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  4. A transformer is used to light a 100 W, 110 V lamp from a 220 V supply. If the supply current is 0.6 A, the efficiency of the transformer is

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Q. A transformer is used to light a $100\, W$, $110\, V$ lamp from a $220\, V$ supply. If the supply current is $0.6\, A$, the efficiency of the transformer is

COMEDKCOMEDK 2015Alternating Current

Solution:

As efficiency of the transformer,
$\eta =\frac{P_{out}}{P_{in}}$
Here. $P_{out} = 100 \, W , \:\: V_{in} = 220 \, V$
$I_{in} = 0.6 \, A$
$\therefore \:\:\: P_{in} = V_{in} \times I_{in} = 220 \times 0.6 = 132 \, W$
So, $\eta = \frac{100}{132} = 0.7576 = 75.76 \% = 76\%$