Why is PC screen not stable?

[aashima]

I have noticed this many a times and the very thought has always been pestering me. Whenever, while watching some movie or documentary, if they include a computer screen in it, the screen is not stable and is full of horizontal vibrations. Same thing is experienced if we try to capture a photogragh of the computer screen from a camera or mobile phone.
Can anybody help out with the reason?

[raj87verma88]

Yes, I have seen the same and always thought that it must be a very old computer that they were using. Will search the answer and reply here.

[friendster7]

Your cell phone emits a strong electromagnetic (radio) field. That can then interfere with the electronics in the monitor.

Typically a cell phone when it is not in use sends little 'chirps' out so it can talk to the cell towers around it, lets them know where it is in case somebody wants to call you, update the time, whatever else.

When you talk it links to the nearest free tower and radiates continuously. That is why you have so much more standby time compared to the talk time.

With the phone next to the computer the signal from the chirps are strong enough to induce significant voltages in the electronics of the monitor and the speakers, so you get a flicker and a click from the speakers.

It is probably a good idea to move your cell phone further away. The signal drops off quickly so you should not have to move it very far.

[raj87verma88]

but what about the case of movies. Suppose you are watching news and they show some computer project somewhere in a village, you will notice that the screens of the computers will not be stable, a horizontal white line starting from the bottom of the screen will travel towards the top, its as if there is a wheel behind that is rotating the screen, and it keeps on repeating. Nothing like the disturbances you get when a mobile is placed next to a screen.

[ash]

Aww you guys, its nothing really. You are just watching the monitors screen refresh rate in action!

I guess its cause the camera refresh rate is similar to the monitors one.

[anupam011]

yes dear its the refresing rate and capturing rate diffrences in monitor and video cam respectively that causes that.....

[MaRo]

Okay it doesn't happen when I capture video for LCD screen

[anupam011]

yes because LCD doesnt have refreshing rate phenomena.
(LCD displays use two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light.)
so there is only ON and OFF Function of crystals.and LCD do not have a CRT tube whose beam refreshin we was talkin about

[gohm]

Everyone is right, due to refresh rates & getting out of sych between the multiple crt devices with multiple scan rates(all these devices scan their image in lines) from the monitor/TV, TV camera and then monitor/TV again. The blank portion appears as lines to our eye as the normal picture refresh rate is fast enough for our brain to transpose into movement. The faster the refresh rate, the less line effect you will have. What a great question!