2. Kendriya Vidyalaya Kanjikode
Department of Physics
CERTIFICATE
This is to certify that Aravind Ravi, Althaf Younoos and
Jishnu Rajan, students of class XII-B have successfully
completed the research on the below mentioned project
under the guidance of Mr. Sivadas (Subject Teacher)
during the year 2019-20 in partial fulfillment of physics
practical examination conducted by AISSCE, New Delhi.
Signature of external examiner Signature of physics teacher
3. ACKNOWLEDGEMENT
Primarily I would thank God for being able to
complete this project with success. Then I would like to
thank my physics teacher Mr. Sivadas, whose valuable
guidance has been the ones that helped me patch this
project and make it full proof success his suggestions and
his instructions has served as the major contributor
towards the completion of the project.
Then I would like to thank my parents and friends
who have helped me with their valuable suggestions and
guidance has been helpful in various phases of the
completion of the project.
Last but not the least I would like to thank my
classmates who have helped me a lot.
Althaf, Aravind and Jishnu
4. INDEX
1. CERTIFICATE
2. ACKNOWLEDGEMENT
3. AIM OF PROJECT
4. INTRODUCTION
5. THEORY
6. APPARATUS REQUIRED
7. PROCEDURE
8. OBSERVATION
9. RESULT
10. CONCLUSION
11. PRECAUTIONS
12. SOURCES OF ERROR
13. BIBILIOGRAPHY
5. AIM OF THE PROJECT
To investigate the relation between the ratio of :
1. Input and output voltage.
2. Number of turnings in the secondary coil and
primary coil of a self-made transformer.
To find the efficiency of the self-made transformer
6. Introduction
The transformer is a device used for converting a low
alternating voltage to a high alternating voltage or vice-versa.
A Transformer is based on the principle of mutual
induction according to which, a change in magnetic flux linked
with a coil induces an e.m.f in the neighboring coil.
In a transformer, the electrical energy transfer from one
circuit to another circuit takes place without the use of moving
parts.
A transformer which increases the A.C. voltage is called a
Step-up Transformer and one which decreases the A.C.
voltage is called a Step-down transformer.
Transformer is, therefore, an essential piece of apparatus
both for high and low current circuits.
7. Theory
When an alternating voltage is supplied to the primary
coil, it results in a changing magnetic flux, which induces A.C.
Voltage in the secondary coil. In an ideal transformer, whole of
the magnetic flux linked with primary is also linked with the
secondary coil, and then the induced e.m.f. in each turn of the
secondary coil is equal to that induced in each turn of the
primary coil. Thus if Ep and Es are the instantaneous values of
the e.m.f. induced in the primary and the secondary coils, Np
and Ns are the no. of turns of the primary and secondary coils of
the transformer respectively, and dф / dt = rate of change of flux
in each turn of the coil, then we have
Ep = -Np dф / dt _______________ (1)
Es = -Ns dф / dt _______________ (2)
The above relations are true at every instant, so by
dividing (2) by (1), we get
Es / Ep = Ns / Np ______________ (3)
If the transformer is assumed to be 100% efficient (no
energy losses), the input power is equal to the output power,
and since P = IE,
Ip Ep
= Is Es _______________ (4)
8. Therefore, from (3) and (4)
Ns / Np = Es / Ep = Ip / Is = K
Where, N is called Turn Ratio or Transformation Ratio
9. I. Step Up Transformer
In a Step up transformer, low A.C. Voltage is converted to high A.C.
Voltage. Here, the secondary coil has greater no. of turns (Ns > Np), but
carries less current compared to primary (Is < Ip)
Ns / Np > 1, i.e. Turn Ratio (K) is greater than 1
In order to transmit the voltage from the Power Plant or Generation
Station over long distances, it is stepped up using a Step up
Transformer. This voltage with increased levels is then transmitted to
a distribution station.
Illustration
10. II. Step Down Transformer
In a Step down transformer, high A.C. Voltage is converted to low A.C.
Voltage. Here, the secondary coil has lesser no. of turns (Ns < Np), but
carries more current compared to primary (Is > Ip)
Ns / Np < 1, i.e. Turn Ratio (K) is less than 1
At the distribution station, the high voltage from power station is
reduced using a Step down Transformer. The voltage with decreased
level is then made ready for consumer use.
Illustration
11. III. Efficiency
Efficiency of a transformer is defined as the ratio of output
power to the input power. i.e.
η = output power / input power = Es Is / Ep Ip
Thus in an ideal transformer, where there is no power losses, n=1
But in actual practice, there are many power losses; therefore
the efficiency of transformer is less than one.
12. IV. Energy Loses
Following are the major sources of energy loss in a transformer:
1. Copper loss: Energy loss in the form of heat in the copper
coils of a transformer. This is due to joule heating of
conducting wires.
2. Eddy Current: Energy loss in the form of heat in the iron core
of the transformer. This is due to formation of eddy currents
in iron core. It is minimized by taking laminated cores.
3. Leakage of magnetic flux occurs in spite of best insulations.
Therefore, rate of change of magnetic flux linked with each
turn of secondary is less than the rate of change of magnetic
flux linked with each turn of primary.
4. Hysteresis loss: Loss of energy due to repeated
magnetization and demagnetization of the iron core when
A.C. is fed to it.
5. Magneto striation i.e. humming noise of a transformer
13. V. Uses of Transformers
1. In voltage regulator for Television, Refrigerator,
Computer, Air Conditioner etc.
2. A step down transformer is used for welding purposes.
3. A step down transformer is used for obtaining large
current.
4. A step up transformer is used for the production of X-
Rays and NEON advertisement.
5. Small transformers are used in Radio sets, telephones,
loud speakers and electric bells etc.
6. Transformers are used in the transmissions of A.C. over
long distances.
15. Circuit Diagram :
Procedure
1. Take thick iron rod and cover it with a thick paper and
wind a large number of turns of thin Cu wire on thick paper
(say 60). This constitutes primary coil of the transformer.
2. Cover the primary coil with a sheet of paper and
wound relatively smaller number of turns (say 20) of
thick copper wire on it. This constitutes the secondary
coil. It is a step down transformer.
16. 3. Connect primary to A.C main and measure the input
voltage and current using A.C voltmeter and ammeter
respectively.
4. Similarly, measure the output voltage and current
through secondary and record the observations.
5. Now connect secondary to the A.C main, which now
becomes a step up transformer, and again measure
voltage and current through primary and secondary coil.
6. Repeat the above steps by changing the number of
turns in primary and secondary coil.
17. Observation :
Result
The ratio Ns / Np is equal to the ratios Es / Ep and
Ip / Is
Turn Ratio, Ns / Np =
Efficiency =
Sl.
No.
Np NS
Turn
Ratio
K =
Ns/Np
Input Output
Es / Ep Ip / Is
Efficiency
η =
Poutput / Pinput
Es Is / Ep Ip
Voltage
Ep
Current
Ip
Power
P=Ep Ip
Voltage
Es
Current
Is
Power
P=Es Is
18. Conclusion
1. The output voltage of the transformer across
the secondary coil depends upon the ratio of the no.
of turns (Ns / Np)
2. The ratio Ns / Np is equal to the ratios Es / Ep and
Ip / Is
3. There is a loss of power between input and
output coil of a transformer.
19. Precautions
1. All connection must be tight and proper.
2. While taking the readings of current and voltage
the A.C should remain constant.
Sources Of error
1. Values of current can be changed due to heating
effect.
2. Eddy current can change the readings.
