Tesla coils are fascinating. These electrical transformers generate a high voltage – complete with lightning bolts and the smell of ozone. Due to their low power, however, the light show is usually harmless, and Tesla coils have become crowd pullers in museums and at science shows.

Yanis Strüby and Silvio Müller, who are in the third year of their apprenticeship as physics laboratory technicians at Empa, shared this fascination. They decided to build a Tesla coil for the «Züri-Oberland» apprentice competition (LWZO). But lightning alone was not enough for the Empa lab technicians-to-be: Their coil should also play music. Last November at the LWZO in Wetzikon, they not only impressed the expert jury, but also their fellow competitors, the other apprentices – and won both the jury and the participant award.

The road to victory was anything but easy. The project had to be researched, planned, calculated, manufactured and tested. The apprentices wound the actual coil by hand: almost 2,000 turns, a total of around 350 meters of copper wire. "We had to be very careful because the wire was very thin and we didn't want it to break," recalls Müller. "It was the first big project of our own and certainly a test of patience," adds Strüby. "But we made it – and we learned that we work very well together under pressure."

Their vocational trainer, Dominik Bachmann, research engineer in Empa's Transport at Nanoscale Interfaces laboratory, encouraged the apprentices to participate at the LWZO – but the idea of the singing Tesla coil, Bachmann stresses, was entirely theirs. "At times, I had to read up on it myself before I could answer their questions," he smiles.

The senior apprentices at Empa were also a source of inspiration to Strüby and Müller: Sofie Gnannt and Nick Cáceres won the LWZO as well as other competitions last year. "These competitions are a cool experience for the apprentices – and good preparation for their individual practical work, one of the requirements to complete their apprenticeship," says Bachmann. Strüby and Müller also enjoyed the exchange with apprentices from various professions. They have already warmly recommended participation in the competition to junior apprentices at Empa.

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