A $220 \mathrm{~V}$ input is supplied to a transformer. The output circuit draws a current of $2.0…
A $220 \mathrm{~V}$ input is supplied to a transformer. The output circuit draws a current of $2.0 \mathrm{~A}$ at $440 \mathrm{~V}$. If the efficiency of the transformer is $80 \%$, the current drawn by the primary windings of the transformer is
$3.6 \mathrm{~A}$
$2.8 \mathrm{~A}$
$2.5 \mathrm{~A}$
$5.0 \mathrm{~A}$
Solution
Efficiency is defined as the ratio of output power and input power
$\text {i.e, } \begin{aligned}
\eta \% & =\frac{\mathrm{P}_{\text {out }}}{\mathrm{P}_{\text {in }}} \times 100=\frac{\mathrm{V}_s \mathrm{i}_s}{\mathrm{~V}_{\mathrm{p}} \mathrm{i}_{\mathrm{p}}} \times 100 \\
80 & =\frac{2 \times 440}{220 \times \mathrm{i}_{\mathrm{p}}} \times 100 \\
\Rightarrow \quad \mathrm{i}_{\mathrm{p}} & =5 \mathrm{~A}
\end{aligned}$