Question

a step down transformer is used on a 1000V line to deliver 20A at 120V at the secondary coil. if the efficeincy of the transformer is 80% the current drawn from the line is

1) 3A

2) 30A

3) 0.3A

4) 2.4A

Answer 1

$$\begin{gathered} Efficiencyofthetransfromer=\frac{poweroutput}{powerinput}\times 100 \\ \frac{80}{100}=\frac{V_2{I}_2}{V_1{I}_1} \\ \frac{80}{100}=\frac{120\times 20}{1000\times I_2} \\ {I}_1=3A \end{gathered}$$