Question about RC

This topic has expert replies
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Wed Dec 29, 2010 2:58 pm

Question about RC

by Derek1988 » Mon Feb 14, 2011 11:21 am
Simple question: I am not a native English speaker... (TOEFL 101) and sometimes I do not get the meaning of the CR text. An example from MGMAT CAT 2

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.


As you may grasp, this is a very hart to understand. And I didn't. AndI got 3 wrong answers out of 3.

What can I do when I meet a text and I do not understand it?
Source: — GMAT Strategy |

User avatar
GMAT Instructor
Posts: 1031
Joined: Thu Jul 03, 2008 1:23 pm
Location: Malibu, CA
Thanked: 716 times
Followed by:255 members
GMAT Score:750

by Brian@VeritasPrep » Mon Feb 14, 2011 12:04 pm
Hey Derek,

Great question - and keep in mind that many native English speakers will have trouble reading this much technical jargon, too! That's all part of the GMAT's design. For many RC passages you're not supposed to be able to fully grasp the technical components of the material in a short timespan - what they're testing is whether you can sift through the technical aspects to get a good idea of what the author is trying to say more generally. After all, as a manager of a business, you won't always know what the engineers or R&D scientists are talking about on a technical level, but you will need to be able to interpret that to make decisions.

The best way to attack a technical passage is to look for the words that you do know, and that you know to be important. Those are typically structural terms like "however", "also", "therefore", "despite", etc. These words signal the author's intent, and will appear throughout the multiple RC passages you read so it pays to get to know them. For this passage, I'd focus your attention on:

Despitetheir 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.


Based on emphasizing those few sentences, I think you can get a pretty reasonable understanding of what's going on:

1) Despite the fact that these two technologies are similar, they're also pretty different.
2) LCDs are the dominant current technology, and the second paragraph details how they work
3) The third paragraph shows some advantages of the LCD technology

At this point, without having understood much of the science within, I think you can get a pretty good idea of what the author is trying to do; namely, sell the advantages of LCD technology over that of LED.

More importantly, the key to reading technical passages is to not worry about the details until you have to - at first, just get an idea of what the author is trying to accomplish paragraph-by-paragraph and you'll save time and confidence to attack the questions as they come.[/i]
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep

Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.