# Magnetic field

## Main Question or Discussion Point

Since we have such a strong magnetic field around the earth, why does it not interfere with smaller magnetic fields we use such as medical equipment, radio wave progagation and other things that creates an magnetic field ???

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K^2
Earth's magnetic field is actually very weak. Also, constant* magnetic field does not interfere with electromagnetic wave propagation in any way.

* In fact, electromagnetism is linear, so an EM wave propagates regardless of what other magnetic and electric fields are present, at least through vacuum, but an oscillating magnetic field would create noise that could potentially cause problems for the receivers.

Hello, its a most common problem regarding the interference of the earth's magnetic field with the other magnet within( or on) the earth's surface. The magnetic effect shown by all the magnets on the earth is the combined (or the already effected) effect of the earth's and the magnet. For instance, the north pole of a magnet points towards the magnetic south pole of the earth. Had there been no magnetic field of the earth; the orientation of the taken magnet would have been opposite! Hence, magnetic fields we use such as medical equipment, radio wave propagation and other things that creates an magnetic field are ALREADY interfered by the earth's magnetic field!

Thank you! This is what I thought but just was not sure. I expermint wih RF and antenna design. I know we have an electrostatic and electromagnatic with radio progragation, and one creates the other. I am the back yard mechanic type, so I have a lot of questions about our magantic field in regarding RF. I guess a good example would be the aroura and 50mhz reflection. This indeed affect RF at this frequency but I did not know about all the rest. Thank you for your input.

You probably know about magnetic dipoles then.

Earth has a huge dipole moment which is approximately centered at the center of the planet. So on the surface you are looking at the magnetic field of a dipole some 6360 km away. The resulting field is quite small, even smaller than that of a common fridge magnet. But fridge magnet has a very small dipole moment, so that when you get a little distance away its field will have dropped to below the earth's field.

Charged particles from the sun or elsewhere have to travel thousands of km through this field, so the integrated effect is pretty large.

There are some experiments such as electron spectroscopy that are disturbed by the earth's magnetic field. But as the field is static, it is easy to put a small coil around the experiment and tune the current until the earth's field is cancelled.