Two long conductors separated by a distance 'd' carry currents ' \(\mathrm{I}_1\) ' and ' \(\mathrm{I}_2\) ' in the same directions. They exert a force ' F ' on each other. The distance between them is increased to ' 3 d '. If new repulsive force of magnitude '2/3 F' is found between these conductors, the required change in the magnitude and direction of one of the currents in the conductor is respectively [length of the conductors is constant]

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.