#24 - Concept Reference, Must Be True

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=10866)

The correct answer choice is (D)

The atomic structure of glass is discussed in each of the first three paragraphs. In the first paragraph, the author mentions glass’ lack of a fixed atomic crystalline structure. The next paragraph observes that certain solids, including glass, can indeed flow (though very slightly and very slowly). In the third paragraph, the author adds that in order to increase the speed of glass’ flow, the glass would need to be brought to a temperature of 350 degrees Celsius or higher.

Answer choice (A): This is an Opposite Answer, since glass behaves as a solid, even though it has certain properties of liquids (lines 10-19).

Answer choice (B): Glass would take much longer than a few millennia to sag noticeably, so this choice fails the Fact Test and cannot be the right answer to this Must Be True question (lines 25-30).

Answer choice (C): Since glass can flow more quickly when brought to its transition temperature (lines 39-43), this is an Opposite Answer and should be eliminated from contention.

Answer choice (D): This is the correct answer choice. As prephrased above, the author observes that glass can flow downward under its own weight if it is heated to its glass transition temperature (lines 39-43).

Answer choice (E): At the end of the first paragraph, the author mentions that the atoms in glass are not arranged in a fixed crystalline structure, even when the glass is cooled below its transition temperature.

[Haleyeastham]

Can you please explain how answer choice D is suggested by the passage?

Thanks!

[David Boyle]

Can you please explain how answer choice D is suggested by the passage?

Thanks!

Hello Haleyeastham,

Answer D, "flow downward under its own weight if it is heated to its glass transition temperature", is suggested by "Glass does not have a precise freezing point; rather, it has what is known as a glass transition temperature, typically a range of a few hundred degrees Celsius. Cooled below the lower end of this range, molten glass retains an amorphous atomic structure, but it takes on the physical properties of a solid." plus "Under the force of gravity, certain solid materials including glass can, in fact, flow slightly." plus "the fact that for glass to have more than a negligible ability to flow, it would have to be heated to at least 350 degrees Celsius."

Hope this helps,
David

[mo_wan]

Is b) wrong because it implies that it always acts as a liquid? But it only acts as a liquid when it reaches the temperature transition?

C) is wrong because when it reaches it's transition it acts as a liquid with solid properties?

Not sure why D is right. I know it said that gravity allows for flow but didn't mention anything about glass transition temp.


The last part of para 1 was super confusing for me.

[mo_wan]

Is b) wrong because it implies that it always acts as a liquid? But it only acts as a liquid when it reaches the temperature transition?

C) is wrong because when it reaches it's transition it acts as a liquid with solid properties?

Not sure why D is right. I know it said that gravity allows for flow but didn't mention anything about glass transition temp.


The last part of para 1 was super confusing for me.

[Adam Tyson]

B is incorrect because it is an opposite answer, mo_wan, in that the author is telling us that this belief about glass flowing downward over time is false. It wouldn't take a few millennia - it would take something more than the age of the universe, according to the text.

C is wrong for exactly the reason you stated. Well don!

D is right because that is exactly what the passage told us. See lines 14-19 and then again at lines 39-44. Glass will flow like a liquid if it is heated to its transition temperature, below which it acts as a solid.

This passage is all about the persistent belief that glass flows like a liquid, slowly over time, and showing through studies that the belief is wrong. Glass flows only when heated a lot, and old windows are thicker at the bottom not because the glass has flowed downward but because of the way window glass used to be made.

[jwheeler]

Between lines 13-19 and 39-43, it doesn't necessarily state that the 350 is the glass transition temperature. It says it's typically in the range of a few hundred degrees C, but doesn't ever explicitly equate that and the 350. I had a hard time seeing the justification of D because of that.

[Robert Carroll]

j,

The exact point of the glass transition temperature is irrelevant for this question. The properties of glass above that temperature are all that you need to know to prove answer choice (D) correct. Is it possible you were thinking of another question?

Robert Carroll

[demk26]

Hi all,

Can someone please explain why answer choice (A) is wrong? It states that "it retains an amorphous atomic structure, but takes on the physical properties of a solid."

Does that mean that it behaves like a liquid, but has the physical properties of a solid, or vice versa?

Also, how do we assume that the glass transition temperature and the 350 degrees mentioned in the passage or talking about the same thing, which would make answer choice (D) correct?

Thank you!

[KelseyWoods]

Hi demk26!

The statement "molten glass retains an amorphous atomic structure, but takes on the physical properties of a solid" describes glass as behaving like a solid (takes on the physical properties of a solid) even though it has certain properties of liquids (amorphous atomic structure). Further up in that first paragraph is also helpful: "the atoms in glass are not arranged in a fixed crystal structure. In this respect, the structure of liquid glass and the structure of solid glass are very similar." So glass behaves as a solid, but it has an atomic structure that is similar to a liquid.

The first paragraph also provides us with some information to help with the transition temperature of glass: "a glass transition temperature, typically a range of a few hundred degrees Celsius." This discussion of the glass transition temperature helps us understand that the 350 degrees Celsius mentioned later is a reference to the point at which glass transitions between its liquid and solid states.

Hope this helps!

Best,
Kelsey