Question

A step-down transformer with an efficiency of $80\, %$ is used on a $1000\, V$ line to deliver $10\, A$ at $100\, V$ at the secondary coil. The current drawn from the line is

• A. 1.5 A
• B. 2 A
• C. 3 A
• D. 1.25 A
• E. 1 A

Answer 1

Answer: (D)

Given, $ \eta=80 \%, \, V_{\text {in }}=1000\, V ,\, l=10 \,A$ and
$V=100\, V$
Output power
$P_{\text {out }}=I \times V$
$P_{\text {out }}=10 \times 100$
$ P_{\text {out }} =1000 \,VA $
and $P_{\text {in }} =\frac{P_{\text {out }}}{\eta}=\frac{1000}{0.8} \,VA $
$ I_{\text {in }} =\frac{P_{\text {in }}}{V_{\text {in }}}=\frac{1000}{0.8 \times 1000}$
$I_{\text {in }} =1.25\, A$