 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2022/ib/paper-2/16d/b/i/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

By cylindrical symmetry the field is azimuthal and constant on a circle of radius

r

. The Ampère's law for a steady current gives

2 π r B = μ_{0} I,

B = \frac{μ _{0} I}{2 π r} e_{ϕ} .

In the plane

x = 0

with

y > 0

, it points in the

- x

direction.

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