Do you know that the Earth is also a magnet? Yes!!! How do you think then that the suspended bar magnet always points in the north-south direction? Adware about the concept of the Terrestrial Magnetism that we are going to discuss in this chapter. It is really interesting to study and analyze this concept of earth’s magnetism.
The branch of Physics which deals with the study of earth's magnetic field is called terrestrial magnetism.
- William Gilbert suggested that earth itself behaves like a huge magnet. This magnet is so oriented that its S pole is towards geographic north and N pole is towards the geographic south.
- The earth behaves as a magnetic dipole inclined at small angle $11.5^{\circ}$ to the earth's axis of rotation with its south pole pointing geographic north.
- The idea of earth having magnetism is supported by following facts.
- A freely suspended magnet always comes to rest in N-S direction.
- A piece of soft iron buried in N-S direction inside the earth acquires magnetism.
- Existence of neutral points. When we draw field lines of bar magnet we get neutral points where magnetic field due to magnet is neutralized by earth's magnetic field.
- The magnetic field at the surface of earth ranges from nearly 30 $\mu T$ near equator to about 60$\mu T$ near the poles. The magnetic field on the axis is nearly twice the magnetic field on the equatorial line.
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