ACKNOWLEDGEMENT

I would like to sincerely thank all those who contributed to the successful
completion of my Physics investigatory project.
First, I am deeply grateful to Mr. Suresh Kumar S.K., my Physics teacher,
for his guidance and support throughout this project. His knowledge, clear
direction, and continuous encouragement helped me overcome challenges
and refine my approach. His constructive feedback was instrumental in
improving my work and achieving the desired outcome.
I also extend my heartfelt thanks to my father, whose insights and
understanding of the topic greatly helped me with the theoretical aspects.
His guidance allowed me to approach the experiment with confidence and
clarity. Additionally, I am thankful to my mother for her emotional support
and motivation, which helped me stay focused and dedicated to my work
during difficult times. Her belief in my abilities was a great source of
strength.
Lastly, I would like to express my gratitude to my friends for their valuable
suggestions and collaboration. They played a key role in shaping the idea
and motivating me throughout the project. Their encouragement and
feedback kept me motivated, and I am grateful for their support. I also
appreciate everyone who helped me in any way, as their contributions made
this project a success.
 TABLE OF CONTENTS

Sl. Page
Title
No. No.
1 Introduction 1

2 Objective 3

3 Materials Required 4

4 Theory 5

5 Circuit Diagram 7

6 Procedure 8

7 Observations 10

8 Results 12

9 Precautions 13

10 Sources Of Error 14

9 Conclusion 15

10 Applications 16

11 Bibliography 18
 INTRODUCTION
A transformer is a static electrical device used to transfer electrical
energy between two or more circuits through electromagnetic
induction. It is essential for either increasing (step-up) or decreasing
(step-down) voltage levels in power distribution systems. The
transformer operates based on Faraday’s Law of Electromagnetic
Induction, which states that a change in magnetic flux through a coil
induces an electromotive force (EMF) across the coil. This principle is
fundamental to the working of all transformers.

Working Principle of a Transformer

The transformer consists of two coils: the primary coil (connected to
the input voltage source) and the secondary coil (providing the output
voltage). When alternating current (AC) flows through the primary
coil, it generates a fluctuating magnetic field. This magnetic field
induces a voltage in the secondary coil due to electromagnetic
induction. The ratio of voltages between the primary and secondary
coils is directly related to the ratio of the number of turns of wire in
each coil, which is a direct consequence of Faraday’s Law.
Transformer Equation
The relationship between the voltages and the number of coils (turns)
is given by
Voltage Ratio (derived from Faraday’s Law of Induction):

𝑉𝑝 𝑁𝑝
=
𝑉𝑠 𝑁𝑠

1
Objective of the Project
The goal of this investigatory project is to examine the relationship
between the input and output voltages of a self-designed transformer
by varying the number of coils in the primary and secondary coils.
Specifically, the project seeks to determine how the number of turns
influences the voltage transformation ratio.

Key aspects of the project include:

• Understanding the role of the number of turns in determining the
voltage ratio.
• Investigating how changing the number of coils impacts the
input-output voltage relationship.
• Exploring the overall efficiency of the transformer with varying
coil turns.
•

This project will help deepen the understanding of transformer design

and performance, with potential applications in electrical power
distribution and various engineering fields.

2
 OBJECTIVE

OBJECTIVE OF THE PROJECT -

To investigate the relationship between the ratio of

i. input and output voltage, and
ii. Number of turns in the secondary coil and primary coil of a self
designed transformer
by varying the number of turns in the primary and secondary coils,
and to verify the transformer equation:

𝑉𝑝 𝑁𝑝
=
𝑉𝑠 𝑁𝑠

3
 MATERIALS REQUIRED

1. Enamelled copper wire – for winding the primary and secondary

coils
2. Soft iron core (U/I or E/I laminated core) – to concentrate the
magnetic field
3. AC power supply (6V–12V) – to provide input voltage to the primary
coil
4. Voltmeter – to measure input and output voltages
5. Ammeter (optional) – to measure current if required
6. Wooden/plastic baseboard – to mount the transformer securely
7. Insulating tape or zip ties – to secure the windings in place
8. Connecting wires and crocodile clips – for safe electrical
connections
9. Screwdriver and wire stripper – for assembling and connecting
components

4
 THEORY
The working of a transformer is based on the phenomenon of mutual
induction. In an ideal transformer, the primary and secondary coils have
negligible resistance, and all the magnetic flux links both the primary and
secondary windings.
When alternating current (AC) flows through the primary coil, it generates
a time-varying magnetic field. This magnetic field is concentrated through
a soft iron core, which links the secondary coil and induces an
electromotive force (EMF) in it.
As per Faraday’s Second Law of Electromagnetic Induction, the EMF
induced is proportional to the rate of change of magnetic flux:

• In the primary coil:

𝑑𝛷
𝐸𝑝 = −𝑁𝑝
𝑑𝑡

• In the secondary coil:

𝑑𝛷
𝐸𝑠 = −𝑁𝑠
𝑑𝑡

Where,
Np = Number of turns in the primary coil
Ns = Number of turns in the secondary coil
𝛷 = Magnetic flux linked with each turn of both coils
𝑑𝛷
= Rate of change of magnetic flux
𝑑𝑡

