Wave–particle duality is a fundamental concept in quantum physics which states that particles such as electrons and photons exhibit both wave-like and particle-like properties depending on the type of experiment being performed.

Light as a Particle

In the photoelectric effect, light behaves like a stream of particles called photons. Each photon has an energy given by:

\[ E = hf \]

• \(E\) = energy of the photon (Joules)
• \(h\) = Planck's constant (\(6.63 \times 10^{-34} \, \text{Js}\))
• \(f\) = frequency of light (Hz)

Light as a Wave

Light also shows wave-like behavior in interference and diffraction experiments. It has a wavelength related to its speed and frequency:

\[ c = \lambda f \]

• \(c\) = speed of light (\(3.00 \times 10^8 \, \text{m/s}\))
• \(\lambda\) = wavelength (m)
• \(f\) = frequency (Hz)

de Broglie Hypothesis

Louis de Broglie proposed that matter (like electrons) also exhibits wave-like behavior. The wavelength of a particle is given by:

\[ \lambda = \frac{h}{p} = \frac{h}{mv} \]

• \(\lambda\) = de Broglie wavelength (m)
• \(h\) = Planck’s constant
• \(p\) = momentum = \(mv\)

Experimental Evidence

• Photoelectric effect – shows particle behavior of light.
• Electron diffraction – shows wave behavior of particles.

Conclusion

Wave–particle duality reveals that classical ideas of "particle" and "wave" are not sufficient to describe quantum objects. Instead, quantum particles have a dual nature that depends on how they are observed.

Written by Thenura Dilruk