Function of X plates in cathode ray oscilloscope?

Answer 1

1. cathode - emits electrons which will become the beam
2. control grid - adjustment of beam current and thus brightness on screen
3. focus grids - focusing beam to sharp point on screen to form small dot
4. x plates - deflect beam left/right
5. y plates - deflect beam up/down
6. anode - aquadag coating (baked on graphite applied in water suspension) on the inside of the CRT's cone, both accelerates the beam and collects the electrons that rebound from the screen

Note: the grids in a CRT are different from the grids in ordinary vacuum tubes: in a CRT the grids are just round holes in metal disks that surround the beam, in ordinary vacuum tubes the grids are actual wire grids in the direct path of electron flow.

Answer 2

The X plates deflect the electron beam in the horizontal direction. The plates set up a potential electric field across the beam path. This bends the e-beam. This is electrostatic deflection.