Reading comp PrepTest 115 · Section 3 · Question 23

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.

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.

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.