it was a time when cats could party on TV. Compared with LCD screens, old-fashioned picture tube televisions and computer monitors always look particularly bulky. Nowadays, few people use these antiques anymore, but they are still a good example of physics learning that can help people understand the motion of electrons in a magnetic field.

how does the old TV work? In the past, explanations probably depended on schematics, but today we can first look at a physical picture-- in high-speed photography, of course, which looks quite different from what the human eye sees.

first of all, the picture under 2500fps:

you can see that in fact, each part of the screen will not appear at the same time, but constantly "scan" back and forth from top to bottom, but such a "scan" is carried out very quickly, and in the eyes of the human eye, a complete image can be formed through a visual temporary.

and this doesn't really show all the details yet. You can only see more in ultra-high-speed photography: the scan of each line from left to right.

(you can refer to the time shown above, this process really happens very quickly, and the whole process shown in this moving picture takes only a few milliseconds)

the core component of these old televisions is a cathode ray tube. the resulting electrons deflect to a specific position on the screen in a magnetic field to make it glow. The color picture tube TV has three electron guns that emit electrons at the same time, corresponding to the red, green and blue fluorescent agents on the screen (pictured below).

and this way of controlling the electron beam to "hit" a certain point on the screen also determines that there is no way for the whole screen to light up at once, so under high-speed photography, we can see the point-by-point scanning process from top to bottom, from left to right.

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of course, the commonly used display screen no longer uses electron beam, so it does not need to be scanned point by point, and the whole screen can be kept intact all the time.

below is a dynamic picture of the picture tube with a strong magnet to really feel the deflection of the electrons.

original video: https://www.youtube.com/watch?v=3BJU2drrtCM&t=197s

I have to specifically talk about the The Slow Mo Guys trench in the original video inhumanely using high-speed photography from 1600 to 380000fps! It's really inhumane, my friends.