A student uses a plotting compass to investigate the magnetic field of the Earth. The student notices that the compass needle always points in the same direction when placed on a flat surface away from any magnets or iron objects. Explain what this tells us about the Earth, and describe how the magnetic field of the Earth compares to that of a bar magnet.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
The Earth behaves as a magnet, producing a magnetic field.
The compass needle aligns with this field and points towards the geographic north pole, which is actually the magnetic south pole of the Earth.
The field lines emerge from the Earth’s magnetic south pole (near the geographic north) and enter at the magnetic north pole (near the geographic south), curving around the planet.
The overall field has the same dipole shape as a bar magnet, with lines curving from one pole to the other.
Unlike a small bar magnet, the Earth’s field extends far into space and is spread over a very large area, making it much weaker at any given point but covering a much larger volume.
The compass needle aligns with this field and points towards the geographic north pole, which is actually the magnetic south pole of the Earth.
The field lines emerge from the Earth’s magnetic south pole (near the geographic north) and enter at the magnetic north pole (near the geographic south), curving around the planet.
The overall field has the same dipole shape as a bar magnet, with lines curving from one pole to the other.
Unlike a small bar magnet, the Earth’s field extends far into space and is spread over a very large area, making it much weaker at any given point but covering a much larger volume.
Examiner tips
- Show the Earth is a magnet and the needle points to geographic north. Explain the direction of field lines and the dipole shape. Mention the large scale and weaker intensity compared to a bar magnet.
Common mistakes
- Confusing geographic north with magnetic north. Saying the field is stronger than a bar magnet. Forgetting that the field lines enter at the geographic north pole.
Mark scheme (5 marks)
- The Earth behaves as / acts like a magnet (has a magnetic field)
- The compass needle points towards the Earth's geographic north (pole) / the compass aligns with the Earth's magnetic field
- The Earth's magnetic field has field lines that (travel from south to north / enter at the geographic north pole / exit at the geographic south pole) OR the geographic north pole is near the Earth's magnetic south pole
- The Earth's magnetic field is similar in shape to that of a bar magnet / has field lines that curve from one pole to the other
- The Earth's magnetic field extends into space / is much weaker than a bar magnet's field OR the Earth's field is large-scale / spread over a much greater area than a bar magnet
Key terms in this question
magnetic field · plotting compass
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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