Fluoroscopy – Physics Practice Test

In a television camera tube, the image information is carried by modulating the electron beam as it scans the target. The light from the scene hits a photosensitive (or photoconductive) target, and the brightness at each point causes the target’s electrical properties to change. As the electron beam sweeps across, these changes affect the current that flows when the beam hits the target, producing a video signal that varies in time in proportion to the image brightness. So the beam is described as being modulated—the current it produces varies with the scene—rather than remaining constant, being blanked, or only being deflected for scanning.