Name: Purely Inductive Circuit
Uploaded: 2019-07-19
Duration: 5 min 40 s
Description: How does an inductor behave in a circuit? This video will explain every parameter involved in the derivation of a pure inductor working with AC supply.

Question

With the help of a labelled diagram, explain the working of a step-up transformer.

Accepted Answer

Labelled diagram of a step-up transformer:

Working:

In a step-up transformer the number of turns in secondary coil $(N_{s})$ are more than the number of turns in primary coil $(N_{p})$ . When an alternating voltage is applied is applied to the primary coil, the resulting current produces an alternating magnetic flux which links the secondary and induces an emf in it. If $ϕ$ is the flux in each turn when the voltage applied to the primary is $v_{p}$ then, the induced voltage in the secondary coil:

$e_{s} = - N_{s} \frac{d ϕ}{d t}$ .....(i)

The alternating flux $ϕ$ also induces a back emf in the primary:

$e_{p} = - N_{p} \frac{d ϕ}{d t}$ .....(ii)

For an ideal transformer:

$e_{s} = v_{s} and e_{p} = v_{p}$ ...(iii)

Using (i), (ii) and(iii):

$\frac{v_{s}}{v_{p}} = \frac{N_{s}}{N_{p}}$

For a hundred percent efficient transformer, the input power is equal to the output power. Hence:

$\frac{i_{p}}{i_{s}} =$ $\frac{v_{s}}{v_{p}} = \frac{N_{s}}{N_{p}}$

Hence, across the secondary coil of a step-up transformer:

$v_{s} = (\frac{N_{s}}{N_{p}}) v_{p}$ and $i_{s} = (\frac{N_{p}}{N_{s}}) i_{p}$

The voltage and current are affected by the transformer as given in the above expressions.

With the help of a labelled diagram, explain the working of a step-up transformer.

Important Questions on Alternating Current

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