Question

What is the purpose of Aquadag coating in Cathode Ray Tube?

• A. To maintain non-uniform electric field inside the tube
• B. To collect the electrons after they hit the screen
• C. To improve voltage
• D. To improve sensitivity

Hint:

Think of Aquadag as an "electronic vacuum cleaner." Its main job is to "suck up" the loose secondary electrons to keep the inside of the tube clean and functional.

Answer 1

The Correct Option is B

1. The Secondary Emission Problem: When high-speed electrons from the beam strike the phosphor screen, they cause the emission of "secondary electrons" from the screen's surface. If these electrons were allowed to accumulate, they would create a negative space charge, eventually repelling the primary beam and causing a "charging effect" that distorts the image.

2. Function of the Aquadag Coating: The Aquadag coating is connected to a high positive potential (the final anode). It acts as a

collector for these secondary electrons. By providing a path for these electrons to return to the circuit, it prevents charge buildup and ensures the tube interior remains electrically neutral and vacuum-stable.

3. Additional Roles:

• It helps in forming an electrostatic shield to protect the beam from external electrical interference.

• It assists in maintaining a uniform accelerating field near the screen area.