What phenomenon is created around a conductor when current flows through it?

When current flows through a conductor, it generates a magnetic field around it. This phenomenon is a fundamental principle of electromagnetism known as Ampère's law, which states that moving electric charges (in this case, the electric current) create a magnetic field. The direction of the magnetic field lines can be determined using the right-hand rule, which states that if you wrap your right hand around the conductor with your thumb pointing in the direction of the current, your fingers will curl in the direction of the magnetic field.

This magnetic field can be observed around any conductor carrying current, regardless of its shape or size, and its strength is directly related to the amount of current flowing through the conductor. The creation of this magnetic field is the basis for many electrical devices, such as transformers and electric motors, which rely on the interactions between magnetic fields and electric currents.

The other choices refer to phenomena that do not directly result from the flow of current in a conductor. An electrical field is associated with electric charges, a thermal field relates to heat generation (which can occur due to resistance in the conductor), and an optical field pertains to light, none of which inherently describes what happens around a current-carrying conductor.