Magnetic field lines
- CBSE · NCERT Class 10, Ch 12 Magnetic Effects of Electric Current
Magnetic field lines are the lines drawn around a magnet or a current-carrying wire to show the direction and strength of its magnetic field.
Iron filings sprinkled near a bar magnet line up along these lines. A small compass placed on a line points along it. The rules to remember:
- Outside a magnet, the lines leave the north pole and enter the south pole.
- They are closed curves: inside the magnet they run from south to north.
- Where the lines are closer together, the field is stronger.
- Two lines never cross. At a crossing a compass would point two ways, which cannot happen.
Around a straight wire carrying current, the lines are circles centred on the wire. The right-hand thumb rule gives their direction.
A small example
Place a compass 2 cm from a straight wire and switch on the current. The needle turns. Increase the current and it turns more. Move the compass to 6 cm away and it turns less. The field grows with current and falls with distance.
Where marks go
Question 36(B) of CBSE's 2026-27 Science sample paper asks how the field changes with distance from a straight wire. The 2026-27 Science marking scheme gives 1 mark for stating that it decreases as you move away.
A question can mark three points beside a wire and ask where the field is strongest, and why. The answer is the nearest point, with the reason given. See how to write answers the scheme can mark.
Sources
Facts last checked against these sources on 30 September 2026.
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