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Questions and Answers
What is classical mechanics unable to explain?
What is classical mechanics unable to explain?
- Behavior of subatomic particles (correct)
- Thermodynamics
- Electromagnetic radiation
- Motion of macroscopic objects
The photoelectric effect occurs when the intensity of light exceeds a certain threshold.
The photoelectric effect occurs when the intensity of light exceeds a certain threshold.
False (B)
What happens when the frequency of incident radiation is smaller than the metal's threshold frequency?
What happens when the frequency of incident radiation is smaller than the metal's threshold frequency?
No electron can be emitted.
How does the kinetic energy of the ejected electrons depend on the frequency of light?
How does the kinetic energy of the ejected electrons depend on the frequency of light?
What did Bohr's quantum theory explain?
What did Bohr's quantum theory explain?
What did Compton's study confirm?
What did Compton's study confirm?
A perfect black body reflects all radiation that falls on it.
A perfect black body reflects all radiation that falls on it.
Match the following effects or theories with their descriptions:
Match the following effects or theories with their descriptions:
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Study Notes
Quantum Mechanics' Emergence
- Classical mechanics successfully explains the motion of observable objects.
- It fails to explain the behavior of subatomic particles (electrons, protons, neutrons).
- Quantum mechanics provides a successful explanation for subatomic particle mechanics.
Failures of Classical Mechanics
- Photoelectric Effect: Classical theory predicted no threshold frequency, increasing current with frequency, and electron kinetic energy increasing with intensity. Experiments showed a threshold frequency, instantaneous electron emission regardless of intensity (above threshold), and electron kinetic energy dependent on frequency, not intensity.
- Atomic Stability: Rutherford's classical model predicted atomic collapse due to electron energy loss through radiation. Atoms are stable, contradicting this prediction.
- Compton Effect: Classical physics predicted no wavelength change in scattered X-rays, but experiments showed a wavelength increase, explained by X-ray photons behaving as particles.
- Black Body Radiation: Classical physics failed to accurately predict the observed spectrum of electromagnetic radiation emitted by a black body.
Black Body Radiation
- A black body perfectly absorbs and re-emits all incident radiation, regardless of direction, frequency, or wavelength.
- It's a good emitter, and no perfect black body exists naturally.
- Black body radiation is electromagnetic radiation emitted by heated objects.
- Colder objects emit low-frequency radiation; hotter objects emit higher frequencies.
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