Verified Solution • 2025–26 Session moderate

QPages 249-253: Q28: HC Verma: Concepts of Physics - Volume 2 Magnetic Field Due to a Current Pages 249-253: Q28 Solution: Two parallel wires separated by a distance of 10 cm carry…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently assume the zero-force point lies outside the wires or fail to verify that the magnetic fields oppose each other; for parallel currents, the null point is always between the wires, and the distance is proportional to the current magnitude ($x \propto I$), not inversely proportional.

Two parallel wires separated by a distance of 10 cm carry currents of 10 A and 40 A along the same direction. Where should a third current be placed so that it experiences no magnetic force?

Step-by-Step Verified Solution

**Answer:** 2 cm from the 40 A wire (between the wires). **Step-by-Step Explanation:**

i_1 = 10

A,

i_2 = 40

A, separation = 10 cm. For zero force,

B_1 = B_2

:

\frac{\mu_0 \times 10}{2\pi x} = \frac{\mu_0 \times 40}{2\pi (0.1 - x)}

.

10(0.1 - x) = 40x \Rightarrow 1 - 10x = 40x \Rightarrow x = 0.02

m = 2 cm from the 10 A wire.

All Questions in this Chapter

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