Creating a uniform magnetic field
4 marks · NormalA student wants to demonstrate a uniform magnetic field using two permanent bar magnets in a simple classroom experiment.
State how the bar magnets should be positioned to create a region of uniform magnetic field.
Suggest one way, apart from iron filings, the student could check that the field is uniform.
The student tries to move a small piece of iron slowly through the region between the poles. Predict what will happen to the piece of iron and explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Place magnets so their opposite poles (north and south) are facing each other, with a small gap between them.
(b) Use multiple plotting compasses. If the compass needles all point in the same direction and form parallel alignments throughout the region, the field is uniform.
(c) The piece of iron will be attracted toward the nearest pole of the magnets. This happens because the strong field between the poles induces magnetism in the iron, causing it to move towards areas of stronger field (towards the poles).
Common mistakes: Not stating both opposite poles and small gap; Not explaining attraction to poles;; Not describing compass or field shape
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Marking points
B1 (a) · 1 mark · States opposite poles facing each other with a gap between magnets.
B2 (b) · 1 mark · Mentions plotting compasses aligning uniformly as an indicator of field uniformity.
B3 (c) · 1 mark · States iron is attracted towards poles or region of stronger field.
B4 (c) · 1 mark · Explains this as due to induced magnetism or attraction to stronger field areas.
Worked solution
a) Place the bar magnets with their N and S poles facing each other, a small gap between them. b) Use several plotting compasses. If the needles point in the same direction and are parallel across the region, it indicates a uniform field. c) The piece of iron will experience a force pulling it toward the poles of the magnets because the strong field induces magnetism in it, and it is attracted to stronger field regions.