Measuring the speed of light with electric and magnetic pendulum
  This problem was given at the Fourth Open and International Experimental Physics Olympiad (EPO4) Day of Light on 23 April 2016 in Sofia organized by the Sofia Branch of the Union of Physicists in Bulgaria and the Society of Physicists of the Republic of Macedonia, Strumica. 
Vasil G. Yordanov, Vassil N. Gourev, Stojan G. Manolev, Albert M.   Varonov, and Todor M. Mishonov
physics.ed-ph