A transformer is used to light a 100W and 110V lamp from 220V mains. If the main current is 0.5 amp, the efficiency of transformer is approximately :

10 %

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50 %

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60 %

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90 %

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Solution

The correct option is D $90 %$
Given,
The mains current is $0.5 A$ .
The mains voltage is $220 V$ .
Power of light $= 100 W$ and voltage $V = 110 V$
The efficiency is $n = \frac{output}{input} \times 100 = \frac{100}{220 \times 0.5} \times 100 = 90.9$
The approximate efficiency of transformer is $90 %$ .
Therefore the correct option is $D$ .

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