Purpose:Show that electromagnetic theory obeys a relativity principle.
Description:Measure the current (qualitatively) in a coil when the coil and a bar magnet are in relative motion. Einstein (1905) complained that the standard conceptualization (electric forces if the magnet moves, magnetic forces if the coil moves) seems more convoluted than the phenomenon which appears the same whichever component is "at rest." In the links below, a coil is moved onto the north pole of a stationary magnet and the north pole of a moving magnet is inserted into a stationary coil. The bottom row of photos shows the reverse setup, with a coil moved onto the south pole of a magnet, and the south pole of a moving magnet inserted into a stationary coil.