MAGNETIC FIELDS
4 marks · NormalA student investigates the magnetic field around a bar magnet using plotting compasses.
Describe how the student should use plotting compasses to show the direction of the magnetic field around the bar magnet.
State what is meant by a magnetic field line and explain what information about the field is provided by the direction and spacing of the lines.
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 several plotting compasses around the bar magnet on paper. The needles of the compasses will align with the magnetic field at each point, showing the direction of the field at different locations. · must show plotting compass arrangement, alignment indicates direction
(b) A magnetic field line is a line drawn to represent the direction of the magnetic force at each point in the field. The direction of the line shows the direction a north pole would move (from north to south). The closer the lines, the stronger the field. · must show definition of field line, direction from N to S, spacing shows strength
Common mistakes: Not mentioning that compasses indicate direction from north to south; Incorrectly stating that field lines indicate direction from south to north
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly describes placing plotting compasses around the magnet.
B2 (a) · 1 mark · Mentions that compass needles align with field direction at each place.
B3 (b) · 1 mark · Defines magnetic field line as showing direction of magnetic force.
B4 (b) · 1 mark · Explains that direction is north to south and spacing shows field strength.
Worked solution
a) The student places a bar magnet on a sheet of paper and arranges several plotting compasses around the magnet. Each compass needle aligns tangentially to the field lines at its location, so mapping out the needles shows the field direction around the magnet.
b) A magnetic field line is an imaginary line that shows the direction of the magnetic force at various points in the field. The arrows point from the magnet's north pole to its south pole. The closer together the lines, the stronger the field at that region.