Electricity & Megnetism

Ampere’s Law

Ampère formulated Ampère’s Law which determines the magnetic field around a wire carrying an electric current.

One of the most remarkable revolutions in physics was the discovery made by Hans Cristian Oersted, where through his experiments he proved the existence of a magnetic field around a wire when it was traversed by an electric current.

Although Oersted discovered that a wire carrying an electric current generates a magnetic field around it, it was André Marie Ampère who, mathematically, deduced this field. We can say that Ampère’s great achievement was to have developed a famous law called Ampère’s Law.

Ampere’s law, as it became known, established the magnetic field ( ) generated by a straight conductor traversed by an electric current of intensity i , at a distance ( R ) from the conductor.

Mathematically, the magnetic field vector ( ) is determined by the following equation:

Where the term μ is a constant known as the magnetic permeability of the vacuum . For mathematical convenience, this constant has been defined as:

μ = 4π .10 -7 Tm/A

Since this is a conventional value, which can have its infinite number of significant figures because of the value of π, the value below can be adopted for the magnetic permeability of vacuum or air (when expressed with two significant figures):

μ = μ air = 1.3 .10 -6 Tm/A

The direction and direction of the magnetic field vector are given by the right-hand rule, remembering that the vector   is always tangent to the imaginary circles described around the conductor, in perpendicular planes.

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