Question

The ratio of secondary and primary turns of step-up transformer is $4:1$. If a current of $4A$ is applied to the primary, the induced current in secondary will be

• A. 8 A
• B. 2 A
• C. 1 A
• D. 0.5 A

Answer 1

Answer: (C)

In a step up transformer, the output voltage from the secondary transformer is increased in the ratio of number of coils in the primary and secondary.
Thus $\frac{V_{\text{secondary }}}{V_{\text{primary }}}=\frac{4}{1}$
Since the power $VI$ should remain the same,
$$\begin{gathered} V_{\text{primary }}{I}_{\text{primary }}=V_{\text{secondary }}{I}_{\text{secondary }} \\ <br/>\Rightarrow \frac{I_{\text{secondary }}}{I_{\text{primary }}}=\frac{V_{\text{primary }}}{V_{\text{secondary }}} \end{gathered}$$
$=\frac{1}{4}$
$\Rightarrow I_{\text{secondary }}=1A$