Dual Behaviour of Electromagnetic Radiation

The particle nature of light posed a dilemma for scientists. One the one hand, it could explain the photoelectric effect satisfactorily but on the other hand, this was not consistent with the known wave behavior of light which could account for the phenomena of interference and diffraction. The only way to resolve the dilemma was to accept the idea that light possesses both particle and wave-like properties, i.e., light has dual behavior. Depending on the experiment, we find that light behaves either as a wave or as a stream of particles. Whenever radiation interacts, with matter, it displays particle like properties, in contrast to the wavelike properties (interference and diffraction) it exhibits when it propagates. This concept was totally alien to the way the scientists though about matter and radiation and it took them a long time to become convinced of its validity. It turns out, as you shall see later, that some microscopic particles like electrons also exhibit this wave-particle duality.

There are three experiments in our syllabus which cannot be explained by wave nature namely

• Photoelectric Effect. 
• Compton Effect and 
• Black Body Radiations.

 The reason is that waves cannot transfer momentum into particles whereas these experiment involves the transfer of momentum. To explain this as wave nature couldn't particle nature was adopted. In a few cases like

• Diffraction, 
• Interference 

particle nature is violated and wave nature is satisfied. In the rest of the experiments both the natures can be used to explain the phenomena.

Keeping all these views in mind, Dual nature is predicts that when waves collides with matter it exhibits particle nature and when they don't they exhibit wave nature.