A solenoid carrying current behaves like a bar magnet, yet the magnetic field inside a solenoid is described as uniform, while the field near the poles of a bar magnet is not. Explain why the field lines inside a solenoid are parallel and straight, and identify ONE way in which the field pattern outside both a solenoid and a bar magnet is similar.
Generated by claude-sonnet-4-6 · 2026-06-26 01:13 · grounding rag
Model Answer
Inside a solenoid, each circular turn produces a small magnetic field. When many such turns are wound closely together, the fields of all turns add up inside, and their effects cancel on the outside. This results in a strong, uniform field with parallel, straight field lines inside the solenoid — indicating equal field strength at all interior points.
Similarity with a bar magnet: The field pattern outside both a current-carrying solenoid and a bar magnet is identical — field lines emerge from the north pole, curve around the outside, and re-enter at the south pole.
Source: Chapter 12, Section 12.2.4 — Magnetic Field due to a Current in a Solenoid
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Explanation
- Examiners expect two things clearly addressed: (1) why the interior field is uniform/parallel — due to superposition of fields from multiple closely-wound turns — and (2) one similarity in the external field pattern.
- The textbook explicitly states: "The field lines inside the solenoid are in the form of parallel straight lines... the field is uniform inside the solenoid" and "one end behaves as north, the other as south" — mirroring a bar magnet's external field.
- Avoid over-explaining; state the cause (additive effect of turns) and the result (parallel lines = uniform field) concisely.
- The similarity point is straightforward: identical external dipole-like field pattern — this scores the third mark.