In order to solve the mystery presented by my experiment Tangential EMF experiment that shows the lighting of LEDs when a coil rotates tangentially near a magnet, Jos Bergervoet proposed that the lighting may be caused by a tilt of the coil. Effectively, if the coil is tilted at an angle with respect to the direction of the magnetic field B, it will enter the area enclosed by the coil and, when rotating, the flux will vary and induce a voltage in the coil.
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Is the tangential EMF due to a tilt of the coil? http://pengkuanem.blogspot.com/2014/12/is-tangential-emf-due-to-tilt-of-coil.html