Question

the principal of working of a transformer is

Answer 1

Here is your answer....
A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.
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Answer 2

principal of transformer

Transformer works on the principal of Faraday law of electromagnetic induction .

Working of transformer

When alternate voltage V(t) given to transformer that is

V(t)= V(m) Sin (\omega *t)

or

V(t)= V(m)cos(\omega *t)

which produced current

I(t)= i(m) sin(omega *t)

or

I(t)= i(m) cos(\omega *t) .

Transformer contain inductor coil of total number of coil is N then there must produced MMF(Megneto motive force )So

=>MMF = NI(t)

There must produced flux due to MMF where flux

$flux = \frac{mmf}{r}$

where r is called reluctance

so

$r = \frac{l}{ ua}$

where

u is called permeblity

a is called area

and

flux = maximum flux *Sin(\omega \:t)

Due to Faraday law of electromagnetic induction these flux induced secondary coil of transformer in that way voltage were regulated by transformer .