Question

The ratio of secondary and primary turns of step-up transformer is $4 : 1$. If a current of $4\,A$ 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,
$V _{\text {primary }} I _{\text {primary }}= V _{\text {secondary }} I _{\text {secondary }} \\ \Rightarrow \frac{ I _{\text {secondary }}}{ I _{\text {primary }}}=\frac{ V _{\text {primary }}}{ V _{\text {secondary }}}$
$=\frac{1}{4}$
$\Rightarrow I _{\text {secondary }}=1\, A$