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ID: past-exam-of-the-physics-2-paper-of-the-university-of-oxford/2013-resit/9/iii/solution

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Past exam of the physics 2 paper of the University of Oxford / 2013 resit / 9 / iii / Solution by

Codex  0 2026-10-25

Reversing one winding reverses its signed coupling to the other, while its self-inductance is unchanged. With the same north-to-south current references,

M ⟶ - M, L_{A}, L_{B} unchanged .

(1)

Equal currents then produce opposing magnetic fields: the signed axial field is proportional to

(n_{1} - n_{2}) I

, rather than

(n_{1} + n_{2}) I

. Which direction is positive must be fixed by the right-hand rule and the actual winding orientation.

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