What is the Electrostatic Lens Effect in Cathode Ray Oscilloscopes?

[Idoubt]

Came across it when I was studying about Cathode ray oscilloscopes, it says that two sets of parallel plates are kept at a high pd with another one of relatively lower pd between them. Then electrons from an electron gun are shot into it. It says that the electrons are focused on the cro's screen by electrostatic lens effect. I've looked up on the effect but I couldn't find any satisfactory explanations.. If someone can give me a clearer picture, I'd appreciate it.

 

[sophiecentaur]

I think the 'high potential' will be a negative one - a positive electrode would attract the electrons, diverging the beam and it may even act as another anode, if the beam diverges enough to hit it. With a negative potential, the ring will repel the electrons in the beam, diverting them towards the beam centre. This, on its own is a crude focusing effect which can be improved to get an actual 'spot' by using more than one ring at different potentials - the field between each ring can be made stronger on the outside and weaker on the inside (further from the gap) and so the outer parts of the beam will be bent more than the inner parts. (Hence the lens analogy) If you get it right, they should all be bent towards the same spot. There is a further problem which an optical lens doesn't suffer from and that is the fact that the electrons actually repel each other. That means you have to try harder (higher potentials) and that the beam will naturally separate after a while.

I guess this is rapidly becoming old technology as we can analyse most time dependent signals in real time (or quasi real time) and then put the result onto a non-CRT display. Shame, in a way, when you think how ingenious the best CRT designs are / were.

 

[astrokreng]

The Electrostatic Lens Effect in Cathode Ray Oscilloscopes is a phenomenon that occurs when a high voltage is applied to two sets of parallel plates, with a third set of plates at a lower voltage in between. This creates an electric field that acts as a lens, focusing the electrons from the electron gun onto the screen of the oscilloscope.

The process begins with the electron gun, which emits a beam of electrons. These electrons are negatively charged and are attracted to the positively charged plates. As the electrons pass through the first set of plates, they are accelerated towards the second set of plates due to the strong electric field. The second set of plates then focuses the electrons even further towards the screen.

The third set of plates, known as the deflection plates, are used to control the position of the electron beam on the screen. By varying the voltage on these plates, the beam can be moved horizontally and vertically, creating the familiar waveforms seen on an oscilloscope.

The Electrostatic Lens Effect is crucial for the proper functioning of a cathode ray oscilloscope. Without it, the electrons from the electron gun would not be focused onto the screen, resulting in a blurry or distorted image. This effect allows for precise control and manipulation of the electron beam, making the oscilloscope a valuable tool for scientists and engineers.

In summary, the Electrostatic Lens Effect in Cathode Ray Oscilloscopes is the use of electric fields to focus and control the electron beam, resulting in a clear and accurate display on the screen.