Question

Describe the development of the quantum model of electromagnetic radiation

Answer 1

Quantum model of electromagnetic radiation:

The quantum nature of EM radiation and its interaction with matter.Although classical physics had explained most of its behavior as a result of its wave nature, Planck and Einstein showed that electromagnetic (EM) radiation behaves as if its energy is carried at the nanoscale in small bundles, or quanta (plural of quantum), of energy with particle-like characteristics. The behavior of EM radiation in its interactions with matter is, in fact, where this quantum nature is most clearly revealed.

We know that the light of the sun can provide a pleasant warmth, but overexposure of the skin to sunlight results in a burn. This burning, which suggests a light-induced chemical change, is due to the UV component of the sun's radiation. Our experience with sunlight conforms to the idea that EM radiation can deliver its energy to matter as it is absorbed. How this absorption occurs at the atomic and molecular scale cannot be accounted for by the wave model.

Black body radiation:

As anyone who has observed the glow of a hot iron will attest, matter emits EM radiation as a result of its thermal energy. When this is given off under idealized conditions it is called black body radiation. The emission spectra of black body radiation at different temperatures (see illustration below), which defied prediction by classical physics, could be explained if, for each frequency (recall that frequency is inversely proportional to wavelength), the possible energies of the oscillators (oscillating charges within matter give rise to black body EM radiation) were restricted to values proportional to integral multiples of the oscillator frequency.

that is, E = nhν,

where E is the energy of the oscillator and

ν is its frequency,

n is a positive integer (n = 1,2,3,...) ,

  h is a proportionality constant.

This implied the oscillators carried energy in discrete “packets” or quanta. This insight was due to German physicist Max Planck, who advanced his hypothesis in 1901. Planck chose the value of the proportionality constant h - which became known as Planck's constant (h = 6.6260688 × 10^–34 J·s) .

The development of after a long struggle electromagnetic wave theory had triumphed. The Faraday-Maxwell-Hertz theory of electromagnetic radiation seemed to be able to explain all phenomena of light, electricity, and magnetism.

The understanding of these phenomena enabled one to produce electromagnetic radiation of many different frequencies which had never been observed before and which opened a world of new opportunities. No one suspected that the conceptional foundations of physics were about to change again.