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ACKNOWLEDGEMENT
I would like to express my special thanks
of gratitude to my Physics teacher,
Mr.Sujanapal as well as our Principal
Mr.S.S.U.Tabrez who gave me this
opportunity to do this project on the
topic ‘Black Hole Thermodynamics’. It
helped me in doing a lot of research and
through it I came to know about so
many new things. I am really thankful to
them.
Secondly I would like to thank my
parents and friends who helped me a lot
in finishing this project within the limited
time.
I would also like to thank the CBSE
board for giving me this opportunity to
explore beyond the regular NCERT
textbook.
INDEX
1. Introduction..........................
......page 3
2. Objective..............................
.........page 5
3. Theory...................................
........page 6
4. Apparatus.............................
.....page 11
5. Circuit
Diagram.......................page 13
6. Procedure..............................
....page 14
As such transformers are built in an
amazing strength of sizes. In electronic,
measurement and control circuits,
transformer size may be so small that it
weight only a few tens of grams where
as in high voltage power circuits, it may
weight hundreds of tones.
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.
OBJECTIVE
To investigate the relation between
the ratio of:
- Input and output voltage.
- Number of turnings in the secondary coil and primary coil of a self-made transformer.
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: dф / dt = rate of change of flux in each turnoff the coil at this instant, we have Ep = -Np dф/dt _______________ (1) And Es = -Ns dф/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: Ip = 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
Es > E so K > 1, hence Ns > Np As, k > 1, so Ip > Is or Is < Ip i.e. current in secondary 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.
IN A STEP-DOWN TRANSFORMER:
Es < E so K < 1, hence Ns < Np
If Ip = value of primary current at the same instant And Is = value of secondary current at this instant, then Input power at the instant = 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
Voltmeter: Ammeter:
CIRCUIT DIAGRAM
60). This constitutes primary coil of the transformer. 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. Connect p1, p2 to A.C main and measure the input voltage and current using A.C voltmeter and ammeter respectively. Similarly, measure the output voltage and current through s1and s2. Now connect s1and s2to A.C main and again measure voltage and current through primary and secondary coil of step up transformer. Repeat all steps for other self-made transformers by changing number of turns in primary and secondary coil.
USES OF TRANSFORMER
A transformer is used in almost all a.c.
operations:
In voltage regulator for T.V., refrigerator, computer, air conditioner, etc. A step down transformer is used for welding purposes. A step down transformer is used for obtaining large current. A step up transformer is used for the production of X-Rays and NEON advertisement. 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 etc.
SOURCES OF ERROR
Keep safe yourself from high voltage. While taking the readings of current and voltage the A.C should remain constant.
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