What physical principle explains the creation of a magnetic field by an electric current?

The creation of a magnetic field by an electric current is explained by the principle of electromagnetism. When an electric current flows through a conductor, it produces a magnetic field around it. This phenomenon is described by Ampère's circuital law, which states that the magnetic field in space around an electric current is proportional to the amount of current flowing through the conductor and is also dependent on the distance from the wire.

The orientation and direction of this magnetic field can be determined using the right-hand rule, which helps visualize how the magnetic field lines encircle the wire. This effect is not just theoretical; it is the basis for many practical applications, such as electromagnets, electric motors, and generators, which utilize the interaction between electricity and magnetism.

Other concepts such as thermodynamics, quantum mechanics, and fluid dynamics do not relate to the relationship between electric currents and magnetic fields. Thermodynamics primarily deals with heat and energy transformations, quantum mechanics focuses on the behavior of particles at atomic and subatomic levels, and fluid dynamics studies the behavior of fluids in motion. Hence, the principle of electromagnetism accurately and comprehensively describes the phenomenon of magnetic field generation by electric currents.