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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.
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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 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. The two coils are wound separately on a laminated soft iron core.
Working: 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. As this changing magnetic flux is linked with both coils, an e.m.f. is induced in each coil. The amount of the magnetic flux linked with the coil depends upon the number of turns of the coil.
Let Φ be the magnetic flux linked per turn with both coils at a certain instant ‘t’. NP and NS be the number of turns of the primary and secondary coils, respectively.
Then at the instant t, the magnetic flux linked with the primary coil ΦP = NPΦ and with the secondary coil ΦS = NSΦ.
The induced emf in the primary and secondary coils will be:
ep = `-(d Phi_p)/(dt) = -N_p(d Phi)/(dt)` ...(1)
es = `-(d Phi_s)/(dt) = -N_s(d Phi)/(dt)` ...(2)
Dividing equation (2) by (1),
∴ `e_s/e_p = N_s/N_p` ...(3)
Equation (3) represents the equation of the transformer.
The ratio `N_s/N_p` is called the turns ratio (transformer ratio) of the transformer.
For an ideal transformer,
Input power = Output power
∴ ePIP = eSIS
∴ `e_s/e_p = I_p/I_s` ....(4)
From equations (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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