The humming sound that can sometimes be heard near live electric wires is often caused by a phenomenon called "magnetostriction." Magnetostriction refers to the slight changes in shape or dimensions that occur in ferromagnetic materials when subjected to a magnetic field.
Here's a simplified explanation of how it relates to the humming sound:
Alternating Current (AC): Most power distribution systems use alternating current, where the direction of the current periodically reverses. This alternating current creates a fluctuating magnetic field around the wires.
Magnetic Field Interaction: When the alternating current flows through the wires, it generates a magnetic field that surrounds them. This magnetic field interacts with the nearby materials, including the wire itself and any other metallic objects in close proximity.
Magnetostrictive Effect: The alternating magnetic field causes the wire's core, often made of a ferromagnetic material such as iron or steel, to experience minute changes in its dimensions due to magnetostriction. These changes can occur rapidly, corresponding to the frequency of the alternating current.
Vibration and Sound: The magnetostrictive changes in the wire's dimensions can result in mechanical vibrations within the wire. These vibrations can propagate through the wire and other connected objects, such as supporting structures or nearby objects, producing audible sound waves in the process. The resulting humming sound is a manifestation of these vibrations.
It's important to note that the humming sound is generally more noticeable when you are in close proximity to the wire or when the ambient noise levels are low. The exact loudness and characteristics of the sound can also depend on factors such as the voltage and current levels, the type of wire, the installation setup, and the surrounding environment.
If you encounter a persistent or unusually loud humming sound from an electrical wire or any electrical equipment, it's essential to have it inspected by a qualified electrician to ensure there are no underlying issues or potential safety concerns.