1.
KENDRIYA VIDYALAYA SANGATHAN
BENGALURU REGION BENGALURU
“ ”
Submitted in partial fulfillment of the requirements for the AISSCE CBSE Board
examination
In
PHYSICS
For the Academic year
2015-2016
To be carried out by
NAME: NISHANT JHA
REG No:
Under the guidance of
Department of Physics
KENDRIYA VIDYALAYA DRDO C V RAMAN NAGAR
BENGALURU-560093

2.
Certified that the project work entitled Transistors as an Amplifier
and Switch carried out by Kumar Nishant Jha, Roll No , of
class XII ‘C’ is a bonafide work in partial fulfilment of AISSCE in the
subject computer science prescribed by the Central Board of
Secondary Education, during the year 2015-2016. It is certified that all
corrections/suggestions indicated for Internal Assessment have been
incorporated in the Report deposited in the departmental library. The
project report has been approved as it satisfies the academic
requirements in respect of the Project work prescribed for the said
examination.
Name & Signature of the Guide Signature of the Principal

3.
Through this acknowledgement we express our sincere
gratitude to all those people who have been associated with the
project and have helped us with it and made it a worthwhile
experience.
We extend our thanks to Smt. Nutan Punj, the principal of this
fine establishment KV DRDO for being pillar of support
throughout the process.
We would like to express our gratitude towards our parents our
parents for their co-operations and encouragement which
helped us in the completion of this project.
We would also like to express our thanks to Smt. Monika
Chakraborty, the head of physics department of KV DRDO who
gave us this opportunity to learn the subject with a practical
approach, guided us and gave us valuable suggestions regarding
the project.

4.
The invention of the bipolar transistor in 1948 ushered in a
revolution in electronics. Technical feats previously requiring
relatively large, mechanically fragile, power-hungry vacuum
tubes were suddenly achievable with tiny, mechanically rugged,
power-thrifty specks of crystalline silicon. This revolution made
possible the design and manufacture of lightweight, inexpensive
electronic devices that we now take for granted. Understanding
how transistors function is of paramount importance to anyone
interested in understanding modern electronics.
A bipolar transistor consists of a three-layer “sandwich” of
doped (extrinsic) semiconductor materials, either P-N-P in
Figure below (b) or N-P-N at (d). Each layer forming the
transistor has a specific name, and each layer is provided with
a wire contact for connection to a circuit. The schematic
symbols are shown in Figure below (a) and (d).
BJT transistor
(a) PNP schematic symbol (b) layout, (c) NPN symbol (d) layout

5.
The functional difference between a PNP transistor and an
NPN transistor is the proper biasing (polarity) of the junctions
when operating. For any given state of operation, the current
directions and voltage polarities for each kind of transistor are
exactly opposite each other.
Bipolar transistors work as current-controlled
current regulators. In other words, transistors restrict the
amount of current passed according to a smaller, controlling
current. The main current that is controlled goes from collector
to emitter, or from emitter to collector, depending on the type
of transistor it is (PNP or NPN, respectively). The small current
that controls the main current goes from base to emitter, or
from emitter to base, once again depending on the kind of
transistor it is (PNP or NPN, respectively). According to the
standards of semiconductor symbology, the arrow always
points against the direction of electron flow. (Figure below)
Small Base-Emitter current controls large Collector-Emitter
current flowing against emitter arrow.
Bipolar transistors are called bipolar because the main flow of
electrons through them takes place in two types of
semiconductor material: P and N, as the main current goes
from emitter to collector (or vice versa). In other words, two

6.
types of charge carriers—electrons and holes—comprise this
main current through the transistor.
As you can see, the controlling current and
the controlled current always mesh together through the
emitter wire, and their electrons always flow against the
direction of the transistor’s arrow. This is the first and foremost
rule in the use of transistors: all currents must be going in the
proper directions for the device to work as a current regulator.
The small, controlling current is usually referred to simply as
the base current because it is the only current that goes
through the base wire of the transistor. Conversely, the large,
controlled current is referred to as the collector
current because it is the only current that goes through the
collector wire. The emitter current is the sum of the base and
collector currents, in compliance with Kirchhoff’s Current Law.
No current through the base of the transistor, shuts it off like an
open switch and prevents current through the collector. A base
current, turns the transistor on like a closed switch and allows
a proportional amount of current through the collector.
Collector current is primarily limited by the base current,
regardless of the amount of voltage available to push it. The
next section will explore in more detail the use of bipolar
transistors as switching elements.

7.
i. Breadboard – 1
ii. Transistor: BC547 (NPN) – 1
iii. Preset: 10 kΩ – 1
iv. LED – 2
v. Resistor: 330 Ω ‐ 2
Colour Code: 330 Ω – Orange Orange Brown Gold
vi. 9V Battery – 1
vii. Connecting Wire Pieces
viii. Multimeter – 1

8.
PHOTO OF THE CIRCUIT
MADE BY THE MEMBERS OF
THE TEAM

9.
THEORY
In common emitter circuit of a transistor, emitter base make
input section and is forward biased and emitter collector
junction make output section and is reverse biased.
The variation in the output voltage w.r.t. the variation in input
voltage for a transistor are shown in figure.
The amount of amplification is decided by the β (beta) of the
transistor.
𝛽 = ℎ𝑓𝑒 = 𝐼 𝐶/𝐼 𝐵
Where,
 IC is the collector current.
 IB is the base current.
β is an intrinsic property of the transistor. Different transistors
have different betas.

