Why can't two magnetic field lines cross each other ? Draw magnetic field lines showing the direction of the magnetic field due to a current carrying long straight solenoid. State the conclusion which can be drawn from the pattern of magnetic field lines inside the solenoid. Name any two factors on which the magnitude of the magnetic field due to this solenoid depends.
Generated by claude-sonnet-4-6 · 2026-06-15 06:50 · grounding rag
Model Answer
Why two magnetic field lines cannot cross each other:
At any point in a magnetic field, there can be only one direction of the field. If two field lines crossed, it would indicate two different directions of the field at that point, which is impossible. Hence, field lines never intersect.
Magnetic field lines of a current-carrying solenoid:
(Diagram: parallel, equally-spaced straight lines inside the solenoid, with closed loops outside, one end labelled N and the other S)
Conclusion from the pattern inside the solenoid:
The field lines inside are parallel and equally spaced, indicating that the magnetic field is uniform (same in magnitude and direction) at all interior points.
Two factors on which the magnitude of the magnetic field depends:
- The number of turns in the solenoid
- The magnitude of current flowing through it
Source: Chapter 12, Section 12.2.4
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Explanation
- Crossing lines (1 mark): Examiners want the reason "only one direction possible at a point" — state it clearly.
- Diagram (1 mark): Draw neat parallel lines inside and curved closed loops outside; label N and S poles.
- Conclusion (1 mark): The key word is uniform — must mention both same magnitude and same direction.
- Two factors (2 marks, 1 each): Number of turns and current strength are standard textbook answers. Nature of core material is also acceptable as a third (not needed here).
- Keep the answer focused; do not confuse solenoid factors with those for a straight wire.