What determines the magnitude of the magnetic field surrounding a conductor?

The magnitude of the magnetic field surrounding a conductor is directly related to the magnitude of the current flowing through it. According to Ampère's circuital law, the magnetic field generated around a straight conductor is proportional to the current that flows through the conductor. As the current increases, the magnetic field strength also increases, and this relationship is foundational in electromagnetism.

For instance, in a long straight wire carrying a steady current, the magnetic field forms concentric circles around the wire, with the strength of the field decreasing with distance from the conductor. Thus, understanding the current’s role in generating the magnetic field is crucial for applications in electromagnetic theory and technology, such as in electric motors and transformers.

While the voltage applied and the resistance of the conductor can influence the current, they do not determine the magnetic field strength directly. Similarly, the length of the conductor affects the distribution of the field but does not alter the intrinsic relationship between current and magnetic field strength. Therefore, the current's magnitude is the key factor determining the size of the magnetic field surrounding a conductor.