Question

A step-down transformer with an efficiency of $80$ is used on a $1000V$ line to deliver $10A$ at $100V$ 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, $\eta =80\%,V_{\text{in }}=1000V,l=10A$ and
$V=100V$
Output power
$P_{\text{out }}=I\times V$
$P_{\text{out }}=10\times 100$
$P_{\text{out }}=1000VA$
and $P_{\text{in }}=\frac{P_{\text{out }}}{\eta }=\frac{1000}{0.8}VA$
$I_{\text{in }}=\frac{P_{\text{in }}}{V_{\text{in }}}=\frac{1000}{0.8\times 1000}$
$I_{\text{in }}=1.25A$