PT115.S3.P3.Q21 > Analytics

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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?"

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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.

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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.

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

21.

The passage provides information that ███████ ████ ██ ███ █████████ █████████ ███████

What did Planck's ██████████ █████ ██████ █████████ ███ ██ ███████ ████

Answered.

What led to ███ ██████████ ███████████ ██████████ ██ ████████ ██████

Answered. The community initially was critical of Planck’s hypothesis, in part because he didn’t present a physical explanation. Other physicists eventually provided a physical explanation.

Roughly when did ███ █████████ █████████ ███████████ ████ ██████

Answered. The experiments occurred “near the turn of the century,” which refers to the beginning of the 20th century.

36%

What contributions did ██████ ████ ██ █████████ ████ ███████

Not answered. Although we know that Planck showed that one of the assumptions underlying classical wave theory is wrong, that’s not a contribution to classical wave theory. In fact, Planck’s hypothesis “directly opposed” classical wave theory.

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Answered.

18%

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