PrepTest 115

[lcid:3558] Prep Test 115 LSAT — Reading Comp — S3 Reading comp

Passage

Questions 17-23  .        With the approach of the twentieth century, the  . classical wave theory of radiation—a widely accepted Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • Background info on old theory (classical wave theory) and its fundamental assumption (energies continuously increase as wavelength decreases)
  • Views, minor Meta-Structures, and the author's attitude
    • The classical wave theory (old theory):
      • All forms of electromagnetic radiation exist in waves (second sentence)
      • Assumes that as wavelength decreases, the energy increases smoothly and continuously (last sentence)
    • Examples of electromagnetic radiation:
      • Gamma rays, X rays, radio waves, heat, and light (first sentence)
    • Comparison of radiation to volume dial, according to wave theory:
      • Both increase smoothly and continuously (last sentence)
    • Author's attitude: "encounter obstacles" (first sentence); "fundamental assumption" (last sentence)

Paragraph 2

  • Paragraph note
    • Evidence challenging the assumption ("blackbody" objects do not radiate the predicted energy at short wavelengths)
  • Views, minor Meta-Structures, and the author's attitude
    • Definition of "thermal" or "blackbody" radiation:
      • Radiation from an object due to the object's temperature (first sentence)
    • Definition of "ultraviolet catastrophe":
      • Result of advanced experiments that found that blackbody objects did not radiate any energy at short wavelengths (when classical wave theory would suggest that they would radiate a lot of energy at this wavelength)
    • Examples of materials that might be used in blackbody experiments:
      • Black velvet or soot (first sentence)
    • Author's attitude: "major challenge" (first sentence); "in fact" (last sentence)

Paragraph 3

  • Paragraph note
    • A new hypothesis to account for evidence (Planck's "levels" of energy, which lacked an explanation)
  • Views, minor Meta-Structures, and the author's attitude
    • Planck's hypothesis:
      • Energy increases incrementally, not smoothly, as wavelength decreases (second sentence)
    • Comparison of radiation to a volume dial that clicks, according to Planck's hypothesis:
      • Both can only be set to certain levels (second sentence)
    • Physics community's view:
      • Dubious because Planck didn't yet have a physical explanation (last sentence)
    • Author's attitude: "important contributions" (first sentence), "bizarre" (second sentence), "perfectly fit" (second sentence)

Paragraph 4

  • Paragraph note
    • An explanation for Planck's hypothesis (Einstein discovers photons, which are only emitted in certain units and increase at specific wavelengths)
  • Views, minor Meta-Structures, and the author's attitude
    • Einstein's theory:
      • Radiation is actually particles called photons, which are only emitted in certain amounts and only increase at specific wavelengths (fourth sentence)
    • Author's attitude: "theoretical justification" (first sentence); "confirm" (fourth sentence); "new vision" (last sentence), "still in place today" (last sentence)

Main Point: Planck's theory of radiation corrected one of classical wave theory's assumptions, which was later confirmed when Einstein and other physicists provided theoretical and experimental confirmation of Planck's theory.

Meta-Structure?

Old Approach/New Approach: This follows an Old Approach/New Approach (perhaps more accurately modified to "Old Theory/New Theory) Meta-Structure, although several other Meta-Structures could apply to this passage.*

As is the case with most passages that follow this Meta-Structure, the first part of the passage introduces the old theory. In this case, the old theory is the classical wave theory of radiation, which held that the energy radiated off an object increases as the wavelength decreases. This passage also includes two common features of Old Approach/New Approach Meta-Structures: evidence that doesn't fit the old theory and a controversial new theory. In this passage, those are the blackbody radiation experiments (from the second paragraph) and Planck's theory (from the third and fourth paragraphs). Planck posited that the energy radiated off an object increases in intervals, not smoothly, as the wavelength decreases.

When the passage utilizes an Old Approach/New Approach Meta-Structure, the main point is the author's opinion of the new approach. In this passage, we can infer from the strong, supportive tonal phrases like "perfectly fit" (P3, S2), "theoretical justification" (P4, S1), and "confirm" (P4, S4) that the author buys Planck's theory. The author accepts Planck's theory because Einstein and other physicists were able to provide theoretical and experimental confirmation of this theory. Therefore, the main point should reference these other physicists. The author never summarizes their opinion of Planck's theory in one or two sentences, so we summarized their position for them: "Planck's theory of radiation corrected one of classical wave theory's assumptions, which was later confirmed when Einstein and other physicists provided theoretical and experimental confirmation of Planck's theory."

*One could justifiably say that this passage utilizes a Phenomenon/Explanation Meta-Structure (since Planck's theory explains blackbody radiation), a Problem/Solution or Correcting the Record Meta-Structure (since Planck's theory fixes a problem classical wave theory had when accounting for blackbody radiation), or even an Innovative Subject Meta-Structure (since Planck's theory was an innovative and controversial deviation from the then-accepted theory). Any of these Meta-Structures would help you identify the passage's main point and organization.

Last Thoughts?

Let's pay close attention to the analogies to volume dials the author makes in the first and third paragraphs. The test-makers assume you probably don't know much about science. So, they'll often provide analogies to everyday ideas or objects to help you out. These analogies will relate a scientific concept to something you already understand.

When you encounter these analogies, use them to help you understand what the passage is talking about. These analogies clarify the central subject matter or supporting evidence by relating the arcane subject matter to something we can all picture. Take a moment if you don't even understand how the analogy relates to the subject matter. Re-read that paragraph if necessary, and don't proceed without figuring out how the analogy relates to the passage's subject matter. These analogies are carefully placed — if we don't understand the analogy, we will have a hard time understanding anything that follows.

