Explain, giving reasons, why a current-carrying solenoid behaves like a bar magnet. Draw the field lines of both.

1. 1 · Each turn is a dipole. A turn carrying current I is a loop with magnetic moment IA, along the axis.
2. 2 · The moments add. All N turns point the same way, so m = NIA; one end acts as N and the other as S.
3. 3 · Same field. The outside pattern and the far-axis field, (μ₀/4π)(2m/r³), match those of a bar magnet (result only).
4. 4 · Draw both. [Bar magnet and solenoid side by side with similar closed field lines; N and S marked; current arrows on the turns]
5. 5 · Real life. An electromagnet on a scrap-yard crane is a solenoid with an iron core.
6. 6 · Close in one line. So, a solenoid is an equivalent bar magnet whose poles follow the current.

Scoring tip: Use the words 'each turn is a magnetic dipole' and 'moments add'. Then let the two sketches do the rest.