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Questions
Describe the construction and working of a transformer with a neat labelled diagram.
Explain the working of a transformer with a neat, labelled diagram.
Solution
Principle:
It is based on the principle of mutual induction, i.e., whenever the magnetic flux linked with a coil changes, an e.m.f is induced in the neighbouring coil.
- Construction:
a. A transformer consists of two sets of coils, primary P and secondary S, insulated from each other. Coil P is called the input coil, and coil S is called the output coil.
b. The two coils are wound separately on a laminated soft iron core.
- Working:
a. When an alternating voltage is applied to the primary coil, the current through the coil goes on changing. Hence, the magnetic flux through the core also changes.
b. As this changing magnetic flux is linked with both the coils, an e.m.f is induced in each coil.
c. The amount of the magnetic flux linked with the coil depends upon the number of turns of the coil.
d. Let, ‘Φ’ be the magnetic flux linked per turn with both the coils at a certain instant ‘t’.
e. Let ‘NP' and ‘NS’ be the number of turns of the primary and secondary coil,
NPΦ = magnetic flux linked with the primary coil at a certain instant ‘t’
NSΦ = magnetic flux linked with the secondary coil at a certain instant ‘t’
f. Induced e.m.f produced in the primary and secondary coil is given by,
`"e"_"p" = -("d"phi_"p")/"dt" = -"N"_"p"("d"phi)/"dt"` ….(1)
`"e"_"s" = -("d"phi_"s")/"dt" = -"N"_"s"("d"phi)/"dt"` ….(2)
g. Dividing equation (2) by (1),
∴ `"e"_"s"/"e"_"p" = "N"_"s"/"N"_"p"` ….(3)
Equation (3) represents equation of transformer.
The ratio `"N"_"s"/"N"_"p"` is called turns ratio (transformer ratio) of the transformer.
h. For an ideal transformer,
Input power = Output power
∴ ePIP = eSIS
∴ `"e"_"s"/"e"_"p" = "I"_"p"/"I"_"s"` ….(4)
i. From equation (3) and (4),
`"e"_"s"/"e"_"p" = "N"_"s"/"N"_"p" = "I"_"p"/"I"_"s"`
Notes
Students should refer to the answer according to their questions.
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