Final answer:
The coil in a potential relay is connected between terminal 2 and another specified point, not clearly defined in the provided information, for proper voltage measurement and switching control.
Step-by-step explanation:
In the context of a potential relay, the coil is typically connected between terminals 2 and a reference point or another terminal specified by the relay's design. The information provided does not specify the other terminal. However, typically, potential relays are components used in electrical engineering for starting motors, and they usually have their coils connected between two specific points to allow for the correct measurement of voltage, and to control the switching of the relay based on the voltage levels. The system described, where current is reversed through automatic switches like brushes to keep the coil rotating, relates to electric motors and electromagnetic induction, which includes concepts such as mutual inductance and magnetic fields, as indicated by the references to coils, magnetic field lines, and transformer equation.