Science (086) — AI-generated practice question

Similarity: In both cases, the magnetic field lines form concentric circles around each small element of the wire, and the field strength decreases as distance from the wire increases.

Difference: Around a straight wire, the field lines are concentric circles in planes perpendicular to the wire with no single direction. At the centre of a circular loop, the field is unidirectional (all field lines point the same way — either into or out of the loop).

Why circular geometry gives uniform, unidirectional field at centre:
By the right-hand rule, every section of the circular loop contributes magnetic field lines in the same direction at the centre. The arcs of the large concentric circles from each part of the wire all appear as parallel straight lines at the centre, so all contributions add up in one direction, producing a uniform, unidirectional field there.

Source: Chapter 12, Section 12.2.3 — Magnetic Field due to a Current through a Circular Loop

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• Examiners award 1 mark each for similarity, difference, and the explanation of why the circular loop produces a uniform field — stick to this structure.
• The key phrase to use is "every section of the wire contributes in the same direction" — this comes directly from the textbook and is what examiners look for.
• Don't confuse "uniform" (same at all points) with "unidirectional" (same direction) — at the centre of a single loop the field is unidirectional and approximately uniform, unlike the varying concentric-circle pattern of a straight wire.