5
Ideal Transformer Assumptions
An ideal transformer is one where all the magnetic flux produced by the
primary coil links with the secondary coil, there are no energy losses, and
the core is perfectly magnetically coupled.
Derivation of the Transformer Equation
Since the induced EMF in the primary and secondary coils is proportional
to the number of turns in each coil, we can take the ratio of the EMFs:

𝑑𝛷
𝐸𝑝 −𝑁𝑝 𝑑𝑡
=
𝐸𝑠 −𝑁𝑠 𝑑𝛷
𝑑𝑡
i.e.
𝐸𝑝 𝑁𝑝
=
𝐸𝑠 𝑁𝑠
EMF to Voltage
Under sinusoidal steady-state, the RMS voltage across each coil equals the
RMS value of the induced EMF (neglecting any drops in winding
resistance):

𝑉𝑝 𝑁𝑝
=
𝑉𝑠 𝑁𝑠

Step-Up and Step-Down Transformers

Based on the ratio of coil turns, transformers are classified as:
• Step-Up Transformer: 𝑁𝑠 > 𝑁𝑝 and 𝑉𝑠 > 𝑉𝑝, increases voltage
• Step-Down Transformer: 𝑁𝑠 < 𝑁p and 𝑉𝑠 < 𝑉𝑝 , decreases voltage

This experiment uses a self-made transformer to verify the voltage-turns

relationship by varying secondary coil turns while keeping input voltage and
primary turns constant.

6
CIRCUIT DIAGRAM

7
 PROCEDURE
STEP-UP TRANSFORMER

1. Take a thick iron rod, cover it with insulating paper, and wind a large
number of thin copper wire turns for the primary coil.
2. Cover the primary coil with insulating paper and wind a smaller
number of thicker copper wire turns around it to form the secondary
coil.
3. Connect the primary coil’s terminals (P1P2) to the AC mains supply,
ensuring proper insulation and safety from electrical hazards during
operation.
4. Measure the input voltage across the primary coil using an AC
voltmeter and the current using an ammeter connected to the primary
coil.
5. Measure the output voltage and current across the secondary coil
using an AC voltmeter and ammeter for comparison with the input
measurements.
6. Increase the number of turns in the secondary coil while keeping the
number of turns in the primary coil constant. This will reduce the
output voltage.
7. Record the new output voltage and current after adjusting the number
of turns in the secondary coil for each configuration.
8. Repeat the process by varying the number of turns in the secondary
coil while keeping the primary coil’s turns constant, and observe the
corresponding changes in output voltage.

8
STEP-DOWN TRANSFORMER

1. Take a thick iron rod, cover it with insulating paper, and wind a large
number of thin copper wire turns for the primary coil.
2. Cover the primary coil with insulating paper and wind a smaller
number of thicker copper wire turns around it to form the secondary
coil.
3. Connect the primary coil’s terminals (P1P2) to the AC mains supply,
ensuring proper insulation and safety from electrical hazards during
operation.
4. Measure the input voltage across the primary coil using an AC
voltmeter and the current using an ammeter connected to the primary
coil.
5. Measure the output voltage and current across the secondary coil
using an AC voltmeter and ammeter for comparison with the input
measurements.
6. Reduce the number of turns in the secondary coil while keeping the
number of turns in the primary coil constant. This will reduce the
output voltage.
7. Record the new output voltage and current after adjusting the number
of turns in the secondary coil for each configuration.
8. Repeat the process by varying the number of turns in the secondary
coil while keeping the primary coil’s turns constant, and observe the
corresponding changes in output voltage.

9
 OBSERVATION
1. Least count of voltmeters =
2. Zero error of voltmeters =
3. Range of voltmeters =
4. Least count of ammeters =
5. Zero error of ammeters =
6. Range of ammeters =
7. Applied A.C. voltage =

FOR STEP-UP TRANSFORMER

Number of Number of
Input Input Output Output
Sl. turns in turns in
Voltage Current Voltage Current
No. primary secondary
(Vp) (Ip) (Vs) (Is)
coil (Np) coil (Ns)

10
FOR STEP-DOWN TRANSFORMERS

Number of Number of
Input Input Output Output
Sl. turns in turns in
Voltage Current Voltage Current
No. primary secondary
(Vp) (Ip) (Vs) (Is)
coil (Np) coil (Ns)

11
 RESULTS
• The experiment confirmed that the output voltage of the transformer
is directly proportional to the number of turns in the secondary coil.
By varying the turns in the secondary while keeping the primary turns
and input voltage constant, a clear and consistent relationship was
𝑉𝑝 𝑁𝑝
observed, validating the transformer equation =
𝑉𝑠 𝑁𝑠

• In the step-up configuration (where secondary turns > primary turns),

the output voltage increased as expected. Conversely, in the step-
down setup (where secondary turns < primary turns), the output
voltage decreased accordingly. This demonstrated the practical effect
of the turns ratio on voltage transformation.

