Extra · Magnetism · Classes 6–10
Magnetic field of a bar magnet
Objective: To map the magnetic field lines around a bar magnet with a compass.
🧰 Apparatus
- Bar magnet
- Plotting compass
- White sheet
- Pencil
- Iron filings (optional)
📐 Formulas and SI units
field lines: N → S outside the magnet
field strongest where lines are closest
💡 Theory
Magnetic field lines leave the N pole and enter the S pole outside the magnet. A compass needle lines up with the field. Lines never cross, and they are closest where the field is strongest, at the poles.
🪜 Procedure
- Place the magnet on paper and draw its outline.
- Put the compass near the N pole and mark where the needle points.
- Move the compass to that mark and repeat, building a line.
- Draw several lines from different starting points.
- Sprinkle iron filings to check the pattern.
📋 Observations Simulated values
✅ Result and conclusion
The lines curve from N to S; above the middle of the magnet the compass points parallel to the magnet, from N towards S (180° here).
🔬 In a real lab
The Earth's field disturbs the compass far from the magnet; weak magnets give patterns that fade quickly.
⚠️ Safety
Keep magnets away from phones, cards and computers; do not drop them (they can lose magnetism or chip).
❓ Quick check
1. Outside a magnet, field lines go from…
2. Where is the field strongest?
3. Can two field lines cross?
🏋️ Practice
EasyLike poles…?
Answer: Repel
MediumWhich way does a compass point at the N pole?
Answer: Away from the N pole
ChallengeWhat happens if you cut a magnet in half?
Answer: Two smaller magnets, each with N and S