 Solution

ID: past-exam-of-the-physics-b-course-of-the-university-of-cambridge/2010/paper-2b/section-a/2/solution

Pairing adjacent contributions from the Biot-Savart law gives magnitude

μ_{0} I N (N + 1) / (4 πa)

, directed opposite to the first wire's field at the observation point.

Full derivation: solution.

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