A resistor of \(40~\Omega\) is connected to the secondary of a step-down transformer, with an input voltage of \(200~\text V\) and an output of \(20~\text V\) across the secondary.
The resistance as seen in the primary circuit is: (ignoring power losses)
1. \(40~\Omega\)
2. \(4~\Omega\)
3. \(0.4~\Omega\)
4. \(4~\text k\Omega\)