What are magnetic poles and fields, and how do they behave?
Magnets and magnetic fields: permanent and induced magnets, attraction and repulsion between poles, magnetic field patterns, and the Earth's magnetic field.
A focused answer to AQA GCSE Physics 4.7.1, covering permanent and induced magnets, the forces between magnetic poles, the shape of magnetic field patterns, magnetic materials, and the use of a compass and the Earth's magnetic field.
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What this dot point is asking
AQA wants you to distinguish permanent from induced magnets, describe the forces between poles, draw and interpret magnetic field patterns, identify magnetic materials, and explain how a compass shows the Earth's magnetic field. This is part of topic 4.7.1 of the AQA GCSE Physics (8463) specification.
Permanent and induced magnets
Forces between poles
Every magnet has two poles, a north-seeking pole and a south-seeking pole, and these always come in pairs: you cannot have a single isolated pole. If you cut a bar magnet in half you simply get two smaller magnets, each with its own north and south pole. The force between poles is one of the non-contact forces, acting through the magnetic field that surrounds each magnet, which is why two magnets can push or pull on each other across a gap.
The magnetic materials are iron, steel, cobalt and nickel; only these are attracted by a magnet. This is why most metals, such as copper, aluminium and gold, are not attracted to a magnet at all, a fact often used to identify materials. The distinction between attraction and repulsion is a reliable test for whether something is itself a permanent magnet: two objects that sometimes attract and sometimes repel (depending on orientation) must both be magnets, because only a magnet can be repelled, whereas a magnetic material that is not itself magnetised can only ever be attracted.
Magnetic fields
The Earth's magnetic field and compasses
Try this
Q1. State what happens when two north poles are brought close together. [1 mark]
- Cue. They repel each other (like poles repel).
Q2. Explain the difference between a permanent magnet and an induced magnet. [2 marks]
- Cue. A permanent magnet always produces its own field; an induced magnet is only magnetic while in a magnetic field and loses it when removed.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20184 marksExplain the difference between a permanent magnet and an induced magnet, and describe how a steel paperclip can become an induced magnet and pick up a second paperclip.Show worked answer →
A permanent magnet produces its own magnetic field all the time and keeps its magnetism (1 mark). An induced magnet only becomes magnetic when it is placed in a magnetic field, and it loses most or all of its magnetism when removed from the field (1 mark). When a steel paperclip is brought near a permanent magnet, it is placed in the magnet's field and becomes an induced magnet, gaining its own north and south poles (1 mark). The now-magnetised paperclip can then attract a second paperclip, which itself becomes induced; induced magnetism always causes attraction, never repulsion (1 mark). Markers reward the permanent-versus-induced distinction, the loss of magnetism on removal, and that induced magnetism only attracts.
AQA 20213 marksDescribe the magnetic field pattern around a bar magnet, and explain how a plotting compass provides evidence that the Earth has its own magnetic field.Show worked answer →
The magnetic field of a bar magnet is shown by field lines that run from the north pole to the south pole outside the magnet, curving around from one pole to the other (1 mark). The field is strongest where the lines are closest together, which is at the poles (1 mark). A plotting compass contains a small bar magnet that is free to turn and lines up with whatever magnetic field it is in; in the open it settles pointing roughly north, which shows there must be a magnetic field acting on it, namely the Earth's own magnetic field produced by its core (1 mark). Markers reward the north-to-south direction of the lines, the field being strongest at the poles, and the compass alignment as evidence for the Earth's field.
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Sources & how we know this
- AQA GCSE Physics (8463) specification — AQA (2016)