Electronics - Transformers - Discussion

Discussion Forum : Transformers - General Questions (Q.No. 2)
2.
A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10 omega.gif load. What is the efficiency of the transformer?
88%
90%
92%
95%
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
14 comments Page 1 of 2.

Sarika said:   1 decade ago
Input power = 120*3*0.001 = 36.
Output current = v/r = 18/10 = 1.8.

Output power = 18*1.8 = 32.4.

n% = O/P power / I/P power = (32.4/36)*100.
= 0.90*100.
= 90%.

Thank you.
(1)

Ece said:   1 decade ago
Should it be that both voltage and current in the primary must be in rms? what if they were in average value? or what if the other one is rms and the other one is average?

Ramesh said:   1 decade ago
Input watt 120*.3(V*I) = 36.

Output watt :
So I = V/R(18/10) = 1.8.

18*1.8 = 32.4 watt.

Eff = output/input.

32.4/36 = 0.90.

So the answer is B.

Karpagamdevu said:   1 decade ago
Formula for P out:

We know that p=v.i --->1
and i=v/r --->2
sub 2 in 1

So p=v*(v/r)
Hence (v^2)/r

Viyoo said:   10 years ago
Pin = 120*0.3=36W.
Pout = 18*18/10=32.4.

efficiency = Pin/Pout.
= (32.4/36)*100.
= 90%.

Ramkumar said:   1 decade ago
pin= v*i = 120*.3 = 36

pout = v^2/R = 18^2/10 = 32.4

eff = pout/pin = 32.4/36 = .9*100 = 90%

NAINA said:   10 years ago
Pin = v.i = 120*0.3 = 36.

Pout = v*(v%r) = 18*(18/10) = 32.4.

n% = op/inp = 32.4/36 = 90%.
(1)

Anuj Kumar said:   1 decade ago
I don't know this formula whish is used to calculate P out?

So please help me.

V seenivasan said:   8 years ago
Fantastic explanation, Thank you all.

Ammu said:   8 years ago
Superb and helpful explanations.


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