STANDARD Physics Magnetic Force on a Current-Carrying Wire MCQ Question
Two straight wires A and B of lengths 10 m and 12 m carrying currents of 4.0 A and 6.0 A respectively in opposite direction, lie parallel to each other at a distance of 3.0 cm. The force on a 15 cm section of the wire B near its centre is
2.4 × 10⁻⁵ N, attractive
2.4 × 10⁻⁵ N, repulsive
1.2 × 10⁻⁵ N, attractive
1.2 × 10⁻⁵ N, repulsive
Correct Answer
Detailed Explanation
The lengths of the two wires are quite large as compared to the separation between them. The two wires may be regarded as infinitely long wires. The force per unit length of wire B due to A is calculated using the formula f = (μ₀I₁I₂)/(2πd). The force on 15 cm or 0.15 cm section of B is F = f × l = 1.6 × 10⁻⁴ × 0.15 = 2.4 × 10⁻⁵ N (repulsive).
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