6 · IGCSE Physics
Magnetic field patterns
Set up one bar magnet or two magnets that attract or repel, then move a plotting compass around to map the field and compare it with the drawn field lines.
Move the pointer over the field to move the compass. Click (or press Enter) to plot an arrow.
Model: each pole acts like a point source; B ∝ Σ q r̂ / r² (q positive for N, negative for S). The compass needle's N end turns to point along B. Outside a magnet, lines run from N to S; closer lines mean a stronger field.
Try this
- With one magnet and field lines switched off, plot about ten compass arrows around the magnet, then switch the lines on and compare your pattern.
- Choose the attract arrangement and reduce the gap to 2 cm: notice how the lines between the facing poles become straight, parallel and close together (a strong, nearly uniform field).
- Choose the repel arrangement and hunt for the neutral point between the magnets where the field strength readout falls almost to zero and the needle barely settles.
Exam tip: draw field lines as smooth curves with arrows pointing from N to S outside the magnet, never let two lines cross, and draw them closer together where the field is stronger.