Hey Alice!
So they are applied ever so slightly differently. Are you okay with the Physics behind how the deflection plates actually work? Let me know if you aren't, but assuming you are, it's all about what external signal the horizontal and vertical deflection plates are aligned to.
In Oscilloscopes, the horizontal deflection is controlled by a time varying signal. This causes the beam to sweep horizontally across the screen, from left to right, at a constant pace. The vertical deflection is controlled by some other signal, a measurement (for example, a microphone). What this creates is a vertical axis dependent on signal strength of some stimuli, and a horizontal axis dependent on time. Think of your typical heartbeat monitor in the hospital drama shows, that is exactly what I'm talking about
In Cathode Ray Televisions, both the horizontal and vertical deflection plates have time varying strengths. The idea here, put simply, is that it makes the electron beam sweep across the entire television screen. It sweeps along the top row of phosphor dots (kind of like pixels on your laptop), then the second row, then the third row, so quick that you just see the solid image.
There are 3 electron guns in Colour CRT's, each corresponding to either Red, Green, or Blue. Each is tasked with creating a specific colour on the screen (there are different phosphors, one for each colour). The intensity of each is controlled with a separate accelerating anode
This explanation is definitely lacking a bit in certain areas, there is some pretty complex stuff involved, but this is a good overview. Is there any specific part of this that is a bit iffy for you?
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On top of Jamon's flawless answer, it might also be worth mentioning that Cathode Ray Oscilloscopes (CRO) use electric fields as their deflection plates and TVs use magnetic fields. CROs use electric fields as they can switch at higher frequencies than magnetic fields (so it can basically respond to the stimuli faster whereas magnetic fields take a bit longer) and TVs use magnetic fields because when they deflect the electron beam, they deflect it in a circular path (the force is perpendicular to the direction of motion of the electron beam (from right hand palm rule), which means it provides a centripetal force and therefore, circular motion) whereas electric fields deflect in a parabolic path. So then the radius of curvature is greater and therefore, the TV can have a bigger screen (CROs don't need a massive screen) !! But yeah, the electron gun functions the same way for both (i.e. both have heating filament at cathode, which 'boils' off electrons through thermionic emission, which then goes through control electrode, focussing anode and accelerating anode before reaching the deflection plates) and its just the different fields used by the deflection plates
If you wanted a few more advantages and disadvantages between electric plates and electromagnetic coils (magnetic fields), here they are:
Electric platesAdvantages-Can respond at higher frequencies (mentioned above)
-Less power required for deflection
Disadvantages-Needs to be inside the tube in order for the field to be strong enough (this complicates the tube design)
-Deflects in parabolic path (lower radius of curvature)
-Larger defocussing during deflection (longer tube is required)
Electromagnetic coilsAdvantages-Smaller defocussing of the electron beam when deflecting
-Deflects in a circular path, therefore greater radius of curvature (reduces length of cathode ray tube needed for a bigger screen size)
-Can be positioned outside the tube (simplifies tube design)
Disadvantages-Requires more power to operate
-Harder to get uniform magnetic field
I was just studying this yesterday so feel free to correct me if I stuffed up somewhere!!