NEET · Physics · STD 12 - 4. Moving charges and magnetism

Two very long, straight, parallel conductors \(A\) and \(B\) carry current of \(5\,A\) and \(10\,A\) respectively and are at a distance of \(10\,cm\) from each other. The direction of current in two conductors is same. The force acting per unit length between two conductors is: \(\left(\mu_0=4 \pi \times 10^{-7}\right.\) SI unit)

A \(2 \times 10^{-4}\,Nm ^{-1}\) and is attractive
B \(2 \times 10^{-4}\,Nm ^{-1}\) and is repulsive
C \(1 \times 10^{-4}\,Nm ^{-1}\) and is attractive
D \(1 \times 10^{-4}\,Nm ^{-1}\) and is repulsive

Verified Solution

Answer & Solution

Correct Answer

(C) \(1 \times 10^{-4}\,Nm ^{-1}\) and is attractive

Step-by-step Solution

Detailed explanation

\(\frac{ F _{ M }}{\ell}=\frac{\mu_0 i _1 i _2}{2 \pi r }\) \(=\frac{4 \pi \times 10^{-7} \times 5 \times 10}{2 \pi \times 0.1}=10^{-4}\,N / m\)

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.

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