# 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 load. What is the efficiency of the transformer?

Discussion:

14 comments Page 1 of 2.
Ricky said:
1 decade ago

How did you calculate it?

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%

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

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

Yogeshwaran said:
1 decade ago

Nice explation sir.

Kalai said:
1 decade ago

Good solution.

Anuj Kumar said:
1 decade ago

I don't know this formula whish is used to calculate P out?

So please help me.

So please help me.

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

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

Shibli said:
1 decade ago

Nice explanation.

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.

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.

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.

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.

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