Magnetic fields
4 marks · NormalA teacher wants to use plotting compasses to map the magnetic field around a single bar magnet.
Describe the steps the teacher should follow to plot a single magnetic field line using plotting compasses.
What does the direction of a plotting compass needle show about the magnetic field?
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.
Show answer
(a) — · must show Place compass near magnet, Mark dot at end of compass needle, Move compass so tail is at the previous dot, Repeat to trace the path, Join dots to show field line
(b) The direction of the compass shows the direction of the magnetic field (from north to south pole). · must show Shows direction of magnetic field
Common mistakes: Not describing step-by-step method
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Positions compass near the bar magnet and marks the direction of the needle.
M2 (a) · 1 mark · Moves compass so that the tail is at the last dot and repeats marking to trace a path.
A1 (a) · 1 mark · Joins marked dots to show the field line.
B1 (b) · 1 mark · States that the compass shows the direction of the magnetic field.
Worked solution
a) Place a bar magnet on a piece of paper and put a plotting compass near one end. Mark the position of the tip of the needle with a dot. Move the compass so its tail is at the dot, and mark the tip again. Repeat this several times. Finally, join the dots to create a field line.
b) The direction of the compass needle shows the direction of the magnetic field at that point (from north to south outside the magnet).