Physlet® Quantum Physics 3E: The Need for a Quantum Theory

Chapter 4: From Blackbody to Bohr

The late 1800s and early 1900s saw physics move from the classical period (described by Newton's laws and Maxwell's equations) to what we now call modern physics (explained by special relativity and quantum theory). The shift to a quantum theory was prompted by a series of experiments that could not be adequately explained classically. These experiments include blackbody radiation and a number of experiments that placed the atom on center stage. This period also marks the beginning of our current understanding of the fundamental structure of matter. This chapter describes these experiments and developments ends with the Bohr model of the atom or the so-called old quantum physics. While the Bohr model and the other models were amazingly successful at explaining a number of atomic properties, the observations these models could not explain hinted at the need for a better theory (quantum mechanics).

Chapter 5: Wave-Particle Duality

Waves and particles each have unique properties, often properties that are mutually exclusive. But light, classically considered a wave, sometimes behaves like a particle (which we call a photon) and the electron, classically described as a particle, sometimes behaves like a wave. This chapter explores the evidence for wave-particle duality of light and electrons (as well as all other particles), the implications, and possible ways of understanding this duality. In the process, we also introduce and begin to explore the uncertainty principle: the position and the momentum of a particle cannot both be known precisely at the same time.

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