They have low power loss because no voltage signal is wasted in the rectification
process.
 The output voltage of a centre-tapped full wave rectifier has lower ripples than a
halfwave rectifiers.
Disadvantages of Full Wave Rectifiers

The disadvantages of full wave rectifiers include:
 The centre-tapped rectifier is more expensive than a half-wave rectifier and tends to
occupy a lot of space.
Result: We have Assembled a half wave diode rectifier circuit and observe its input and out put
waveforms

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CIT-134 Electronics I

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CIT-134 Electronics I

Labs Experiments Sign

Lab #1 Study of Ammeter, Voltmeter and Multimeter

Measurement of current, voltage and resistance

Verify the laws of series and parallel combination of

Lab #4 Determine temperature coefficient of resistance

Lab #5 Verify Kirchhoffs' laws

Lab #6 Practice of resistor colour coding

Study of lead acid battery, practice and use of hydrometer and

Lab #9 Study of various types of capacitors and their colour coding.

Lab #10 Verify laws of combination of capacitors

Lab #11 Observe capacitor charging and discharging

Determine of wave length, time period and frequency of a given

Result: We have Studied the Ammeter , Voltmeter and Multimeter.

Verifying OHMS Law by Voltage and Resistance Constant

Experiment to Verify Ohm's Law

Mathematically, this current-voltage relationship is written as,

Equivalent Resistance, Current, and Power in a Series Circuit

This αo is called the temperature coefficient of resistance of that substance at 0oC.

1. the value of resistance at the initial temperature,

If at a particular temperature, we know the resistance and temperature coefficient of resistance of

Result: We have observed temperature of coefficient resistance.

Parallel Circuit Review

Solving for all values of voltage and current in this circuit:

Currents Entering and Exiting a Node

Kirchhoff’s Current Law

Summarized in a phrase, Kirchhoff’s Current Law reads as such:

For current branch C to D through resistor R2

Applying KCL to more complex circuits.

Kirchhoff’s Current Law Example No1

Circuit Resistance RAC

Circuit Resistance RCF

Thus the equivalent circuit resistance between nodes C and F is calculated as 10

Giving us an equivalent circuit of:

Kirchhoff’s Current Law Equivalent Circuit

Therefore, V = 132V, RAC = 1Ω, RCF = 10Ω’s and IT = 12A.

Thus, I1 = 5A, I2 = 7A, I3 = 2A, I4 = 6A, and I5 = 4A.

Kirchhoff’s Voltage Law

Kirchhoff’s Voltage Law Example No1

a) Total Resistance (RT)

b) Circuit Current (I)

Thus the total circuit current I is equal to 0.2 amperes or 200mA

c) Current Through Each Resistor

d) Voltage Drop Across Each Resistor

VR3 = I x R3 = 0.2 x 30 = 6 volts

e) Verify Kirchhoff’s Voltage Law

Kirchhoff’s Circuit Loop

Result: We Verified Kirchhoff’s Law.

Standard Resistor Values and Color

How to Read Resistor Colour Code?

Result: We have Practice Color Code of Resistors.

Emf and Internal Resistance Equation:

Series and Parallel Connections

Combination of Cells in Series Connection

Cells connected in series

V AC = V (A) – V(C) = [V (A) - V (B)] + V (B) - V (C)]

Combination of Cells in Parallel Connection

Cells connected in parallel

It is the same as when we connect the resistors in parallel connection.

Advantages and Disadvantages of Cells Connected in Parallel: