Solenoid
- CBSE · NCERT Class 10, Ch 12 Magnetic Effects of Electric Current
A solenoid is a long, tightly wound coil of insulated copper wire, shaped like a tube, that behaves like a bar magnet while current flows through it.
When current flows, one end of a solenoid behaves as a north pole and the other as a south pole. Outside, its field looks like a bar magnet's. Inside, the field lines are parallel straight lines. So the field is the same at every point inside.
Put a piece of soft iron inside and it becomes a strong magnet while the current flows. That is an electromagnet. Switch the current off and the pull stops.
A small example
A solenoid of 100 turns carries 1 A. Raise the current to 2 A and the field inside grows, because the field depends directly on the current. Keep 1 A but wind 200 turns in the same length, and the field grows again. Each turn adds its own field in the same direction.
Where marks go
Question 38 of CBSE's 2026-27 Science sample paper is one of its case-based questions, about a door lock worked by a solenoid. The 2026-27 Science marking scheme gives 1 mark for why an iron core is used: it makes the field stronger. It gives 1 mark for finding the poles.
The last part carries 2 marks. One choice asks what happens when the current rises from 1 A to 2 A. The field grows, so the lock pulls harder. The other asks for two ways to strengthen the field at a fixed current. Examples are more turns or a soft iron core. The scheme's answer to the first choice ends with the effect on the lock.
Sources
Facts last checked against these sources on 30 September 2026.
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