Page 254 - Essentials of physical chemistry

216 Essentials of Physical Chemistry

Thermometer
Slit
Fe

Lens
Prism

Film

Heat source
FIGURE 10.2 A schematic of measurement of blackbody radiation from a heated source.

FIGURE 10.3 Max Planck (1858–1947) was a German physicist who solved the problem of the blackbody
radiation curve by assuming energy is quantized which is the foundation of quantum theory. He is considered
one of the foremost scientists of the twentieth century and a number of research institutes in Germany are
named after him. He received the 1918 Nobel Prize in physics for his work. We have mentioned that Albert
Einstein encouraged Planck’s interpretation of quantization and here Planck is presenting the Planck gold medal
to Albert Einstein in 1929.

The Rayleigh–Jeans formula for the blackbody radiation curve failed disastrously for short wave-
lengths and high frequencies but Planck was perhaps motivated mostly by his interest in Wien’s
empirical ‘‘law.’’ At that time it was believed that there would be many tiny discrete oscillators in
the cube of metal shown in Figure 10.1 and these oscillators emitted light as a function of
temperature so we will follow the classical Rayleigh–Jeans derivation up to a point. Assume the