You can do this to enhance or change the magnetic field of the magnet. Core rope memory and such use this principle to read, write and refresh the contents of

You can do this to enhance or change the magnetic field of the magnet. Core rope memory and such use this principle to read, write and refresh the contents of the cores. They send a pulse down one of the lines, read line sends one voltage, write line sends a higher one designed to flip the polarity if necessary, and then sense the reflected pulse on the third wire, called the sense wire.