If the distance between two current carrying parallel wire is made $\left(\frac{1}{3}\right)^{r d}$ then the…
If the distance between two current carrying parallel wire is made $\left(\frac{1}{3}\right)^{r d}$ then the magnitude of the force between them (the same current is passing through both wires)
is tripled.
becomes 6 times.
becomes q times.
remains same.
Solution
Force between wires is inversely proportional to the separation between them,
$F \propto \frac{1}{d}$
Therefore, if the separation between wires becomes $\left(\frac{1}{3}\right)^{r d}$, the magnitude of force is tripled.