Despite their acronymic similarity, LEDs and LCDs represent distinct

Question

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  
 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.

2  
 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

3  
 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

4  
 4. 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.

5  
 5. In this passage, the author is primarily concerned with

A. delineating the commonalities between two seemingly divergent phenomena
B. contrasting the uses of electrical power for two contrary purposes
C. explicating the scientific underpinnings of two dissimilar technologies
D. describing the economic significance of two processes
E. analyzing the relationship between two methods of displaying information

Manhattan CAT 3

carcass · Answer

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

ronr34 · Answer

For me, E makes more sense as an answer to Q2.
Can you explain a little bit?

CV7585 · Answer

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. T hey 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.

gsrividhya · Answer

Hello,

For second question ? Why not option B..
Just link 2 statements,
The dominant technology... in second paragraph
The amount of power is less..in 3rd para
Link these two it gives more reason for commercial development of LCDs

Experts please advise.

Thank you,
Srividhya

felippemed · Answer

One extra question (750-800, for sure) :!:

OA provided 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. D In this passage, the author is primarily concerned with A. delineating the commonalities between two seemingly divergent phenomena B. contrasting the uses of electrical power for two contrary purposes C. explicating the scientific underpinnings of two dissimilar technologies D. describing the economic significance of two processes E. analyzing the relationship between two methods of displaying information C

felippemed · Answer

If you don't assimilate photon = light, you get all the questions wrong.

The most curious thing is that a photon is not "light" according to the dictionary.com

a quantum of electromagnetic radiation, regarded as a particle with zero rest mass and charge, unit spin, and energy equal to the product of the frequency of the radiation and the Planck constant

I think that Manhattan and GMATClub should retrieve this passage from their databases

only2venkat · Answer

It is true that low power consumption in LCD led to the commercial development. However, I feel that the word plasma is specifically mentioned to give an example by using word such as.. 
Hence A will be most appropriate.

Sent from my vivo V3Max using  GMAT Club Forum mobile app

goforgmat · Answer

The passage as a whole only talks about how LED s and LCD s work. Nowhere you can see the author emphasizing its commercial success. He merely mentions in the second paragraph that LCDs are dominant. Keeping the above points in mind we can safely conclude that option 2 is wrong.

soumya170293 · Answer

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 '.

MinHuiii · Answer

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)

Talayva · Answer

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 A

aragonn · Answer

P1 - LCD n LED defined.
P2 - how LCD works, colours, uses.
p3 - lcd is better then plasma. why how?

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?
Alternatively, applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque
releases a photon, a specifically colored particle of light.

C. The LED becomes bright, but the LCD pixel ceases to transmit light. - no 
------------------------------------

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

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.

A. provide an example of a technology that operates differently than LCDs -

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

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.

PT - Similarity is that something can pass while other can be blocked.
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 -

------------------------------------------------

4. Which of the following can be inferred about uncoiled liquid crystals in an LCD pixel?
P2
Within a pixel, liquid crystals in their relaxed, coiled state rotate the polarization of ambient light enough to make surrounding filters transparent.

The dominant technology currently used in most consumer product displays is the active matrix liquid crystal diode display (LCD).

A. Electric currents cause them to release photons. --- that is in LCD. 
B. They are in a relaxed state, in comparison to their high-energy coiled state. ---- comparision part is not correct.
C. They are found in one of two wave orientations, horizontal or vertical. --- no >>>>>>>>>so a light wave can be polarized horizontally or vertically. 
D. They fail to rotate the polarization of surrounding photons enough to allow them to pass through nearby filters. --- others can be elliminated easily . 
E. They cause the pixel to become transparent. - no >>>> make surrounding filters transparent
--------------------------------------------------

5.In this passage, the author is primarily concerned with

A. delineating the commonalities between two seemingly divergent phenomena
B. contrasting the uses of electrical power for two contrary purposes
C. explicating the scientific underpinnings of two dissimilar technologies - clearly best of the lot.
D. describing the economic significance of two processes
E. analyzing the relationship between two methods of displaying information

aragonn · Answer

u1983

Following lines are used for Q3:

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.

you have to think about a choice which is similar to the given system. let me tell you this in simple terms. hope you know light has 7 colours. the text says that when light pass through matrix it send out 1 colour while absorbs the rest. so one can see that colour only.

on similar pattern find a system which can filter something while let go other. Only B does . Big boxes will be stopped. small will be passed.

In other options everything will pass. Hope it is helpful.

u1983 · Answer

aragonn  ...... Thanks a bunch .

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?
Alternatively, applied electrical signals uncoil the crystals, causing the filters to block light and the pixel to become opaque
releases a photon, a specifically colored particle of light.

C. The LED becomes bright, but the LCD pixel ceases to transmit light. - no

I completely agree that 'uncoil' is a definite clue. But just for my curiosity , could u pls direct me to the part from where I can infer the first part of option C :   |The LED becomes bright|

aragonn · Answer

We know that P1 is for LED P2 is for LCD. Lets focus on this part "The LED becomes bright". Following lines prove that. more over its full form is "light-emitting diodes".

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.

u1983 · Answer

Please excuse me if I am bothering you too much......... But again that is my point.

When applied electricity LED becomes bright ( as it releases photon). 
But in the  OA i.e.,D ................ the 1st part is mentioned as  'The LED becomes dark,'   ........... This is the point of my confusion.

saurabh9gupta · Answer

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

For this question, I picked C but then I realized I made a blunder.

The author just mentioned about plasma ( like an example) but did not describe it.

Just a doubt

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.

The BOLD and Underlined portion explains about the LCDs right and not Plasma?  daagh   GMATNinja   bb

dave13 · Answer

u1983 
 Answer to question # 1 lies in the sentences below:

LCD technology:  Within a pixel, liquid crystals in their relaxed, coiled state rotate the polarization of  ambient light enough to make surrounding filters  transparent.

LED technology:  Alternatively, applied electrical signals uncoil the crystals,  causing the filters to block light and the pixel to  become opaque. i.e not transperent

Answer to Question #3 is in the sentence below

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.

So analogy is following

So LCDs can be programmed so, that they can scan only  certain colors , just like 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

Adambhau · Answer

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

This question asks about a specific detail in the passage: the author’s use of the term “plasma.” This term appears in the first sentence of the third paragraph: “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 correct answer choice will reflect the author’s use of the term “plasma” in this sentence.

(A) CORRECT. The use of the phrase “such as plasma” indicates that the author is providing an example. The example provided represents a technology that utilizes different processes to display images than LCDs.

(B) The use of the term “plasma” does not serve to reinforce the significance of the commercial development of LCDs. The passage gives no other information about plasma, and no information is given about the commercial development of either.

(C) The passage does not describe the workings of how plasma technology displays images.

(D) The use of the term plasma does not serve to reinforce the greater number of applications for LCDs. The passage provides no other information about the number of applications for plasma technology.

(E) The passage does not explain the features of plasma displays.

Despite their acronymic similarity, LEDs and LCDs represent distinct

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GMAT Reading Comprehension (RC) Questions

Despite their acronymic similarity, LEDs and LCDs represent distinct

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