Generated by claude-sonnet-4-6 · 2026-06-15 06:48 · grounding rag
Model Answer
(i) Solenoid:
A solenoid is a long coil of wire consisting of a large number of closely wound circular turns of insulated copper wire.
Magnetic field pattern:
(Diagram description for drawing in exam:)
Draw a rectangular coil with many loops. Inside the solenoid, draw straight, parallel, equally-spaced horizontal lines → this is the uniform field region. Outside, draw curved lines from one end to the other (like a bar magnet).
- (i) Direction of current: Mark current going into the page on top of each loop and out of the page at the bottom (using × and •).
- (ii) Direction of field lines near ends: Field lines emerge from the North end (right) and enter the South end (left), curving outward.
- (iii) Uniform field region: Inside the solenoid, along the central axis — field lines are parallel and equally spaced.
The field of a current-carrying solenoid is similar to that of a bar magnet.
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(ii) Making an Electromagnet:
Place a soft iron core (rod) inside the current-carrying solenoid. The magnetic field of the solenoid magnetises the soft iron core strongly, producing a powerful electromagnet. It loses magnetism when the current is switched off.
Source: Chapter 12, Section 12.2
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Explanation
- For (i), examiners expect the definition, a labelled diagram (the most important part), and all three marked features. Even if you cannot draw perfectly, label arrows for current direction (× and •), field line direction at ends, and bracket the uniform region inside.
- For (ii), the key phrase is soft iron core — without mentioning the core material, you lose the mark. Also note that soft iron is preferred over steel because it loses magnetism easily when current stops.
- The solenoid-as-bar-magnet analogy is a standard examiner's expectation.