Creating a uniform magnetic field
3 marks · NormalExplain, with reference to field lines, why the region just outside the gap between two opposite magnet poles is not uniform, even when the gap itself is.
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Also accept: Outside the gap, the field lines curve and spread apart, so the field strength and direction change from place to place. Only between the poles are the lines parallel and evenly spaced.
Common mistakes: Saying field is constant outside the gap; Not describing field shape or spacing.
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Marking points
B1 · 1 mark · States the field lines outside the gap are curved or splay outwards.
B2 · 1 mark · Explains that spacing between the field lines changes outside the gap.
B3 · 1 mark · States that change in line spacing/direction means changing field strength/direction (non-uniform).
Worked solution
The magnetic field is only uniform in the region between the opposite poles, where field lines are straight and parallel. Just outside the gap, the lines curve outward and become non-parallel and unevenly spaced, making the field strength and direction variable — so the field is no longer uniform there.