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A-Level Physics May/June 2025 Q2(c)(ii): With reference to your answer in (b)(ii), describe how the observed magnetic field of t…
A-Level Physics · Paper 9702/42 · May/June 2025 · Question 2(c)(ii) · [3 marks]
With reference to your answer in (b)(ii), describe how the observed magnetic field of the Earth varies around the surface.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
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The Earth's magnetic field can be modelled as that of a large bar magnet. The observed field varies across the surface in the following ways:
- The magnetic field is strongest at the magnetic poles and weakest near the magnetic Equator. This is because the magnetic field lines are most concentrated at the poles and most spread out at the Equator.
- At the magnetic poles, the field lines are perpendicular to the Earth's surface (the angle of dip is 90°).
- Near the magnetic Equator, the field lines are parallel to the Earth's surface (the angle of dip is 0°).
How the marks are awarded
- B1 — Correctly describing the variation in the magnitude (strength) of the magnetic field, stating it is strongest at the poles and weakest at the Equator.
- B1 — Correctly describing the orientation of the magnetic field at the poles, stating that it is perpendicular to the surface.
- B1 — Correctly describing the orientation of the magnetic field at the Equator, stating that it is parallel to the surface.
Common mistakes
- Only describing the variation in strength (e.g., 'stronger at poles, weaker at equator') and not mentioning the direction, thereby missing a potential mark.
- Confusing the properties at the poles and Equator, for example stating the field is parallel at the poles and perpendicular at the Equator.
- Using vague language such as 'the field changes' or 'the angle is different' without specifying how or where.
- Confusing magnetic poles with geographic poles, although this is often tolerated if the physics description is correct.
Examiner tip: For questions about fields, always visualise the field lines and describe both their density (to indicate strength) and their direction relative to a surface or axis.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
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