Final answer:
The suspended charged metal plate in the presence of a fixed charged plate will move due to the electric field between them, experiencing either attraction or repulsion based on the relative charges of the plates.
Step-by-step explanation:
When two electrically charged metal plates are positioned with one fixed and one suspended, allowed to move, the interaction between the charges will lead to a force being exerted on the plates. This is due to the electric field that is established between the plates when one is connected to the positive terminal of a battery and the other to the negative terminal, creating a uniform electric field between them as described in Figure 18.28. The suspended plate will experience an attractive or repulsive force depending on the nature of its charge relative to the fixed plate.
If the suspended plate has a charge opposite to that of the fixed plate, it will be attracted towards the fixed plate, due to the attractive force between opposite charges. This attraction continues until the plates either come into contact or are stabilized by another force. Conversely, if the suspended plate has the same type of charge as the fixed plate, it will be repelled, and the plate will move away from the fixed plate until an equilibrium position is reached or the force is counteracted.
The concept of charges moving in unison, like 'a tube of marbles' or a 'train and its carriages,' helps us visualize the movement of charges within a conductor, where individual charges are not distinguishable, but their overall movement is directed by the forces exerted upon them by the electric field, as illustrated with the charged spheres and metal balls in various figures and discussions.