Prelude to Quantum Theory

The development of quantum theory was driven by several experiments, each involving the interaction of light and matter. To explain the results obtained in these experiments, scientists had to reformulate the physical laws that govern the behavior of particles at the atomic scale. In this section, we focus on a few of these experiments and discuss how they contributed to the development of important new ideas and undoubtedly the biggest scientific revolution of the past 100 years. 

Planck s postulate can be rephrased in this more general way The energy of a quantum of electromagnetic radiation is proportional to the frequency of the radiation— the higher the frequency, the greater the energy. This is summarized by what we now call Planck s equation. 

A FIGURE 8-8 Spectrum of radiation given off by a heated body 

A red-hot object has a spectrum that peaks around 675 nm, whereas a white-hot object has a spectrum that has comparable intensities for all wavelengths in the visible region. The sun has a blackbody temperature of about 5750 K. Objects emit radiation at a//temperatures, not just at high temperatures. For example, night-vision goggles make infrared radiation emitted by objects visible in the dark. 

Planck s equation can be used to develop relationships among frequency, wavelength, and energy. By using this information, the relative energies of radiation on the electromagnetic spectrum can be compared. 

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Prelude to Quantum Theory Qrbitals of the Hydrogen Atom... 

Prelude to Quantum Theory—The study of electromagnetic radiation emitted from hot objects led to Planck s theory, which postulates that quantities of energy can have only certain values, with the smallest unit of energy being that of a quantum. The energy of a quantum is given by equation (8.2) = hv, where h is Planck s... 

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