Q1. [3] § 12.2.2 Right-Hand Thumb Rule § 12.2.4 Magnetic Field due to a Current in a Solenoid
(B) For the current carrying solenoid as shown, draw magnetic field lines and give reason to explain that out of the three points A, B and C, at which point the field strength is maximum and at which point it is minimum ?
Previously asked in CBSE board exam
2023 31/4/1 Q32 (B)
Generated by claude-sonnet-4-6 · 2026-06-15 06:49 · grounding rag
Model Answer
Magnetic Field Lines of a Solenoid:
The field lines inside the solenoid are parallel and straight (uniform field), while outside they resemble the field of a bar magnet — spreading out from the poles and looping around.
Field Strength at A, B, and C:
- Point B (inside the solenoid) — field strength is maximum. The field lines inside are parallel and closely packed, indicating a strong, uniform magnetic field.
- Point A (just outside, near the end/pole) — field strength is moderate, as field lines are less concentrated.
- Point C (far outside the solenoid) — field strength is minimum, because field lines spread out widely and are far apart, indicating a weak field.
Reason: Field lines are shown closer together where the magnetic field is greater. Inside a solenoid, they are densest; far outside, they spread the most.
Source: Magnetic Field due to a Current in a Solenoid, Chapter 12
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Explanation
- Examiners expect a labelled description of field lines (parallel inside, bar-magnet pattern outside) — even without the diagram, describe it clearly.
- The key principle to cite: closer field lines = stronger field; this is stated directly in the textbook.
- Typically, B is inside (maximum), and the farthest external point is minimum. Adjust A/B/C labels to match your diagram if positions differ.
- Always link your answer to the reason — "because field lines are closer/farther apart" — to earn the reasoning mark.
If a question refers to an image, map, graph or diagram that is not shown here, find the actual CBSE question paper on the CBSE website:
cbse.gov.in.