• While the transformer equation held true for voltage ratios, minor
discrepancies in output power indicated the presence of power loss.
These could be due to factors like winding resistance, core heating, or
small leakage of magnetic flux, showing that the transformer was not
perfectly ideal.

12
 PRECAUTIONS
1. All electrical connections must be tight, secure, and properly insulated
to prevent power loss or short circuits.

2. Only alternating current (AC) should be used, as transformers do not

function with direct current (DC).

3. The soft iron core must be properly aligned to ensure efficient

magnetic flux linkage between the primary and secondary coils.

4. The input voltage should be kept within safe limits to avoid

overheating or damaging the coils.

5. Avoid disturbing the setup during measurements to ensure consistent

and accurate readings.

6. Only accurate and calibrated measuring instruments (voltmeters and

ammeters) should be used for better precision.

7. The power supply must be switched off before modifying coil

connections or changing the number of turns.

13
 SOURCES OF ERROR

1. Power loss due to internal resistance in the copper wires of both

primary and secondary coils.

2. Incomplete magnetic flux linkage caused by air gaps or poor

alignment of the iron core.

3. Errors in counting the number of turns during manual winding of

coils.

4. Parallax error while taking readings from analog voltmeters or

ammeters.

5. Heating of the coils during operation, which can change wire

resistance and affect results.

6. Voltage fluctuations in the AC power supply can lead to inconsistent

measurements.

7. Eddy currents generated in the iron core may lead to energy loss,
causing inefficiency in the transformer.

14
 CONCLUSION
The experiment aimed to investigate the relationship between the input and
output voltages of a transformer by varying the number of turns in the
secondary coil while keeping the primary coil turns and input voltage
constant. A self-constructed transformer was used to demonstrate how
voltage transformation occurs based on the principle of mutual induction.
The results obtained from the observation table clearly showed that the
output voltage is directly proportional to the ratio of the number of turns in
the secondary coil to that in the primary coil. This verified the transformer
equation:

𝑉𝑝 𝑁𝑝
=
𝑉𝑠 𝑁𝑠

which relates the secondary and primary voltages to their respective number
of turns.
When the number of turns in the secondary coil was greater than that in the
primary, the transformer acted as a step-up transformer, resulting in a higher
output voltage. Conversely, when the number of turns in the secondary coil
was fewer than in the primary, the output voltage dropped, indicating step-
down transformer behavior.
These experimental findings are in agreement with Faraday’s Law of
Electromagnetic Induction and the ideal transformer model, where energy
losses are assumed to be negligible. The experiment successfully
demonstrated how varying the number of turns influences voltage
transformation, thereby validating the theoretical principles.

15
 APPLICATIONS
Transformers operate on the principle that the voltage induced in each coil
is proportional to the number of turns in that coil. The turns ratio (Ns/Np)
determines whether the transformer increases (step-up) or decreases (step-
down) the voltage. When the secondary coil has more turns than the primary,
the voltage is stepped up, and when the secondary has fewer turns, the
voltage is stepped down. This ratio is crucial for adjusting voltage levels to
meet specific real-life application needs.

Step-Up Transformer Applications:

In step-up transformers, the secondary coil has more turns, increasing output
voltage.

1. Electric Power Transmission: Step-up transformers increase voltage

to reduce current, minimizing energy loss during long-distance
transmission over power lines.

2. X-ray Machines: Step-up transformers provide the necessary high

voltage for generating X-rays, ensuring efficient image production in
medical diagnostics.

3. Microwave Ovens: Step-up transformers raise voltage to power the

magnetron, generating microwaves for efficient cooking or heating of
food.

4. Renewable Energy Systems: Step-up transformers boost voltage

from solar and wind systems, ensuring efficient transmission of
energy to the power grid.

5. Electric Locomotives: Step-up transformers increase voltage to

power high-speed trains, enabling efficient operation and reducing
energy losses.

16
Step-Down Transformer Applications:
In step-down transformers, the secondary coil has fewer turns, lowering
output voltage.

1. Domestic Power Supply: Step-down transformers lower high

transmission voltage to safe levels for household appliances, ensuring
safe electrical usage.

2. Phone and Laptop Chargers: Step-down transformers convert high

mains voltage to lower, safe voltage for charging electronic devices
like phones and laptops.

3. Electric Welding Machines: Step-down transformers provide low

voltage and high current, enabling safe and efficient welding
operations in industries.

4. Power Adapters for Small Devices: Step-down transformers reduce

voltage to appropriate levels for powering small electronic devices
such as toys or gadgets.

5. Power Distribution Substations: Step-down transformers reduce

voltage from high transmission lines to lower levels suitable for local
distribution to homes and businesses.

17
 BIBLIOGRAPHY
1. NCERT Class XII Physics Textbook (Part 2)
Published by NCERT, New Delhi

2. Comprehensive Practical Physics – Class XII

Published by Laxmi Publications

3. Reference Websites:
o https://en.wikipedia.org/wiki/Transformer
o https://www.cbse.gov.in
o https://www.youtube.com

18