A geophone is a highly sensitive sensor used to detect ground vibrations during seismic activity. It converts mechanical motion into an electrical signal.
Figure 1 shows a simplified cross-sectional diagram of a geophone.
When a seismic wave travels through the ground, the housing and the attached coil of wire vibrate vertically. Due to its inertia, the heavy suspended magnet remains relatively stationary, resulting in relative motion between the coil and the magnet.
Explain why a potential difference is induced across the ends of the coil as the housing vibrates.