Magnetic Speed

I asked a question about the speed of propagation of a magnetic feild.?

It seems that the word "spread" caused confusion. Thus, for example, suppose a powerful electromagnet has been established on Mars, the magnetic field can be detected / measured on Earth. What I want to know is how long would it take, once the solenoid is activated on the feild be detected on Earth and that speed can be determined mathematically

The magnetic force field term involves the application of a force on a distant object, say a piece of iron by a magnetic field. To generate a magnetic field that can be said to spread, it is necessary to produce an evolving field by turning on an electromagnet or removing a magnet from a magnetic shield as a superconductive region. Modified magnetic fields are also produced in all radio transmitter antennas due to changes in current flow. When a magnetic field evolves, it is always accompanied by a transverse electric field, ie, it is an electromagnetic wave. The relationship between changes magnetic and electric fields are summarized in the well known Maxwell's equations. The speed of electromagnetic waves is known and is certainly defined as exactly 299,792,458 m / s in vacuum (same as the speed of light).

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