【People's Education Press】High School Physics Elective Compulsory Course III: Blackbody Radiation and Planck's Quantum Hypothesis

Research on blackbody radiation revealed the fundamental shortcomings of classical physics in explaining microscopic thermal radiation. To eliminate the so-calledultraviolet catastrophe, Planck broke with the traditional notion of continuous energy change and creatively proposed the 'quantum' hypothesis, marking a revolutionary leap that heralded the birth of quantum physics.

Core Physical Laws

Ideal Blackbody: An idealized physical model that completely absorbs electromagnetic waves of any wavelength without reflection.
Planck's Quantum Hypothesis: Energy exchange is discontinuous, with the smallest unit being a quantum $\epsilon = h u$.
Planck's Constant: $h = 6.626 \times 10^{-34} \text{ J} \cdot \text{s}$.

💡 Intuitive Analogy: Slide vs. Stairs

Classical physics views energy as continuous, like a slide; Planck argued that microscopic energy behaves like stairs—you can only stand on specific steps. On a macroscopic scale, these tiny steps appear as a smooth slope, but at the atomic level, this discontinuity is fundamental.

QUESTION 1

Which of the following descriptions about a 'blackbody' is correct?

A blackbody must be a black object

A blackbody does not reflect electromagnetic waves but can emit them outward

A blackbody neither reflects nor emits electromagnetic waves

Only high-temperature objects can be considered blackbodies

QUESTION 2

What hypothesis did Planck propose to solve the 'ultraviolet catastrophe'?

The speed of electromagnetic waves varies in vacuum

Blackbody radiation follows Wien's displacement law

Charged particles radiate or absorb energy discontinuously, in the form of quanta

Light is fundamentally a mechanical longitudinal wave

QUESTION 3

Given the visible light wavelength range is approximately $400 \sim 760 \text{ nm}$, what is the approximate energy quantum corresponding to $400 \text{ nm}$ light?

$4.97 \times 10^{-19} \text{ J}$

$2.62 \times 10^{-19} \text{ J}$

$6.63 \times 10^{-34} \text{ J}$

$3.00 \times 10^{8} \text{ J}$

QUESTION 4

Why do we perceive the energy of a macroscopic spring oscillator as continuously changing when observing its motion?

Macroscopic objects do not follow quantum mechanics

Planck's constant $h$ is extremely small, causing macroscopic energy quanta to be exceedingly fine, appearing pseudo-continuous

Spring oscillators are not charged particles and thus have no energy quanta

QUESTION 5

Which description correctly characterizes the performance of classical physical formulas in blackbody radiation experiments?

The Rayleigh formula agrees with experiments in the long-wavelength region but diverges to infinity in the short-wavelength region

Wien's formula closely matches experiments in the long-wavelength region

Planck's formula applies only to the short-wavelength region