A transformer is used to light a $100 \mathrm{~W}$ and $110 \mathrm{~V}$ lamp from a $220 \mathrm{~V}$ mains…

A transformer is used to light a $100 \mathrm{~W}$ and $110 \mathrm{~V}$ lamp from a $220 \mathrm{~V}$ mains. If the main current is $0.5 \mathrm{amp}$, the efficiency of the transformer is approximately.
  1. $50 \%$
  2. $90 \%$
  3. $10 \%$
  4. $30 \%$

Solution

The efficiency of transformer
$\begin{aligned}
\eta & =\frac{V_s I_s}{V_p I_p} \times 100 \\
& =\frac{100}{220 \times 0.5} \times 100=90 \%
\end{aligned}$

Asked in: NEET 2007

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