Reading comp PrepTest 140 · Section 4 · Question 26

Passage

Questions 20-27  .       Physicists are often asked why the image of an  . object, such as a chair, appears reversed Remaining source text redacted.
Passage walkthrough
Passage SummaryTopic: Science

Paragraph 1
  • Paragraph note
    • A question/phenomenon is introduced, along with an answer/explanation
  • Views, minor Meta-Structures, and the author's attitude
    • Phenomenon - Mirrors reverse images left-to-right instead of top-to-bottom
    • Explanation - "Field-of-Sight" explanation - the reversal reflects how human field of sight is rotated (vertical axis)
    • Base example - Chair
Paragraph 2
  • Paragraph note
    • Another answer/explanations is presented, and the Author gives an opinion on it
  • Views, minor Meta-Structures, and the author's attitude
    • Explanation 2 - Mirrors reverse front-to-back, which makes sense if you think about the reflected chair as being inside the mirror
    • Problem with Explanation 2 - Most notable: Based on false premise, since the "chair" inside the mirror isn't real
Paragraph 3
  • Paragraph note
    • Why Explanation 2 is appealing
  • Views, minor Meta-Structures, and the author's attitude
    • It makes sense with our senses, since we "see" the chair in the mirror and thus think of it as real
    • Example - We don't focus on mirrors but on objects in them
Paragraph 4
  • Paragraph note
    • Another reason Explanation 2 is appealing, with the Author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Scientists try to explain without referring to observer
    • Author - When you're trying to explain an observation, you need the explanation to include the observer
Main Point:
While the appeal of the "front-to-back" theory of how mirrors work is understandable, it ultimately fails because a correct explanation needs to include both the mirror and the person looking into it.

Key Lines:
Lines 1-4 - The question/phenomenon is brought up
Lines 4-7 - A first explanation is presented
Lines 14-16 - A second explanation is presented
Lines 21-23 - The Author points out a flaw in the second explanation
Lines 26-27 - The Author explores the appeal of the second explanation
Lines 42-44 - The Author explores another reason for the appeal of the second explanation
Lines 48-51 - The Author states her conclusion about what a proper theory of mirrors must do

Meta-Structure:
Phenomenon/Explanation (or Question/Answer, which is very similar) - Here, the phenomenon is the "reversed" image in mirrors, the question, why does that happen? One explanation is that it reverses around the human field-of-sight axis. Another is that it reverses things front-to-back, but the Author says this is "based on a false premise" (Lines 22-23). Finally, the Author concludes that a proper explanation needs to take both the observer and what mirrors do into account.

Last Thoughts:
First, this is a notoriously difficult passage, so if you struggled, you're in good company! When that happens, rely on the structure and statements of opinion. Those two things will help you get through the difficult passages.

The first paragraph is a little confusing, so we should expect some questions on that—we'll need to head back to figure out what the correct answer is for any questions dealing with the concept of field of sight axes and rotation.

One thing that's absolutely important to think about—the Author's closing statement, where we finally learn her opinion on the subject of explaining mirrors. While two theories are presented, the Author concludes not with the acceptance of one theory over the other, but rather with the adoption of a criterion by which theories should be judged. She concludes that a theory is valid "only if we consider both what mirrors do and what happens when we look into mirrors" (Lines 49-51).

How does this apply to the two theories? We know that she pointed out an appeal of the second theory (the Reverse Image theory) is that it cuts out the observer, so she believes that theory isn't a good one (which lines up with her stating it relies on a false premise). The first theory does rely on the observer to explain how a mirror works—it relies on human vision featuring a vertical axis, explaining the left-to-right reversal. But just because it matches up with a requirement for a valid theory doesn't mean the Author accepts it—she never explicitly does, so we have to be careful about selecting answers that are too accepting of that theory.

Question prompt

The author would be Remaining source text redacted.
Why the credited answer is right

Credited answer: B

The notes below walk through why it fits the stem and how to eliminate the rest.

Question Type

Science

Answer choices

  1. A
    This explanation is based Remaining source text redacted.
    Why choice A is not credited
    Incorrect. (Line 4; Lines 44-45) The Author does note that the field-of-sight explanation is "simply" that an image is reversed in a certain way. However, the traditional desire of physicists mentioned in Paragraph 4 is to remove the observer from the equation, which the field-of-sight explanation doesn't do in focusing the explanation on the viewer's vision.
  2. B
    This explanation does not Remaining source text redacted.
    Why choice B matches the stem
    Correct. Question Type:
    Must Be True

    Strategy Overview:
    Review the Author's statements of opinion on the explanation in question

    Answer Anticipation/Relevant Lines:
    Finally, a question about the field-of-sight explanation! This was mentioned in the first paragraph, so we should head back there.

    In looking at that paragraph, however, there's no statements of opinion, so the correct answer could bring up these individual details. After all, the Author is the one who wrote those details out, so she'd agree with them.

    However, we can also consider if any of her opinion statements reflect on this explanation. And while most of her opinion statements were about the front-to-back explanation, one at the end wasn't—a proper explanation for how mirrors work must include both the mirror and the observer. The field-of-sight explanation, in relying on human field of sight, does just that. So one potential answer is that the field-of-sight theory meets one criterion for a proper explanation of how mirrors work.

    Let's stay flexible as we work through the answers while keeping this one in mind.

    Answer Explanation:
    (Lines 21-25) This is a tricky correct answer. The Author says that the "most notable" detail of the front-to-back explanation is that it treats the object in the mirror as if it were a three-dimensional object. If that were true of other explanations, then it wouldn't be the "most notable" thing about it. Therefore, the field-of-sight explanation can't also treat the object in the mirror as a 3D object, so this is the correct answer. Note that this would be very easy to miss if you didn't focus on a common important element in RC passages—superlatives ("most notable").

    Key Takeaway:
    Always note superlatives in the passage! They will show up, either as the basis for a question or in an answer choice. Here, knowing that something was the "most notable" feature of one explanation let us infer that it couldn't also feature in another.
  3. C
    This explanation fails to Remaining source text redacted.
    Why choice C is not credited
    Incorrect. (Lines 6-12) The entire field-of-sight explanation talks about the viewer, so this answer couldn't be more wrong.
  4. D
    This explanation assumes that Remaining source text redacted.
    Why choice D is not credited
    Incorrect. (Line 34) The closest that the passage gets to saying this is when it notes that mirrors are "an exception" to the equation between our mental constructs and our primary sense perceptions. However, that's because we "see" a 3D object when it's really a 2D object. But that falls short of saying that people aren't aware of this discrepancy—we might know that the chair is a 2D image, but we treat it as a 3D image because that works and gives us more information.
  5. E
    This explanation is unsuccessful Remaining source text redacted.
    Why choice E is not credited
    Incorrect. (Lines 48-51) First, the Author never explicitly states that the field-of-sight explanation fails. Just because she moves on to another explanation doesn't mean she dismissed the first one, especially since she does dismiss that second one. Second, the only criterion raised by the Author is that a proper explanation has to take both the mirror and the observer into account, and this one does.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 13%
  2. B Credited 58%
  3. C 17%
  4. D 6%
  5. E 5%

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