Self-paced
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
22.
The primary function of the █████ ███ ██████████ ██ ███ ███████ ██ ██
a
describe the process ██ █████ ███ ████████ ██████████ ███ ██████████ ██ █ █████████ ██████
Although P2 shows how evidence is inconsistent with wave theory’s assumption, it doesn’t show how a competing theory undermines wave theory’s assumption. Later in the passage we get Planck’s hypothesis, which might be characterized as a competing theory, but this doesn’t imply that the competing theory did any dismantling or that the author’s purpose in P2, before the competing theory is mentioned, is to describe how a competing theory dismantled wave theory’s assumption.
b
introduce a central ██████████ ██ █ ██████████ ██████ ███ ███ ████████████ ████████ ████ ███ ██ ███ ████████████ ██ ████ ██████
This best captures the purpose of P1 and P2 as explained below the question stem. P1 introduces a “fundamental assumption” of wave theory and P2 describes evidence that eventually led to the discarding of wave theory.
c
explain two competing ████████ ████ ███ █████ ██ ███ ████ ████████████ ████████
We don’t get a description of competing theories in P1 or P2.
d
describe the process ██ █████████ █ ██████ ██ █████ ██ █████████ ████████████ ███████
We don’t get any description of retesting of wave theory in P1 or P2. P2 doesn’t describe any additional experiments beyond those that produced evidence inconsistent with wave theory. In addition, there’s no indication that the experiments that produced evidence inconsistent with wave theory were intended to “retest” wave theory.
e
provide the basis ███ ██ ████████ ████████ ██ ███████ █ ███ ██████
The author doesn’t make an argument intended to dismiss any “new theory.” Rather, the passage describes how Planck’s hypothesis overturned wave theory. Planck’s hypothesis is the new theory — the author never argues that it should be dismissed.