A current-carrying solenoid is often described as equivalent to a bar magnet. (i) What does the pattern of magnetic field lines inside a solenoid tell you about the nature of the field there? (ii) Why is this property particularly useful when a solenoid is used to make an electromagnet?
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
(i) The field lines inside a solenoid are parallel straight lines. This indicates that the magnetic field is uniform (the same in magnitude and direction) at all points inside the solenoid.
(ii) The uniform and strong magnetic field inside the solenoid is particularly useful because when a soft iron core is placed inside, this strong field magnetises it effectively and uniformly, producing a powerful electromagnet. The strength can also be controlled by varying the current.
Source: Chapter 12, Section 12.2.4 – Magnetic Field due to a Current in a Solenoid
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Explanation
- (i) The key phrase examiners want is "parallel straight lines → uniform field." Write both the observation and the conclusion.
- (ii) Link the uniform/strong field to magnetising a soft iron core — that is the direct application stated in the textbook. Mentioning controllability is a bonus point.
- Avoid writing about bar-magnet similarity here unless asked; keep focus on what the question asks.
- For 3 marks, roughly 1 mark per concept: parallel lines, uniform field, usefulness for electromagnet.