This is to certify that Shashi Prakash,
student of Class XII, Sri Guru Nanak
Public School, has completed the project
titled Transformers under the
guidance of Mr. S.K Upadhayay
(physics teacher)during the academic
year 2015-2016 towards partial
fulfillment of credit for the Physics
practical evaluation of CBSE 2016, and
submitted satisfactory report, as compiled
in the following pages, under my
Signature of external examiner
_______________Department of Physics
Sri Guru Nanak Public School
12-01-2016 SHASHI PRAKASH 3
"There are times when silence speaks so much more
loudly than words of praise to only as good as belittle a
person, whose words do not express, but only put a
veneer over true feelings, which are of gratitude at this
point of time."
I would like to express my sincere gratitude to my physics
mentor for his vital support, guidance and encouragement,
without which this project would not have come forth. I would
also like to express my gratitude to the staff of the Department
of Physics at Sri Guru Nanak public School for their support
during the making of this project.
12-01-2016 SHASHI PRAKASH 4
1. CERTIFICATE OF EXCELLENCE
6. THEORY AND WORKING
8. ENERGY LOSSES
9. USES OF TRANSFORMERS
12. SOURCES OF ERROR
12-01-2016 SHASHI PRAKASH 5
The transformer is a device used for converting a low alternating
voltage to a high alternating voltage or a high alternating voltage into
a low alternating voltage. It is a static electrical device that transfers
energy by inductive coupling between its winding circuits. Transformers
range in size from a thumbnail-sized coupling transformer hidden inside
a stage microphone to huge units weighing hundreds of tons used in
power plant substations or to interconnect portions of the power grid.
All operate on the same basic principles, although the range of designs
is wide. While new technologies have eliminated the need for
transformers in some electronic circuits, transformers are still found in
many electronic devices. Transformers are essential for high-voltage
electric power transmission, which makes long-distance transmission
economically practical. A transformer is most widely used device in
both low and high current circuit. 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 voltages
is called a step-up transformer. A transformer which decreases the
A.C. voltages is called a step-down transformer.
12-01-2016 SHASHI PRAKASH 6
Transformer is, therefore, an
essential piece of apparatus
both for high and low current
Close-up of single-phase pole mount
12-01-2016 SHASHI PRAKASH 7
It is based on the principle of mutual
induction that is if a varying current is set-up
in a circuit then induced e.m.f. is produced in
the neighboring circuit. The varying current in
a circuit produce varying magnetic flux which
induces e.m.f. in the neighboring circuit.
12-01-2016 SHASHI PRAKASH 8
A transformer consists of a rectangular shaft
iron core made of laminated sheets, well
insulated from one another. Two coils p1 & p2 and
s1 & s2 are wound on the same core, but are well
insulated with each other. Note that the both the
coils are insulated from the core, the source of
alternating e.m.f is connected to p1p2, the primary
coil and a load resistance R is connected to s1 s2,
the secondary coil through an open switch S. thus
there can be no current through the sec. coil so
long as the switch is open. For an ideal
transformer, we assume that the resistance of the
primary & secondary winding is negligible.
Further, the energy loses due to magnetic the iron
core is also negligible. For operation at low
frequency, we may have a soft iron. The soft iron
core is insulating by joining thin iron strips coated
with varnish to insulate them to reduce energy
losses by eddy currents. The input circuit is called
primary. And the output circuit is called
12-01-2016 SHASHI PRAKASH 9
An ideal voltage step-down
transformer. The secondary current
arises from the action of the secondary
EMF on the (not shown) load
The ideal transformer as a circuit element
12-01-2016 SHASHI PRAKASH 10
THEORY AND WORKING
When an altering e.m.f. is supplied to the
primary coil p1p2, an alternating current
starts falling in it. The altering current in the
primary produces a changing magnetic flux,
which induces altering voltage in the primary
as well as in the secondary. In a good-
transformer, whole of the magnetic flux
linked with primary is also linked with the
secondary, and then the induced e.m.f.
