ABSTRACT
This chapter discusses some of the experiments that provided evidence that light, which we have recognized as a wave phenomenon, has properties that we normally associate with particles. It explains these phenomena and to understand the physical processes involved, some kind of a corpuscular theory of light is required. The chapter discusses briefly how the idea of the existence of discrete structures has been innovated in physics. The first idea of the existence of discrete structures referred to physics of materials and their electric properties. In a different area of physics, radiation spectroscopy experiments show that light emitted by hot solid or liquid exhibits a continuous spectrum. The chapter focuses on that the results of the experiments on photoelectric effect are in contradiction to classical wave theory. The wave theory of light leads one to anticipate that a long-wavelength light incident on a surface could cause enough energy to be absorbed for an electron to be released.
