Question

Explain with the help of a labelled diagram the

underlying principle and working of a step-up

transformer. Why cannot such a device be used

to step-up dc voltage ?

Answer 1

Transformer:

Principle: It is a device which converts high voltage AC into low voltage AC and vice-versa. It is based upon the principle of mutual induction. When alternating current is passed through a coil, an induced emf is set up in the neighbouring coil.

Working: When an alternating current is passed through the primary, the magnetic flux through the iron core changes, which does two things. It produces emf in the primary and an induced emf is also set up in the secondary. If we assume that the resistance of primary is negligible, then the back emf will be equal to the voltage applied to the primary.

V1 = -N1 dΦ/dt and

V2 = -N2 dΦdt

Where, N1 and N2 are number of turns in the primary and the secondary respectively and V1 and V2 are their voltages respectively.

V2/V1 = N1/N2

In a step-up transformer: N2 > N1, therefore, V2 > V1

Such a device cannot be used to step up a dc because a dc voltage cannot produce a changing flux, which is very essential to the production of induced emf in the secondary.

❤Sweetheart❤

Answer 2

Explanation:

QUESTION :-

__________

Explain with the help of a labelled diagram the underlying principle and working of a step-up transformer. Why cannot such a device be used to step-up dc voltage ?

ANSWER:-

__________

Step-up transformer (or transformer) is based

Step-up transformer (or transformer) is based on the principle of mutual induction.

(No. of turns, N )

s (No. of turns, ) NP

Input RL Output

ac

Primary coil

Soft iron core

Secondary coil

An alternating potential (Vp) when applied to the

An alternating potential (Vp) when applied to the primary coil induced an emf in it.

Ep = -Np dphi/ dt

If resistance of primary coil is low Vp = ep.

i.e., Vp = -Np dphi/ dt

As same flux is linked with the secondary coil with

the help of soft iron core due to mutual induction

iron core due to mutual induction emf is induced in it.

Es = -Ns dphi / dt

If output circuit is open Vs = es

Vs = - Ns dphi / dt

Thus , Vs / Vp = Ns / Np

For an ideal transformer, Pout = Pin

⇒ IsVs = IpVp

Extra information :-

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Vs / Vp = Ip / Is = Ns / Np

For step-up transformer Ns / Np >1

___________________

In case of dc voltage Flux does not change. Thus no

In case of dc voltage Flux does not change. Thus no emf is induced in the circuit.

Diagram :- see the attachment

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@TheStellar♥️⚡