Question

A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are :

• A. $450V$ and $15A$
• B. $200V$ and $1A$
• C. $400V$ and $9A$
• D. $250V$ and $8A$

Answer 1

The correct option is A $450V$ and $15A$

$\begin{array}{c}{P}_{in}=I_p{V}_p\Rightarrow T_p=\frac{P_{in}}{V_p}=\frac{3000W}{200N}=15A\\ Efficciencyofthetransformer\\ \eta =\frac{P_{out}}{P_{in}}=\frac{V_s{I}_s}{V_p{I}_p}\Rightarrow \frac{90}{100}=\frac{6V_s}{3000}\\ V_s=\frac{90\times 5000}{100\times 6}=450V\end{array}$

Hence,

option $\left(A\right)$ is correct answer.