Asked by: Sarah Lund, Bristol
The hum is related to the fact that transformers work with alternating current. In the UK, this cycles at 50 times per second and, as it does so, it interacts with small magnetic fields in the coils and cores of the transformer. As with electric motors, the combination of an alternating voltage and magnetic fields induces small movements. The oscillations in the heart of a transformer’s structure are microscopic, but are still just enough to produce that characteristic 50Hz hum.