What types of modulation does a CRT operate by?

A cathode-ray tube (CRT) operates primarily through intensity and deflection modulation. Intensity modulation refers to the adjustment of the electron beam's brightness as it strikes the phosphorescent screen, creating images with varying degrees of brightness. This modulation is crucial for displaying different colors and shades in the images, as the intensity of the beam directly affects how bright or dark a pixel appears on the screen.

Deflection modulation involves controlling the direction of the electron beam as it travels across the screen. The beam is deflected using magnetic or electrostatic fields, allowing it to sweep across the phosphor surface in a controlled manner. By varying the horizontal and vertical deflection signals, the CRT can create the desired image by directing the electron beam to specific locations on the screen.

Both types of modulation are essential for the CRT to function effectively, enabling dynamic and accurate image rendering. The other options do not accurately capture the primary functions of a CRT, focusing instead on modulation techniques that are either not applicable or secondary in nature to the workings of a CRT.