In this passage, the radio dial analogies show us the key difference between the classical wave theory and Planck's hypothesis. The classical theory argues that energy increases smoothly and continuously, like a volume dial that increases any time you twist it clockwise. By contrast, Planck's hypothesis proposes that energy increases at intervals, like a volume dial that only increases when you click the dial to a higher preset level.

Question prompt

Which one of the Remaining source text redacted.
Why the credited answer is right

Credited answer: A

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

Question Type

Science

Strategy Overview

Refer to notes or what you highlighted/underline to locate where the passage discusses blackbody radiation, and refer to the relevant part of the passage as needed to find that answer choice that must be true

Answer Anticipation

For questions that ask us to infer, from a few details in the passage, an answer choice that must be true, quickly finding and reviewing those details is critical. That is why we make brief notes describing the role of each paragraph and highlight or underline definitions and the minor Meta-Structures — doing so helps us find the salient information efficiently and reliably. Once we review that part of the passage, we can look through the answer choices to see which one is best supported by what we reviewed. Since the question stem asks us to make an inference, the correct answer probably won't restate something from the passage. Instead, the question will likely require us to draw a connection between a few different pieces of information.Here, the question asks about blackbody objects in the second paragraph. If necessary, we can review the blackbody experiments described in that paragraph. Experimenters used objects like black velvet or soot to measure "thermal radiation" — dubbed "blackbody" radiation due to the objects used in the experiments (P2, S1). They used these "blackbody" objects because the objects don't reflect other radiations, allowing the physicists to be confident that they were measuring the thermal radiation emitted by the objects (P2, S2). But their experiments found that blackbody objects did not radiate any energy at short wavelengths, when classical wave theory would suggest that they would radiate a lot of energy at this wavelength (P2, S3-S4). These adorable little drama queens called this discrepancy the "ultraviolet catastrophe" (P2, S4).It's very difficult to anticipate exactly what the correct answer will say, but our review of these experiments will help us analyze each answer choice. Let's ask ourselves whether we can infer each answer choice from the facts we just recapped.

Answer choices

  1. A
    Radiation reflected by and Remaining source text redacted.
    Why choice A matches the stem

    (A) Can we infer this from the facts we reviewed in the second paragraph?

    Why, yes! Remember why these physicists had to resort to objects like black velvet or soot. They used these "blackbody" objects because the objects don't reflect other radiations, allowing the physicists to be confident that they were measuring the thermal radiation emitted by the objects. If the physicists could readily distinguish the radiation reflected by an object and the radiation emitted by an object, they wouldn't have to use a non-reflective object like soot (which, it must be said, poses a high risk of staining the physicists' white lab coats). Since the physicists resorted to using non-reflective blackbody objects, it must be true that it's difficult to distinguish the radiation reflected by an object and the radiation emitted by an object. Therefore, (A) can be inferred from the facts we reviewed.

    That said, (A) is not stated explicitly in the passage. We didn't anticipate that the correct answer would say this, either. So, only the most confident test-takers would select (A) without reading the remaining answer choices. For the rest of us, we can select (A) after we eliminate the remaining choices.

  2. B
    Any object in a Remaining source text redacted.
    Why choice B is not credited

    (B) Can we infer this from the facts we reviewed in the second paragraph?

    No. We're told that "blackbody" objects have little or no reflective capability" (P2, S1). They're not "blackbody" objects because they appear dark to us. Even in a dark room, some objects could be highly reflective.

    Plus, this answer choice uses bold, SCOTUS-y language that is universal ("any") and superlative ("ideal"). This language is hard to support, so the correct answer to a Must Be True question probably won't feature such words. Therefore, we can confidently eliminate (B).

  3. C
    All blackbody objects of Remaining source text redacted.
    Why choice C is not credited

    (C) Can we infer this from the facts we reviewed in the second paragraph?

    Nope. In fact, this contradicts what we reviewed. We're told that experimenters used blackbody to measure "thermal radiation" — how the wavelengths change at different temperatures (P2, S1). If blackbody objects emitted the same wavelengths regardless of temperature, they wouldn't help researchers measure how wavelengths change at different temperatures!

  4. D
    Any blackbody object whose Remaining source text redacted.
    Why choice D is not credited

    (D) Can we infer this from the facts we reviewed in the second paragraph?

    Not quite. These physicists indeed used blackbody objects to measure "thermal radiation" (P2, S1). So, if these physicists couldn't manipulate these objects' temperatures, the objects wouldn't be of much use in their experiments.

    But note the bold, SCOTUS-y language in this answer choice. It expresses a high degree of universality ("little use in an experiment"). That suggests these blackbody objects wouldn't be useful in any experiment. That statement is hard to support. Indeed, even if these blackbody objects wouldn't be useful in experiments measuring thermal radiation, perhaps they could be of use in other experiments. So, we can cross off (D).

  5. E
    Thermal radiation cannot originate Remaining source text redacted.
    Why choice E is not credited

    (E) Can we infer this from the facts we reviewed in the second paragraph?

    Nope. In fact, this contradicts what we reviewed. We're told that experimenters used blackbody to measure "thermal radiation" — how the wavelengths change at different temperatures (P2, S1). If blackbody objects did not emit thermal radiation, they'd be totally useless in these experiments. We can cross off (E).

What this tests

Discussion

View all discussions Start a discussion