Here is a rotating magnet inside some coil tubes: I recently learned about Faraday's law. Here since the bulb lights, there must be a changing magnetic flux inducing a current throught the bulb. Where is the magnetic flux changing? To me, the magnetic field does not change throught the whole circular area enclosed by the big loops. However, if the loops are empty tubes, then yes, there is a changing magnetic flux throught the area enclosed by each small cross section of each tube. BUT shouldn't the currents profuced then be running along the small cross sections circumferences of each tube, rather than along the length of the tubes? But if the bulb lights, the induced current must go along the length of the tubes! So my questions are basically : where is the magnetic flux is changing and in what direction goes the induced current in the above picture?