Question

A $220$ volt input is supplied to a transformer. The output circuit draws a current of $2.0$ ampere at $440$ volts. If the efficiency of the transformer is $80\%$, the current drawn by the primary windings of the transformer is

• A. 3.6 ampere
• B. 2.8 ampere
• C. 2.5 ampere
• D. 5.0 ampere

Answer 1

Answer: (D)

Here,
Input voltage, $V_p=220V$
Output voltage, $V_s=440V$
Input current, $I_p=$ ?
Output current, $I_s=2A$
Efficiency of the transformer, $\eta =80\%$
Efficiency of the transformer, $\eta =\frac{\text{ Output power }}{\text{ Input power }}$
$\eta =\frac{V_s{I}_s}{V_p{I}_p}$
or $I_p=\frac{V_s{I}_s}{\eta V_p}=\frac{(440V)(2A)}{\left(\frac{80}{100}\right)(220V)}$
$=\frac{(440V)(2A)(100)}{(80)(220V)}$
$=5A$