电子专业英语lesson17-LCD.ppt

Unit Four Electric appliances How do Liquid Crystal Display TVs work? Have you ever seen a snow crystal? Sometimes its possible to see them for a short moment when snow lands on your hand, but most of the time it melts before you get to see the beautiful hexagon-shaped (six-sided) crystals. Crystals are made up of particles that are arranged in a regular pattern and usually come in solid form. For example, when snow melts, it turns into water and loses its crystal shape. Do you know that there are three states for most objects: solid, liquid and gas? Most things only come in these three forms. However, some material can remain in a state that is somewhat in between a solid and a liquid. In this state, the object is a liquid but still maintains the regular crystal-like arrangement. The existence of this state has been known for a very long time. In fact, there was a research article titled “the flowing crystal” that was published in 1889, over 100 years ago. It took many, many years of research and development to get liquid-crystal display TVs to the point that they are at now. If you put a nail in the middle of two magnets, the edges of the nail will try to point towards each magnet. Similarly, crystals do not have a round shape but have a long narrow shape and when electricity is passed through a crystal, it tries to align itself in the direction of the electrical flow. In a liquid crystal TV, many small compartments are left between two pieces of glass. Each of these compartments holds liquid crystals that are colored red, blue or green. Even if light is shined on the back of the screen, the screen remain black because the liquid crystals are not active and block any light from passing through it. However, when electricity passes through a blue compartment, the liquid crystals in that compartment become active and allow light to pass through. That’s how a screen becomes blue (as shown in Fig.6-1). The way d