Question

How much current is drawn by the primary coil of a transformer which steps down $220V$ to $22V$ to operate a device with an impedance of $220\Omega$ ?

• A. 1 A
• B. 0.25 A
• C. 0.01 A
• D. 1.50 A

Answer 1

Answer: (C)

Here, ${\epsilon }_p=220V,{\epsilon }_s=22V$\
and $Z=220\Omega$ If $i_s$ is the current through the secondary, then
$i_s=\frac{{\epsilon }_s}{Z}=\frac{22V}{220\Omega }=0.1A$
We know that, ${\epsilon }_p{i}_p={\epsilon }_s{i}_s$
where, $i_p$ is the current drawn by the primary coil
Thus, $220\times i_p=22\times 0.1A$
$\Rightarrow i_p=0.01A$