GITAM, Department of Engineering Physics
Magnetostriction
Why does the
transformer hum?
You may have
noticed the humming sound associated with a transformer or a fluorescent light
ballast. For U.S. circuits, that hum will be at 120 Hz since the iron material
associated with the transformer core responds mechanically to the magnetic
field which is impressed upon it. The effect is called magnetostriction, and
it is one of the magnetic properties which accompanies ferromagnetism. For 60
Hz applied magnetic fields in AC electrical devices such as transformers, the
maximum length change happens twice per cycle, producing the familiar and
sometimes annoying 120 Hz hum.