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Despite their acronymic similarity, LEDs and LCDs represent

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Despite their acronymic similarity, LEDs and LCDs represent [#permalink] New post 09 Jul 2014, 20:04
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LCD's and LED's
Despite their acronymic similarity, LEDs and LCDs represent distinct display technologies. In LEDs, or light-emitting diodes, two different semiconductor materials are layered together: n-type, in which mobile electrons carry negative charge, and p-type, in which “holes” in an otherwise bound sea of electrons carry positive charge. When electric current flows through the p-n junction between layers, an n-type electron falling into a p-type hole releases a photon, a specifically colored particle of light.

The dominant technology currently used in most consumer product displays is the active matrix liquid crystal diode display (LCD). LCDs apply thin-film transistors (TFTs) of amorphous silicon sandwiched between two glass plates. The TFTs supply voltage to liquid-crystal-filled cells, or pixels, between the sheets of glass. Liquid crystals can twist the polarization, or wave orientation, of light. Just as a guitar string can vibrate sideways or up and down, so a light wave can be polarized horizontally or vertically. Polarizing filters act as selective gates, transmitting light polarized one way but not the other. Within a pixel, liquid crystals in their relaxed, coiled state rotate the polarization of ambient light enough to make surrounding filters transparent. Alternatively, applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque. LCDs that are capable of producing color images, such as in televisions and computers, reproduce colors by blocking out particular color wavelengths from the spectrum of white light until only the desired color remains. The variation of the intensity of light permitted to pass through the matrix of liquid crystals enables LCD displays to present images full of gradations of different colors.

The amount of power required to untwist the crystals to display images is much lower than that required for analogous processes using other technologies, such as plasma. The dense array of crystals displays images from computer sources extremely well, with full color detail, no flicker, and no screen burn-in. Moreover, the number of pixels per square inch on an LCD is typically higher than that for other display technologies; LCD monitors are excellent at displaying large amounts of data with exceptional clarity and precision.
1. According to the passage, the application of an electrical signal or current to both an LED and an LCD pixel results in which of the following?

A. Both the LED and the LCD pixel become bright.
B. The LED becomes dark, but the LCD pixel transmits light
C. The LED becomes bright, but the LCD pixel ceases to transmit light.
D. The LED becomes dark, but the liquid crystals in the pixel uncoil.
E. The LED becomes bright, but the liquid crystals in the pixel coil up.

[Reveal] Spoiler: OA
C



2. The author most likely mentions “plasma” in the third paragraph in order to

A. provide an example of a technology that operates differently than LCDs
B. reinforce the importance of the commercial development of LCDs
C. describe the contrasting workings of another technology
D. indicate the greater number of applications for LCDs
E. explain the features of a competing type of display

[Reveal] Spoiler: OA
A


3. The process through which an LCD monitor displays different colors is most closely analogous to

A. the partial blocking of an hourglass so that a limited stream of grains of sand fall into the lower portion

B. the use of rigid sizing boxes at an airport security checkpoint in order to allow the passage of certain sizes of luggage while excluding other sizes of luggage

C. the soundproofing of a recording studio so that any performances within are muted to those outside

D. the cutting out of characters from a sheet of paper so that a lamp in front of the paper casts shadows in the shapes of the characters

E. the emission of warmer air by an air vent on the outside of a building while an air conditioning system cools the interior of the building

[Reveal] Spoiler: OA
B


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Last edited by carcass on 10 Jul 2014, 10:09, edited 1 time in total.
Edited the title of the passage
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Re: Despite their acronymic similarity, LEDs and LCDs represent [#permalink] New post 10 Jul 2014, 12:42
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Tough one , really.

The first one Alternatively, applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque

The second one The amount of power required to untwist the crystals to display images is much lower than that required for analogous processes using other technologies, such as plasma.

the third one LCDs that are capable of producing color images, such as in televisions and computers, reproduce colors by blocking out particular color wavelengths from the spectrum of white light until only the desired color remains. similar to B

Hope this helps
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Re: Despite their acronymic similarity, LEDs and LCDs represent [#permalink] New post 27 Aug 2014, 07:43
carcass wrote:
Tough one , really.

The first one Alternatively, applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque

The second one The amount of power required to untwist the crystals to display images is much lower than that required for analogous processes using other technologies, such as plasma.

the third one LCDs that are capable of producing color images, such as in televisions and computers, reproduce colors by blocking out particular color wavelengths from the spectrum of white light until only the desired color remains. similar to B

Hope this helps

For me, E makes more sense as an answer to Q2.
Can you explain a little bit?
Re: Despite their acronymic similarity, LEDs and LCDs represent   [#permalink] 27 Aug 2014, 07:43
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Despite their acronymic similarity, LEDs and LCDs represent

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