Q130 / 200 · NEET 2010 (Screening) · Physics

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

  • A
    $3.6 \mathrm{~A}$
  • B
    $2.8 \mathrm{~A}$
  • C
    $2.5 \mathrm{~A}$
  • Correct answer
    D
    $5.0 \mathrm{~A}$

Solution

Efficiency is defined as the ratio of output power and input power $$ \text { ie, } \begin{aligned} \eta \% & =\frac{\mathrm{P}_{\text {out }}}{\mathrm{P}_{\text {in }}} \times 100=\frac{\mathrm{V}_s \mathrm{i}_s}{\mathrm{~V}_{\mathrm{p}} \mathrm{i}_{\mathrm{p}}} \times 100 \\ 80 & =\frac{2 \times 440}{220 \times \mathrm{i}_{\mathrm{p}}} \times 100 \\ \Rightarrow \quad \mathrm{i}_{\mathrm{p}} & =5 \mathrm{~A} \end{aligned} $$

Hence, the correct answer is option: 'D'.

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