If a sinusoidal rather than a dc input is applied, the situation will change completely. The varying input will move the instantaneous operating point up and down a region of the characteristics and thus defines a specific change in current and voltage as shown in Fig. 1.25 . With no applied varying signal, the point of operation would be the Q -point appearing on
Fig. 1.25 , determined by the applied dc levels. The designation Q-point is derived from the word quiescent , which means “still or unvarying.”