The Earth’s Magnetism (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note
Exam code: 8465
Written by: Katie M
Updated on
Compasses
A magnetic compass contains a small bar magnet
The Earth has a magnetic field
The compass needle points in the direction of the Earth's magnetic field
On Earth, in the absence of any magnet or magnetic materials, a magnetic compass will always point north
This is evidence that the core of the Earth is magnetic
The Earth's magnetic field is similar to that of a bar magnet
The north arrow of a compass points towards the geographic North Pole (Arctic Ocean)
The geographic North Pole is actually a magnetic south pole
Field lines point into the pole
The north pole of the compass is attracted to the Earth's magnetic south pole
The geographic South Pole (Antarctica) is actually a magnetic north pole
Field lines point out of the pole
The north pole of the compass is repelled from the Earth's magnetic north pole
Examiner Tips and Tricks
The Earth's geographic North Pole acts like the south pole of a magnet. That's why the north pole of a compass needle is attracted to it.
A compass needle moves near a magnet because the needle is itself a small permanent magnet, not simply because it is made of metal. Saying 'it is metal' will not score marks.
The Earth's Magnetic Field
The Earth's magnetic field is probably caused by movements in the liquid, iron-rich part of the outer core of the Earth
These movements mean the magnetism of the core is dynamic (changing), not static (fixed)
Evidence for this comes from changes in the field over time:
The positions of the magnetic north and south poles change slowly over time
The field reverses its direction from time to time
The intervals between reversals are not uniform
The last reversal happened about 800,000 years ago
Examiner Tips and Tricks
When asked what causes the Earth's magnetic field, your answer must refer to the liquid, iron-rich outer core, not the mantle, crust, or inner core. The inner core is solid, so it cannot generate the field.
When asked for evidence that the Earth's magnetic field changes over time, do not refer to climate change, the Moon, tectonic plates, or animal migration. The correct evidence is the reversal of field direction and the shift in positions of the magnetic poles over time.
When asked why the Earth's magnetic poles change position, do not refer to climate change, the Earth's tilt, or solar flares. The answer must refer to the dynamic movement of liquid iron in the outer core.
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