induced in each turn of the secondary is
equal to that induced in each turn of the
primary. Thus if Ep and Es be the
instantaneous values of the e.m.f.’s induced
in the primary and the secondary and Np and
Ns are the no. of turns of the primary
secondary coils of the transformer and, Dфь
/ dt = rate of change of flux in each turn of
the coil at this instant, we have
Ep = -Np Dфь/dt
12-01-2016 SHASHI PRAKASH 11
Es = -Ns Dфь/dt (2)
Since the above relations are true at every
instant, so by dividing 2 by 1, we get
Es / Ep = - Ns / Np (3)
As Ep is the instantaneous value of back e.m.f
induced in the primary coil p1, so the
instantaneous current in primary coil is due to
the difference (E – Ep ) in the instantaneous
values of the applied and back e.m.f. further if
Rp is the resistance o, p1p2 coil, then
the instantaneous current Ip in the primary coil
is given by
I =E – Ep / Rp
E – Ep = Ip Rp
12-01-2016 SHASHI PRAKASH 12
And Is =value of sec. current at this instant,
then Input power at the instant t = Ep Ip and Output
power at the same instant = Es Is
If there are no losses of power in the transformer,
then Input power = output power or
Ep Ip = Es Is Or
Es / Ep = Ip / Is = K
In a step up transformer
As k > 1, so Ip > Is or Is < Ip
I.e. current in sec. is weaker when secondary voltage
is higher. Hence, whatever we gain in voltage, we lose
in current in the same ratio. Similarly it can be shown,
that in a step down transformer, whatever we lose in
voltage, we gain in current in the same ratio.Thus a
step up transformer in reality steps down the current &
a step down transformer steps up the current.
12-01-2016 SHASHI PRAKASH 13
BASIC IDEA OF STEP DOWN TRANSFORMER
BASIC IDEA OF STEP UP TRANSFORMER
12-01-2016 SHASHI PRAKASH 14
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, η = 1. But in actual practice, there
are many power losses; therefore the efficiency
of transformer is less than one.
12-01-2016 SHASHI PRAKASH 15
In practice, the output energy of a transformer is always less than the input energy,
because energy losses occur due to a number of reasons as explained below.
1. Loss of Magnetic Flux: The coupling between the coils is seldom perfect. So,
perfect. So, whole of the magnetic flux produced by the primary coil is not linked up with
the secondary coil.
2. Iron Loss: In actual iron cores in spite of lamination,
Eddy currents are produced. The magnitude of eddy current may, however be small.
And a part of energy is lost as the heat produced in the iron core.
3. Copper Loss: In practice, the coils of the transformer possess resistance. So a
resistance. So a part of the energy is lost due to the heat produced in the resistance of
4. Hysteresis Loss: The alternating current in the coil tapes the iron core through
through complete cycle of magnetization. So Energy is lost due to hysteresis.
5. Magneto restriction: The alternating current in the
Transformer may be set its parts in to vibrations and sound may be produced. It is
called humming. Thus, a part of energy may be lost due to humming.
12-01-2016 SHASHI PRAKASH 16
USES OF TRANSFORMER
A transformer is used in almost all a.c.
In voltage regulator for T.V., refrigerator,
computer, air conditioner etc.
In the induction furnaces.
A step down transformer is used for welding
A step down transformer is used for
obtaining large current.
A step up transformer is used for the
production of X-Rays and NEON
Transformers are used in voltage regulators
and stabilized power supplies.
Transformers are used in the transmissions
of a.c. over long distances.
Small transformers are used in Radio sets,
telephones, loud speakers and electric bells
12-01-2016 SHASHI PRAKASH 17
1. The output voltage of the
transformer across the secondary
coil depends upon the ratio (Ns/Np)
with respect to the input voltage
2. The output voltage of the
transformer across the secondary
coil depends upon the ratio (Ns/N p)
with respect to the input voltage
3. There is a loss of power between
input and output coil of a
12-01-2016 SHASHI PRAKASH 18
1. Keep safe yourself from high
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
12-01-2016 SHASHI PRAKASH 19
A Big Transformer
12-01-2016 SHASHI PRAKASH 20
The data used in this project was
taken from the following sources:
12-01-2016 SHASHI PRAKASH 21
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