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Despite their acronymic similarity, LEDs and LCDs represent distinct

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Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 28 Aug 2015, 06:18
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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. Which of the following can be inferred about uncoiled liquid crystals in an LCD pixel?

A. Electric currents cause them to release photons.
B. They are in a relaxed state, in comparison to their high-energy coiled state.
C. They are found in one of two wave orientations, horizontal or vertical.
D. They fail to rotate the polarization of surrounding photons enough to allow them to pass through nearby filters.
E. They cause the pixel to become transparent.



2. 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



3.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.




4. The passage indicates that each of the following may be considered an advantage of LCDs relative to other display technologies EXCEPT

A. they consume less power
B. they generally have more pixels per square inch of the display
C. they are able to replicate computer images with little to no loss of detail
D. they reflect a widely adopted standard
E. they represent the latest, most advanced technology



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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 06 Jan 2016, 07:58
Really tough questions! I can't catch the main idea of author. Anyone can give answer and methods to solve it?
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 06 Jan 2016, 23:29
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Here is my take on this question. Feedback as always appreciated.

Para 1: Author starts off by pointing out that the LCD and LED displays are different and goes on to detail the method of working of the LED displays.
Para 2: Author states that the LCD is more popular and then goes on to explain the working of the LCD (very dense in detail)
Para 3: Author continues to give us advantages of the LCD tech and concludes that it is the best display (Almost swears by how good LCD is).

Main Point would something on the lines of: Principles behind 2 distinct displays explained and reasons as to why LCD is superior.

1. Which of the following can be inferred about uncoiled liquid crystals in an LCD pixel?

A.Electric currents cause them to release photons - No mention of photos released in LCD

B. They are in a relaxed state, in comparison to their high-energy coiled state - States the opposite. The passage states - "Within a pixel, liquid crystals in their relaxed, coiled state rotate the polarization of ambient light enough to make surrounding filters transparent" The answer choice incorrectly states that uncoiled state = relaxed.

C. They are found in one of two wave orientations, horizontal or vertical. - The orientation refers to the guitar string used as an example to explain a theory.

D. They fail to rotate the polarization of surrounding photons enough to allow them to pass through nearby filters. - Substantiated by "applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque"

E. They cause the pixel to become transparent. - Opposite again


2. 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 - Passage says that the crystals completely block certain spectra of light.
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 - Correct. The crystals block everything else except the one that needs to be displayed.

C. the soundproofing of a recording studio so that any performances within are muted to those outside - Some spectra do go through at least the ones we see on display!! so no complete "muting" if you'd like.

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 - Found it hard to eliminate this one. My rationale is that this choice doesnt depict the preferential selection as in the case of the crystal.

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 - Not really representative of the preferential selection as in the case of the LCD.


3.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?

Passage states - LED glows when electricity is passed through (Passage excerpt : "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. ")

LCD on the other hand blocks unwanted spectra of light except what is displayed (Passage excerpt: "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)

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.
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 31 Jan 2018, 04:16
Would anyone please explain question 4 ?
Really got a tough time to choose between D and E ...
I could not find in passage 'Widely adopted standard'
But got 'dominant technology' coincides with the option 'most advanced and latest technology '.
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 31 Jan 2018, 04:17
Would anyone please explain question 4 ?
Really got a tough time to choose between D and E ...
I could not find in passage 'Widely adopted standard'
But got 'dominant technology' coincides with the option 'most advanced and latest technology '.
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 31 Jan 2018, 17:15
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soumya170293 wrote:
Would anyone please explain question 4 ?
Really got a tough time to choose between D and E ...
I could not find in passage 'Widely adopted standard'
But got 'dominant technology' coincides with the option 'most advanced and latest technology '.



D can find out from"The dominant technology currently used in most consumer product displays is the active matrix liquid crystal diode display (LCD)."(the second part 's first sentence)
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 15 Jul 2018, 06:23
The author most likely mentions “plasma” in the third paragraph in order to


provide an example of a technology that operates differently than LCDs


reinforce the importance of the commercial development of LCDs


describe the contrasting workings of another technology


indicate the greater number of applications for LCDs


explain the features of a competing type of display
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 23 Jul 2018, 02:11
Tough passage, questions can be answered through careful POE.
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Re: Despite their acronymic similarity, LEDs and LCDs represent distinct  [#permalink]

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New post 23 Jul 2018, 08:38
soumya170293 wrote:
Would anyone please explain question 4 ?
Really got a tough time to choose between D and E ...
I could not find in passage 'Widely adopted standard'
But got 'dominant technology' coincides with the option 'most advanced and latest technology '.



In the beginning of the second paragraph it says that LCD is the most common form of technology.
Re: Despite their acronymic similarity, LEDs and LCDs represent distinct &nbs [#permalink] 23 Jul 2018, 08:38
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