The Earth’s magnetic field is three dimensional in the same way as the field of any magnet. It is because of the Earth’s 3D magnetic field that the magnetic needle of a compass has to be weighted so that it floats horizontally in one hemisphere; but this means that the weight is on the wrong end of the needle for the other hemisphere, so that it doesn’t work there. The vertical component of the Earth’s magnetic field can be shown by a dip needle (constrained to rotate in a vertical plane) or a freely-rotating Magnaprobe TM.
Many more activities about the Earth's magnetism can be found on the website.
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