Question

A step down transformer is used on a $1000$V line to deliver $20$A at $120$V at the secondary coil If the the efficiency of the transformer is $80\%$ the current drawn from the lines is

• A. $3$A
• B. $30$A
• C. $0.3$A
• D. $2.4$A

Answer 1

The correct option is A $3$A

Efficient of transformer $=\frac{Poweroutput}{Powerinput}\times 100$

$\Rightarrow \frac{80}{100}=\frac{V_2{I}_2}{V_1{I}_1}$

$\Rightarrow \frac{80}{100}=\frac{120\times 20}{1000\times \pm 1}$

$I_1=3A$.