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How is a Magnetic Field Just an Electric Field with Relativity Applied?

Time: Mar 26, 2024 Hits: 1

The interrelations of electric fields and magnetic fields are one of the basic ideas in physics, and this concept is closely connected to the theory of relativity. In this article I will explain how it can be possible that magnetic field can be considered as an electric field on which relativity applies.

Electric Fields and Magnetic Fields

Electric fields come from electric charges, they also exert forces on other electric charges while magnetic fields emit out from moving electric charges and these ones act upon other moving charges too.

Special Theory of Relativity

The special theory of relativity has two postulates: that the laws of physics are invariant under Lorentz transformations between inertial reference frames (i.e. they are covariant), and that the velocity of light in vacuum is constant irrespective of any motion or source of light.

Relativity and Electromagnetism

However, when considering electromagnetism with respect to these principles as applied by Einstein’s theories on relativity, we find out that this process demonstrates two separate aspects known as electromagnetic fields – namely electric field and magnetic field. A magnetic field may appear like an electric field in another frame depending on whether the observer or the source is in motion relatively to each other.

Magnetic Field as a Relativistic Electric Field

Let us consider a positively charged particle moving inside a wire; in the frame of reference for such wire there exists an electric field around such particle. However if we change into the view point coming from a running object then neutral atoms within wire begin to move while negatively charged particles seem more densely packed due to length contraction (a consequence brought about by special relativity). Consequently, there exists an electrical field when viewed against its stationary frame but appears as magnetism within it.


To conclude, a magnetic field can be understood through relativistic means as an electrical force. This link connecting electricity with magnetism through the theory of relativity not only goes a long way into helping us understand more about electromagnetism but also reveals the profound nature of Einstein’s relativity theory in our perception of physical reality.

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