an oscillatory system with two or more degrees of freedom that is a combination of “partial systems,” or systems having one degree of freedom each, that interact with each other. Depending on the character of the oscillations in each of the partial systems, conclusions can be drawn as to certain characteristic features of the oscillations in the coupled system.
An example of a coupled system is two or more oscillatory circuits (Figure 1) in which the oscillations in one circuit induce oscillations in the other circuits because of the presence of a coupling. Energy is transferred from one circuit to another in a coupled system. The presence of the coupling alters the character
of resonance phenomena in a coupled system as compared with a single isolated oscillatory circuit. In a coupled system resonance occurs whenever the frequency of the external electromotive force coincides with one of the natural oscillation frequencies of the system. For example, in a coupled system consisting of two circuits, resonance occurs at two different frequencies.