Question

5. A step-down transformer is employed to
reduce the main supply of 220V to 11V.
The primary draws 5 A of current and the
secondary 90A. What is the efficiency of
the transformer?
a) 20% b) 40% c) 70%
c) 70% d) 90%
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Answer 1

Answer:

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Answer 2

Answer:

Answer is D.

The efficiency of a transformer can be calculated using Equation,

Efficiency=  Output power of the transformer/ Input power of the transformer

                =Ps/Pp*100

In this case, the output power is calculated as follows.

The output voltage is 11 V and current is 90 A

Power=VI=11×90=990W.

The input power is calculated as follows.

The input voltage is 220 V and current is 5 A

Power=VI=220×5=1100W.

So, η=  990 /1100  ×100=90%.

The efficiency of the transformer is 90%.