A student constructs a model geophone (a device used to detect ground vibrations) as shown in the diagram below.
A lightweight plastic cylinder with a copper wire coil wrapped around it is suspended by a spring over a strong cylindrical permanent magnet fixed to the stand's base. The coil's ends are connected to a sensitive center-zero galvanometer.
Explain how the student can use this apparatus to demonstrate the factors that affect both the size and the direction of the induced electromotive force (emf).