A magnet is made to oscillate with a particular frequency, passing through a coil as shown in figure. The time variation of the magnitude of e.m.f. generated across the coil during one cycle is

When north pole of magnet approaches the one face of coil, then the face of the coil becomes a north pole to oppose this motion and current flows anticlockwise. Thus, in this case emf is developed in the coil and when it completes one half motion it is momentarily at rest and no emf is present. Now south pole approaches the other face of coil making this face a south pole. The current now flows in clockwise direction and
again an emf is developed in the coil. This variation is shown in figure (1).