Self-study
P1
With the approach of the twentieth century, the classical wave theory of radiation—a widely accepted theory in physics—began to encounter obstacles. ████ ██████ ████ ████ ███ ███████████████ ███████████████ ██████ ████████ ████ █████ ███ █ ████ ██ █████ ████████████ █████████ ████ ███ ██████████████ ██ ███ ████ ██ ██████ ███
Challenge to Existing Theory ·
Classical wave theory claims that all radiation exists as waves
If this theory is being challenged, that must mean that some (or all?) radiation doesn't take the form of waves?
Theory's Assumption ·
Wavelength and energy are continuous
Continuous means that any conceivable energy value could occur in nature. But if that's the assumption, then it probably will turn out to be false. So... what's the opposing concept to "continuous?"
P2
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Phenomenon (Unexplained by Wave Theory) ·
"Blackbody" radiation
"Blackbody" radiation is the heat(?) emitted by an object. The object is black so that it doesn't reflect other forms of radiation (e.g., light in the visible wavelengths). That way, physicists can be sure that they're measuring radiation emitted by the object, as opposed to radiation that merely bounced off that object.
Wave Theory's Prediction ·
Blackbody objects would radiate more at short (compared to long) wavelengths
Prediction False ·
Physicists found almost no short wavelength radiation
The theory predicted that they would find a lot of short wavelength radiation, e.g., ultraviolet radiation. But experimental results contradicted that prediction.
P3
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New Hypothesis ·
Planck theorized that energy was discrete
Planck discarded wave theory's energy continuum (like a smooth turning dial). He didn't think that energy could take on any value. He hypothesized that energy could only take on discrete values. So to move from one energy level to the next involves a jump (like a dial that clicked into place).
Reception of Hypothesis ·
Physics community initially skeptical
Because Planck didn't provide a mechanism to explain how discrete energy jumps occurred.
P4
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Support for Hypothesis ·
Einstein (and others) provided theoretical justification
Found that energy values were discontinuous and found threshold beyond which no energy is emitted.
New Theory ·
Einstein theorized that radiation is composed of particles called photons
Photons can be emitted only in discrete units and at certain wavelengths, corroborating Planck's hypothesis.
Passage Style
Phenomenon-hypothesis (RC)
Single position
23.
The passage is primarily concerned ████
a
discussing the value ██ ███████████ ██ █ ██████████ ██████████
The author doesn’t try to draw lessons about the value of speculation. Although that’s a lesson we might draw as a reader based on the events described in the passage, there’s no evidence that this is what the author intends by writing the passage.
b
summarizing the reasons ███ ███ █████████ ██ ██ ███████████ ██████ ██ ███ ██████████ █████████
The author does a lot more than describe why wave theory was overturned. She focuses on the development and later acceptance of Planck’s hypothesis; (B) doesn’t capture this purpose. In addition, the author doesn’t “summarize” the reasons wave theory was overturned; we don’t get a list of reasons.
c
describing the role ████ ████████████ ████████ █████ ██ █ ██████████ ██████████
Although we as readers might make inferences about the role of experimental research in physics, there’s no evidence the author’s primary purpose is about the role of experimental research. The author focuses instead on telling us about the development of one scientist’s hypothesis and its later acceptance.
d
examining a critical █████ ██ ███ █████████ ██ ████████ ██████████ ███ ██████ ██ █ ████████ ██████████
This is the best answer. The author focuses on an important stage in the evolution of theories concerning the nature of radiation. That stage is the period during which experimental evidence was inconsistent with wave theory, and a scientist proposed a new theory that would soon be accepted.
e
comparing the various ███████████ ████ ███ ██ ███ ██████████ ██ █ ██████████ ██████████
Although the passage does identify a fundamental assumption of wave theory, the author never compares this assumption to other assumptions. Also, (E) doesn’t capture the author’s focus on the development and acceptance of Planck’s hypothesis.