AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Explain how the behaviour of a magnetic compass is related to evidence…
Full specification wording
Magnetic fields: explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.
A magnetic compass contains a small magnet that is free to rotate.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 8 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A magnetic compass contains a small magnet that is free to rotate. It always settles with its north-seeking pole pointing roughly towards the Earth's geographic north. This happens because the Earth behaves as though a giant bar magnet is inside it, producing a magnetic field that exerts a turning force on the compass needle. The compass aligns with the local field line, so its direction indicates the field direction at that place. Because the needle responds wherever it is used on the Earth's surface, the field must originate within the Earth. The only plausible source is the Earth's core, so the core must be magnetic. The field is not exactly aligned with the rotation axis, which is further evidence that it comes from the core rather than from the Earth's rotation alone.
What earns the marks
- A compass needle is a small magnet that is free to rotate and aligns with the local magnetic field.
- The needle consistently points approximately north-south wherever it is used on the Earth's surface.
- The Earth's magnetic field must originate from a magnetic core, because the field is present everywhere on the surface.
- The magnetic poles are close to, but not exactly at, the geographic poles, which supports the idea of a magnetic source inside the Earth rather than a rotational effect.
Common mistakes and how to put them right
Saying the compass is attracted to the geographic North Pole.
Put it right by explaining that the compass aligns with the Earth's magnetic field, whose south magnetic pole is near geographic north.
Claiming the compass needle points to the Earth's core.
Put it right by stating that the needle aligns with the field at its location, and the field's origin is the core.
Confusing magnetic poles with geographic poles.
Put it right by noting that the magnetic axis is tilted relative to the rotation axis, so compass north differs slightly from true north.
Exam tips
- Link each observation to a conclusion: compass behaviour leads to the idea of an Earth-wide field, which leads to a magnetic core.
- Use the phrase 'north-seeking pole' rather than just 'north pole' to avoid ambiguity.
- Mention that the field is present at all locations on the Earth's surface, which rules out a local cause.
Try the lesson
The start of the Magnetic fields: explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic. lesson, made from checked teaching notes for this specification point.
Have a go first
A student holds a magnetic compass away from any magnets and notices that its needle always comes to rest pointing in the same direction. What does this show about the Earth?
Listen
A magnetic compass contains a small magnet that is free to rotate. It always settles with its north-seeking pole pointing roughly towards the Earth's geographic north. This happens because the Earth behaves as though a giant bar magnet is inside it, producing a magnetic field that exerts a turning force on the compass needle. The compass aligns with the local field line, so its direction indicates the field direction at that place. Because the needle responds wherever it is used on the Earth's surface, the field must originate within the Earth. The only plausible source is the Earth's core, so the core must be magnetic. The field is not exactly aligned with the rotation axis, which is further evidence that it comes from the core rather than from the Earth's rotation alone. A strong answer earns marks for these points. A compass needle is a small magnet that is free to rotate and aligns with the local magnetic field. The needle consistently points approximately north-south wherever it is used on the Earth's surface. The Earth's magnetic field must originate from a magnetic core, because the field is present everywhere on the surface. The magnetic poles are close to, but not exactly at, the geographic poles, which supports the idea of a magnetic source inside the Earth rather than a rotational effect. A common slip: Saying the compass is attracted to the geographic North Pole. Instead, explaining that the compass aligns with the Earth's magnetic field, whose south magnetic pole is near geographic north. Exam tip: Link each observation to a conclusion: compass behaviour leads to the idea of an Earth-wide field, which leads to a magnetic core.
Key words
Say what each word means before you turn the card.
magnetic compass
Try answering aloud or in your head before turning the card.
Earth's magnetic field
Try answering aloud or in your head before turning the card.
magnetic core
Try answering aloud or in your head before turning the card.
See every definition
- magnetic compass
- Contains a small magnet that is free to rotate and always settles with its north-seeking pole pointing roughly towards the Earth's geographic north.
- Earth's magnetic field
- Produced as though a giant bar magnet is inside the Earth, exerting a turning force on a compass needle so it aligns with the local field line.
- magnetic core
- The only plausible source of the Earth's magnetic field, because the field is present everywhere on the surface.
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