Q6 - Small experimental vacuum tubes

[Laura Damone]

What does the Question Stem tell us?
"Must also be true" = Inference Question, of the Must Be True variety

Break down the Stimulus:
Whew...this one is a bear. It's conditional and science-y, which can be intimidating for a lot of folks. The key here is not to panic and not to rush. 1st line tells us that some vacuums can take more heat than semiconductors. Next line says that makes them preferable, but only if they were comparable to semiconductors in every other important respect, like max capacity. The last line tells us that the vacuum's max capacity is not currently comparable.

Another option for getting through a stimulus like this is to totally abstract it, stripping away the science-y-ness and leaving only bare bones logic:

A has a quality. Anything with that quality is preferable, but only under condition B. But condition "B" isn't met yet.

Hmm....what does that allow us to infer?

Any prephrase?
Conditional Must Be True questions are prephrasing GOLD. This one tells us vacuums are preferable only if they're comparable in all other aspects, but they're not comparable in max capacity. Using the contrapositive, we can infer that vacuums are therefore not preferable at this time. We have a prephrase!

Correct answer:
A

Answer choice analysis:
A) Correct! A perfect match for our prephrase.

B) No way. We can't predict the future. Plus, comparable max capacity is a necessary condition for their use, not a sufficient one, so we can't say that once we make them comparable anything will be guaranteed.

C) Just because it's a reason doesn't mean it's the only reason. This is a classic Must Be True trap answer, and also, for the record, a classic Necessary Assumption trap answer, since both deal with what must be true, given the truth of the stimulus.

D) Again, we can't predict the future. Maybe vacuums will become comparable in all other respects and be preferable for every application...we just don't know.

E) Like (C), this is that classic trap! Just because it's an advantage doesn't mean it's the only advantage.

Takeaway/Pattern: Conditional Must Be True questions should always be prephrased, even if the subject is intimidating. Slow down when necessary or fully abstract the logic to get rid of the intimidating terminology. Also, don't fall for the classic "A way is the only way" trap!

#officialexplanation

[laurakped]

Explanation check please! Particularly the conditional logic.

Correct answer: (A)

TASK: "Must also be true" = Inference question. NOT in the Assumption Family, don't hunt a conclusion. Attack the stimulus:

- small, experimental vacuum tubes work under heat conditions that are too intense for wimpy semiconductor components
- preferable ---> component with resistance > semiconductors' resistance AND component = semiconductors in all other important ways (ex. max current)
- vacuum tubes have a lower max current than semiconductors

This question rewards understanding the Conditional Logic in the 2nd sentence. "but only if" tells us which way the logic flows and how all these elements relate. "But only if" = THEN / --->. So we can write:

preferable
--->
component with resistance > semiconductors' resistance
AND
component = semiconductors in all other important ways (ex. max current)

How do we know "Preferable" comes BEFORE the arrow and "Components with resistance..." AFTER it? The language tells us. What type of component would be preferable? "Any (component whose resistance to heat is greater than that of semiconductors) WOULD BE (preferable)". The conditions for determining if something is preferable hinge on it being able to take more heat than those feeble semicons can. So it if IS preferable, we know it can NECESSARILY take more heat than semicons. Said another way, it can be preferable ONLY IF it's got a resistance > semicons' resistance. So "preferable" goes in front of the arrow and "resistance > semicons" goes behind it.

And while we can't really predict a right answer, we should note that vacuum tubes DON'T currently meet the Conditional Logic requirements for being preferable to semiconductors: 3rd sentence says they don't have the necessary max capacity.

(A) Aw, snap. Just like we predicted. It's the right answer. To be preferable, you need to be a component with max capacity = semicons' max capacity. VT's don't have that. Since VT's are missing a necessary condition (max capacity), they can't have the sufficient condition (being preferable). (If you thought, "Oh, VT's just trigger one of the sufficient conditions of the contrapositive of the logic we worked out above" nicely done!)

(B) is a prediction about future events. We don't know anything about what will happen once vt's and semicons have comparable max current capacity. Sure, it's possible, but MUST IT BE TRUE? Nope. Eliminate. [NOTE: this is a very common type of wrong answer choice for Inference questions. Many will give you future information that sounds good but actually is unfounded because the stimulus tells us nothing about future conditions.]

(C) The ONLY reason? You sure? What if vt's don't have some of those "other significant" qualities which make something just as good as semicons? It COULD BE TRUE, but need not be true, so eliminate. If you started to doubt this choice the moment you saw "only", good job.

(D) ALWAYS? Really? Eliminate for the same reason as (C). [NOTE: (C) and (D) are yet *another* common wrong answer type for Inference questions: Extreme answers.]

(E) We don't know either way. The passages makes it sound like this could be the only one, but we actually have no idea. Eliminate.

[maryadkins]

How do we know "Preferable" comes BEFORE the arrow and "Components with resistance..." AFTER it? The language tells us. What type of component would be preferable? "Any (component whose resistance to heat is greater than that of semiconductors) WOULD BE (preferable)". The conditions for determining if something is preferable hinge on it being able to take more heat than those feeble semicons can. So it if IS preferable, we know it can NECESSARILY take more heat than semicons. Said another way, it can be preferable ONLY IF it's got a resistance > semicons' resistance. So "preferable" goes in front of the arrow and "resistance > semicons" goes behind it.

This is the one part you're mistaken on in your understanding of the stimulus. "Any X would be preferable" means that if it's X, then it's preferable--not the other way around. Think about it this way. If I say, any dog is preferable to a cat, that means if it's a dog, it's preferable. It doesn't mean that everything preferable is a dog, because "preferable" is very broad in life. If "preferable" had to mean something is a dog, the word couldn't be used in any other context outside of dogs and cats!

What we do have is:

component more resistant to heat than SC --> preferable --> same in all other ways

VT isn't same in all other ways --> isn't preferable