Question 7: What is meant by wave-particle duality? Explain.
Light exhibits the properties of interference and diffraction; so must have a wave nature! But the photoelectric and Compton Effects prove that light (more precisely, electromagnetic radiations) interacts with matter and exchange energy. This is purely a particle nature of light.
- Wave theory says the energy radiated spreads out continuously (i-e, without any breaks) in the form of waves.
- Quantum theory says the energy does not emit continuously but in small packets, called quanta. Each packet or quantum consists of energy hf; where f is the frequency of oscillation and h is the Planck’s constant.
Now some experiments support the wave nature of electromagnetic radiations and the others their particle nature. Both the proofs are strong enough and cannot be easily rejected.
The fact is both are right!
When the radiations interact with large or macroscopic particles, they behave like a wave and when radiations interact with small or microscopic particles (like electrons, protons etc), they behave like a particle. This means light has dual nature.
Not contented with only theoretical arguments, Davisson-Germer and G-P Thomson carried out experiments which revealed the wave-like nature of electron; originally considered to be a particle. J J Thomson had already found an e/m ratio for electron. This shows dual nature of particle, too.
Both these assertions lead to the conclusion that matter and radiations both have dual wave-particle nature. This concept is known as wave-particle duality.
This should be noted that one set of properties of either wave or particle is exhibited at a time. It is not possible we observe both characteristics at the same time.