The Barkhausen effect

https://youtu.be/BLXVLDysroY

"When a ferromagnetic material like iron gets exposed to a magnetic field, it gets magnetized in a very large number of little "jumps". With a coil of wire and audio amplifier, these "jumps" can be converted to an audio signal in a phenomenon known as the Barkhausen effect. Here I do a short demonstration of the effect with a variety of materials in a coil of wire, in anticipation of a future blog post."