Properties of an electric transformer

Electricity and Magnetism Level 1

The above is a schematic diagram of an electric transformer, where the primary AC voltage is $220\text{ V}$ and the secondary coil is connected with an electric heating instrument. The secondary voltage and current intensity are $110\text{ V}$ and $8\text{ A},$ respectively. Which of the following statements is correct?

There is no energy loss in this electric transformer.

$a)$ The current intensity flowing in the primary winding is $4\text{ A}.$
$b)$ The number of turns in the secondary winding is twice as many as that in the primary winding.
$c)$ The primary coil always transfers $880\text{ W}$ of electric power to the secondary coil without reference to any heating instrument.

a) and b) c) only a) only b) only

3 solutions

Moemen Adel
Oct 21, 2014

i think a) and c) are correct as Pp=I V=4 220=880W

Mohd Naim Mohd Amin
Apr 7, 2014

Hello,

by using V(primary) / V(secondary) = I(secomdary) / I(primary)

as given V(primary) = 220V , V(secondary)= 110V , I(primary) = ? , I(Secondary)=8A

by using the formula,

V(primary) / V(secondary) = I(Secondary) / I(Primary)

220 / 110 = 8 / I(Primary)

I(Primary)= 8/2 = 4A,therefore(1st statementt is true),

as for 2nd statement,

by using the same formula,

V(Primary) / V(Secondary) = N(Primary) / N(Secondary)

220 / 110 = N(Primary) / N(Secondary)

2 /1 = N(Primary) / N(Secondary)

N(Primary) = 2N(Secondary)

Therefore,the 2nd statement is wrong...

For the 3rd statement,

P(Primary) = I(Primary) x V(Primary) = 4 x 220 = 880 Watts

should be correct this one as it is an ideal transformer,but there's no oprion for this,

Therefore,the best is a).the 1st statement.....

Thanks...

Wonder why a and c is not an option for the answer?

As far as I can figure, Power in= Power out P=IV Therefore, IV (in)= IV (out) Putting in the numbers proves A. B is wrong because it should be half, not twice the primary coil. But what about C?? Isn't P=IV, therefore it should be 880W on both sides, since it's an ideal transformer?

I mean, yeah, A and C isn't there. But, with options A only and C only, that confused me quite a bit. I would have had no trouble if A & C were there, but this actually made me do some reading up before I answered, cause I thought I had my facts wrong. Or maybe, C is wrong. And I don't know why. Does anyone know? Please let me know. Thanks. Cheers.

Kevin Mano - 6 years, 9 months ago

Kamal Ahmed
Mar 17, 2014

Vp/Vs=Is/Ip=Np/Ns

Properties of an electric transformer

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