10.
For this, experiment we will use the transistors in the
common-emitter configuration. The input signal is applied
between the base and emitter, and the output is taken from
the collector and emitter.
Circuit diagram: transistor as amplifier and switch

11.
1. In this circuit two same-colored LEDs are used so that the
effect of amplification can be clearly seen.
2. The emitter of the transistor is grounded.
3. A preset (10 kΩ) is used in the circuit. It is used as a
voltage divider to apply different voltages at the base. To
use preset as a voltage divider, either of the side
terminals is given Vcc and the other ground.
4. The middle terminal of the preset is connected in series
with the positive terminal of LED1. The negative terminal
of LED1 is connected in series with a resistor R1 (330 Ω).
The other end of the resistor is connected to the base of
the transistor.
5. One end of resistor, R2 (330 Ω) is connected to the
collector. The other end of the corresponding resistor is
connected to the negative terminal of LED2.
6. The positive terminal of LED2 is connected to Vcc.

12.
PROCEDURE
1. Make the circuit diagram (on breadboard, if possible).
2. Make all connections neat, clean and tight.
3. Now, set a particular input voltage (VI) using the preset,
and measure it. Also, measure the voltages at the base
(VB) and collector (VC) and compare them.
4. Measure the base current (IB) and the collector current
(IC) and verify the amplification factor.
5. Now, rotate the preset to a position, where both the LEDs
glow brightly. At this position, measure the input voltage
(VI) at the middle terminal of the preset. Also, measure
the voltages at the base (VB) and collector (VC) and
compare them.
6. Again, measure the base current (VB) and the collector
(VC) current and verify the amplification factor.

13.
1. For the first reading :-
 VI = 3.02 V
 VB = 0.63 V
 VC = 6.36 V
 IB = 9 μA
 IC = 3.22 mA = 3220 μA
2. For the second reading :-
 VI = 8.29 V
 VB = 0.89 V
 VC = 0.03 V
 IB = 12.27 mA
 IC = 15.98 mA

14.
1. For the first reading :-
 Current Gain, β = hfe = IC / IB = 3220 / 9 ≅ 358
 Voltage Gain, A = VO / VI = 6.36 / 3.02 ≅ 2.1
 Power Gain, P = β * A = 358 * 2 = 716
2. For the second reading :-
 Current Gain, β = hfe = IC / IB = 15.98 / 12.27 = 1.3
 Voltage Gain, A = VO / VI = 0.03 / 8.29 ≅ 3.6 X 10-3
 Power Gain, P = β * A = 1.3 * 3.6 X 10-3
= 359

15.
 For the first readings, VB is less than the collector
voltage VC. Since the base voltage is less than the
collector voltage, we can say that the base ‐ collector
junction is reverse biased. This is a necessary condition
for the transistor to be in the active region. The value
of β (hFE) for this transistor should be between
100 ‐ 400. The calculated value, 358, lies in this range.
This means that the transistor is in the active region.
 So, in the active region, the transistor acts as an
amplifier as long as the base ‐ emitter junction is
forward biased and the base ‐ collector junction is
reverse biased.
 Now, for the second reading, on comparing the base
and the collector voltages, we can see that the base
voltage VB is more than the collector voltage VC. Since
the base voltage is more than the collector voltage, we
can say that the base ‐ collector junction is forward
biased. This is a necessary condition for the transistor
to be in the saturation region.
Also, the collector voltage is close to zero volt
(ground).
 The value of β (hFE), 1.3, is less than the ideal gain
(100) of a transistor. This means, the transistor does
not act as an amplifier in this case, it acts like a

16.
switch. In the saturation region, the collector - emitter
voltage VCE is reduced to almost 0 V. We can see that
the value of the collector voltage with respect to the
emitter (ground) is 0.03 V. The collector and emitter
act as two terminals of the switch, which get nearly
shorted.
 In the active region, the transistor acts as an amplifier
as long as the base ‐ emitter junction is forward biased
and the base ‐ collector junction is reverse biased.
 A transistor gets saturated when its base ‐ emitter
junction and base ‐ collector junction are forward
biased. In saturation, the potential difference
between the emitter and the collector is
approximately equal to zero volt. This voltage across
the collector ‐ emitter junction is called the
collector ‐ emitter saturation voltage. The value of
the saturation region for the NPN transistor in my
project is around 0.25 ‐ 0.6 V.

17.
1. All connections should be neat, clean and tight.
2. The input voltage should be increases gradually.
3. Don’t connect the terminals of the battery to each
other.
 The transistor may be faulty.
 Guidance from Teacher
 NCERT Class 12 Physics Book
 Comprehensive Physics Practical Book
 www.cooljunk.in/physics-project-kit
 www.google.com