Why does my computer monitor flicker?

Why does a CRT monitor flicker and an LCD moitor doesn't, when a mobile phone, near it, receives a call?

• When we place a mobile phone near a computer monitor, a CRT (cathode ray tube) monitor flickers when the phone rings. But when we place the phone near a LCD monitor, the screen doesn't flicker when the phone rings. Why is this so? Why is the LCD monitor unaffected by the mobile phone's signal interference?

• Answer:

  CRTs have a distinctive funnel shape. At the very back of a monitor is an electron gun. The electron gun fires electrons towards the front through a vacuum which exists in the tube of the monitor. The gun can also be referred to as a cathode - hence the electrons fired forward are called Cathode Rays. At the neck of the funnel-shaped monitor is an anode, which is magnetized according to instructions from the display controller. As electrons pass the anode, they are shunted or pulled in one direction or the other depending on how magnetic the anode is at that time. This moves the electrons towards the correct part of the screen. The electrons pass through a mesh, and this mesh defines the individual pixels and resolution on the screen. Electrons that pass through the mesh then hit the phosphor coating which is on the inside of the glass screen. When the particles hit the phosphor, they immediately light up - causing the light to shine through the front of the monitor, thus making up the picture on the screen. There are three differently colored phosphors for each pixel (known as phosphor triads), and depending on which phosphor the electron hits, that's which color the pixel will light up. This technology can be affected by radio and electromagnetic waves by interfering with the electron's travel path. The anode can not compensate for the outside interference and thus you will see the result on your screen as the electrons arrive at a point other that where they should have. An LCD works by sandwiching a solution of TN liquid crystals between two perpendicularly aligned panes of polarized glass, it becomes possible to manipulate the intensity of light as it passes through this crystalline matrix and out the glass panel at the other end. Depending on the voltage of the electrical charge running through them, liquid crystals will untwist so that the intensity of light able to pass through the second polarized pane is affected. Basically, these displays can switch between light states (where the liquid crystals are fully twisted) and dark states (where the liquid crystals are fully untwisted), or somewhere along the gray scale in between. This is done digitally. Since there are no electrons traveling, but instead a light source that is being blocked and unblocked you won't see any interference since it won't affect the LCDs operation.