Physcis investory project. for your educational purpose....

1. physics Investory project
ON
TRANSFORMER
By,
Nishaanth M s,
XII-CS,
Velammal Vidhyashram

2. 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.
Transformer is, therefore, an essential piece of apparatus both for high
and low current circuits.

3. 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.

4. 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
secondary.
The ideal transformer as a circuit element

5. 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 (1)
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

6. 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
When the resistance of the primary is small, Rp Ip can be neglected so
therefore
E – Ep = 0 or Ep = E
Thus back e.m.f = input e.m.f
Hence equation 3 can be written as Es / Ep = Es / E = output e.m.f / input
e.m.f = Ns / Np = K
Where K is constant, called turn or transformation ratio.
In Step Down Transformer:
Es < E so K < 1, hence Ns < Np
If Ip=value of primary current at
the same instant t
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

7. Ep Ip = Es Is
(or)
Es / Ep = Ip / Is = K
In Step Up Transformer:
Es > E so K > 1, hence Ns > Np
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.

8. 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.

9. 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, 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 part of the energy is lost due to the heat produced in
the resistance of the coil.
4. Hysteresis Loss: The alternating current in the coil tapes the iron
core 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.

10. Resitatial Purpose:
 In voltage regulator for T.V., refrigerator, computer, air
conditioner etc.
 Transformers are used in voltage regulators and stabilized power
supplies.
 Small transformers are used in Radio sets, telephones, loud
speakers and electric bells etc.
 In the induction furnaces.
Industrial Purpose:
 A step down transformer is used for welding purposes.
A step up transformer is used for the production of X-Rays and
NEON advertisement.
For Distribution the current into three phases.
Oil-cooled three-phase distribution transformer, similar to one in
below image, with housing off, showing construction.

11. 1. NCERT 12th
Textbook.
2. Physics lab Manual.
3. www.google.com
4. www.wikipedia.com
5. www.wikibooks.org
6. www.geek.uk

12. Certificate
This is to certify that Nishaanth M S, student of Class XII, Velammal Vidhyashram, has completed
the project titled Transformers during the academic year 2016-2017 towards partial fulfillment of
credit for the Physics practical evaluation of CBSE 2017, and submitted satisfactory report, as
compiled in the following pages, under my supervision.
_________________
Department of Physics
Velammal Vidhyashram School

13. Acknowledgements
"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
Velammal Vidhyashram School for their support during the making of this project.
-NISHAANTH M S

14. The End