The Earth behaves like a giant bar magnet due to the movement of molten iron within its core. This creates a global magnetic field that protects the planet and allows for navigation.
A magnetic compass needle is a small permanent magnet that aligns itself with the Earth's magnetic field. Because the North pole of a compass is attracted to the Arctic, the Earth's geographic North Pole is actually a magnetic South Pole.
Evidence for the Earth's magnetic core is provided by the fact that a freely suspended magnet or compass will always align itself in a North-South direction regardless of
The shape and direction of a magnetic field can be mapped using a plotting compass. This method involves placing a magnet on paper and marking the direction the compass needle points at various positions.
By moving the compass so the tail of the needle aligns with a previously marked dot at the head, a series of points is created. Connecting these dots results in a smooth curve representing a magnetic field line.
This process must be repeated starting at different points around the magnet to build a comprehensive map of the entire field structure.
| Feature | Permanent Magnet | Induced Magnet |
|---|---|---|
| Source | Internal alignment of domains | External magnetic field |
| Duration | Persistent | Temporary (lost when field removed) |
| Force | Can attract or repel | Always attracted to a magnet |
| Materials | Steel, Neodymium | Iron, Nickel, Cobalt |
Directional Accuracy: When drawing field lines, always ensure arrows point from North to South. A common mistake is drawing them in reverse or having them touch/cross, which is physically impossible.
Field Strength Representation: Ensure lines are closest together at the poles to demonstrate that the magnetic force is strongest there. As you move away, the spacing should increase significantly.
Uniform Fields: If asked to draw a uniform field between two poles, use a ruler to ensure lines are perfectly parallel and use a compass to ensure they are equally spaced.
Testing for Magnets: Remember that attraction is not a definitive test for a magnet (as a magnetic material will also be attracted). Only repulsion between two objects proves that both are permanent magnets.
