Explain how the behaviour of a magnetic compass is related to evidence…

The idea

A compass needle is a small magnet that is free to turn. Its north-seeking pole points roughly towards the Earth's geographic north wherever you stand, in either hemisphere, so the needle aligns with a magnetic field that surrounds the Earth. That field must come from somewhere inside the planet, which is evidence that the Earth's core behaves as a magnet. The needle does not flip direction between hemispheres; it still points roughly north. A compass also shows the field direction at any location, and the consistent alignment across the globe supports a magnetic core rather than a local effect.

What earns the marks

• States that a compass needle is a small magnet that turns to align with a magnetic field.
• Explains that the needle's north-seeking pole points roughly north in both hemispheres, showing a field around the Earth.
• Concludes that the Earth's field must originate inside the planet, giving evidence that the core is magnetic.
• Describes how the consistent alignment of compasses at different places supports a magnetic core.

Common mistakes and how to put them right

• Claims the needle flips direction in the opposite hemisphere.

  Put it right: State that it still points roughly north.

• Treats the compass as detecting gravity.

  Put it right: Explain that it aligns with a magnetic field.

• Says the field comes from the surface rocks only.

  Put it right: Link the field to the Earth's core as the source.

Exam tips

• Link each observation of the needle to the inference about the Earth's core.
• Use the phrase 'north-seeking pole' to show which end of the needle you mean.
• Keep the explanation to cause and evidence: field observed, therefore magnetic core.