Final answer:
The question deals with Physics and the behavior of an electron beam in a cathode-ray tube (CRT) as it interacts with crossed electric and magnetic fields, causing the phosphors on the screen to glow. It is a concept typically studied at the high school level.
Step-by-step explanation:
The subject of the question pertains to Physics, specifically related to the behavior of cathode-ray tubes (CRTs) in the presence of electric and magnetic fields. CRTs use an electron beam that interacts with phosphors on the screen to create visible light. When the beam passes through crossed electric and magnetic fields, the path of the electrons is altered, causing the phosphor to glow in a specific pattern. This principle is used in various applications including older television sets and computer monitors, as well as in other types of electron beam technology such as electron microscopes.
Moreover, the bending of the electron beam by magnetic fields, and the effect on a screen if a magnet is brought near it, are examples of how the behavior of electrons in a vacuum can be visualized and measured. This ties back to fundamental concepts of charge and mass, electromagnetism, and the interactions of particles with electric and magnetic fields.