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A transformer is used to light a $100 \mathrm{~W}, 110 \mathrm{~V}$ lamp from a $220 \mathrm{~V}$ supply. If the supply current is $0.6 \mathrm{~A}$, then the efficiency of the transformer is
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The correct answer is:
$76 \%$
For a transformer,
Input voltage, $V_{1}=220 \mathrm{~V}$
Input current, ${I}_{1}=0.6 \mathrm{~A}$
Output power, $P_{2}=100 \mathrm{~W}$
From, input power, $\quad P_{1}=V_{1} I_{1}$
$$
\begin{aligned}
&=220 \times 0.6 \\
&=132 \mathrm{~W}
\end{aligned}
$$
We know that, efficiency of transformer,
$$
\begin{aligned}
\eta &=\frac{P_{2}}{P_{1}}=\frac{100}{132}=0.7576 \\
&=75.76 \% \simeq 76 \%
\end{aligned}
$$
Input voltage, $V_{1}=220 \mathrm{~V}$
Input current, ${I}_{1}=0.6 \mathrm{~A}$
Output power, $P_{2}=100 \mathrm{~W}$
From, input power, $\quad P_{1}=V_{1} I_{1}$
$$
\begin{aligned}
&=220 \times 0.6 \\
&=132 \mathrm{~W}
\end{aligned}
$$
We know that, efficiency of transformer,
$$
\begin{aligned}
\eta &=\frac{P_{2}}{P_{1}}=\frac{100}{132}=0.7576 \\
&=75.76 \% \simeq 76 \%
\end{aligned}
$$
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