Final answer:
The trigger knob on an oscilloscope is used to stabilize the display of a sine wave by setting the starting point of the waveform, resulting in a steady and clear representation of the signal's characteristics.
Step-by-step explanation:
The trigger knob on an oscilloscope plays a critical role in stabilizing the display of a sine wave or any other repetitive signal. It sets the starting point of the waveform on the oscilloscope screen, which helps in providing a steady image. Without proper triggering, the sine wave could appear to be a moving or unstable display, making it difficult to analyze its characteristics. In essence, the trigger function synchronizes the horizontal sweep of the oscilloscope with the signal, ensuring that each sweep starts at the same point of the signal. This consistent starting point allows the waveform to be drawn in the same position on the screen with each pass, giving the appearance of a stable and static sine wave.