My physics textbook states an activity- "Cut out thin strips of paper and lightly iron them. Take them near a TV screen or computer monitor. The strips get attracted to the screen and may cling to the screen for a while." But this doesn't happen in practice. Is this because I did the activity with an lcd screen. Will a crt/led/plasma screen make it happen? If so, why? Why should the paper strips be ironed?
2
-
1$\begingroup$ Your textbook is probably from the age when crt screens were more prevalent. That works best with them. Also, if you have access to a crt screen, don't forget to degauss it a few times just for fun $\endgroup$– JimCommented Apr 1, 2015 at 14:08
-
1$\begingroup$ In my HS physics class we had an old CRT monitor that the teacher let us put magnets on. I'm not precisely sure what the lesson was but I have found memories of this. $\endgroup$– zeldredgeCommented Apr 1, 2015 at 14:10
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
8
The paper strips were ironed to make them flat and easy to stick to the CRT screen. Old CRT color screens used (IIRC) around 25kV to accelerate the electrons to excite the phosphors on the screen itself. This resulted in the buildup of a static charge on the inside of the screen, and a corresponding charge on the outer, with the glass acting as a dielectric.
LCDs only use very low voltages, with the exception of the backlight which in older LCD monitors was fluorescent with a power supply voltage of hundreds of volts. Newer monitors use LED backlighting at a few tens of volts maximum. Neither would generate the kind of static fields anywhere near that of CRTs
-
$\begingroup$ But why doesn't it work with my lcd? $\endgroup$ Commented Apr 1, 2015 at 14:17
-
$\begingroup$ Just edited my answer to explain $\endgroup$– user56903Commented Apr 1, 2015 at 14:23
-
1$\begingroup$ Your answer still doesn't explain why I can't find an app that simulates hitting the degauss button. Sigh Oh well $\endgroup$– JimCommented Apr 1, 2015 at 14:33
-
1$\begingroup$ Incidentally - if you take a flat piece of paper and rub it back and forth on your LED screen, it will stick. I just tore a piece off an envelope and did exactly that on my screen: i.imgur.com/JgH3Gua.jpg $\endgroup$– FlorisCommented Apr 1, 2015 at 14:50
-
1$\begingroup$ @Jimnosperm - you're not the first to have this idea: halfbakery.com/idea/LCD_20degauss_20simulator and somebody stepped in to fill the void: candycrushgames.us/apk/… $\endgroup$– FlorisCommented Apr 1, 2015 at 14:53
