In a cathode ray tube, which part becomes luminous when struck by an electron beam?

• A. An electron gun
• B. An electron counter
• C. A CRT screen
• D. An electron amplifier

Answer: (C)

In a cathode ray tube, the part that becomes luminous is the screen. The inside of the screen is coated with phosphor. The electron beam from the electron gun is directed and accelerated to strike this phosphor layer. When the high-energy electrons hit the phosphor, their energy excites the phosphor atoms and they emit light as they return to their ground state, producing the visible glow that forms the image. The electron gun itself provides the electrons but doesn’t glow; the other components aren’t responsible for light emission in this context.