Wave Particle Duality: De Broglie Wavelength, Newton’s Corpuscular Theory

Wave Particle Duality postulates that matter as well as light exhibits both wave and particle nature. This phenomenon is proven not only for elementary particles but for compound particles as well like atoms and molecules. Different phenomena presumed different nature of light to explain the concept like the photoelectric effect of light presumed light as particles to explain the phenomenon whereas phenomena like interference and diffraction presumed light as waves. Altogether phenomenon can be explained with wave-particle duality. 

Key Terms: Wave nature, Huygens wave theory, Newton’s Corpuscular Theory, Wave, Atoms, Molecule, Phenomenon, Quantum physics, Light, Photoelectric effect

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What is Wave-Particle Duality?

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Wave-particle duality is the concept of quantum physics. According to this concept matter and light exhibit the characteristics of both waves and particles. It is like at one moment it acts as a wave whereas at another moment it acts like a particle.

Wave-Particle Duality

Wave-particle Duality in Matter

Just like light, matter also exhibits wave-particle duality. When the particle size is comparable to the wavelength, it may take over the properties of waves. Huge objects exhibit very small wavelengths so they cannot exist in the form of waves. However, the wavelength of small objects is comparable and significant to think of them as waves.

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Difference Between Wave and Particles

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To understand wave-particle duality it is necessary to know the difference between waves and particles.

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Theories of Wave-Particle Duality

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The duality of light has been there for a long time. 

Einstein’s Wave-Particle Theory 

Albert Einstein suggested that light does not behave exactly like a particle or wave. Preferably, it behaves as both wave and particle. In 1905 he proposed the wave-particle theory of electromagnetic radiation that states electromagnetic energy is released in discrete packets of energy called photons.

Theory of Louis de Broglie 

In 1924, Louis de Broglie proposed that particles can take over the properties of waves. He developed a theory of electron waves which was proved true when electron beams were directed at crystals and patterns of diffraction were observed. Electrons are particles and the phenomenon of diffraction can be explained in terms of waves only. Diffraction with electron beams proved that particles can take over the properties of waves.

He further proposed the equation that relates the momentum of a particle (p) with wavelength (λ).

λ= h/p

The modern wave-particle duality starts from Huygens and Newton's duality of light when they proposed competing for theories of light. Huygens thought light consisted of waves and Newtons considered light to be made of particles.

Newton’s Corpuscular Theory 

Isaac Newton further developed the corpuscular model proposed by Descartes. It presumes that light energy is consolidated in tiny massless elastic particles called corpuscles. Newton argued that these corpuscles reflect from the smooth surface of the mirror at the time of reflection as a ball bouncing from the plain smooth surface.

The theory was not able to explain some phenomena like color formation due to the thin film of oil on water. In some cases, Newton assumed the energy of all corpuscles to be the same and in other cases different, to explain partial reflection he argued that some corpuscles reflected and some transmitted as they have different energy. Such a problem does not occur with the wave nature of light.

Huygens Wave Theory 

He proposed that every point in the wavefront of light in a vacuum or transparent medium could be considered as the new source of wavelets (spherical wave) that expands in every direction at a rate depending upon the velocity.

Compton Effect 

In 1922 Arthur Compton observed scattering of x-rays from electrons while targeting carbon. The wavelength of the scattered x-rays was found to be longer than those incidents on the target. Compton effect could be explained only if a light had wave-particle duality.

Quantum View of Light

The Quantum theory of light was proposed by Einstein. It brings the concept of photons. According to this concept, the light travels in bundles or packets of light known as photons. The energy of each photon is given by hf, h is Planck's constant, and f is the frequency of vibration of that photon.

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Things to Remember

• The phenomenon of reflection and refraction can be explained by both the wave and particle nature of light. Interference, diffraction, and polarization can only be explained with the wave nature of light. The photoelectric effect can only be explained by the particle nature of light.
• Wave-particle duality is the concept of quantum physics. According to this concept matter and light exhibit the characteristics of both waves and particles.
• Huygens and Newton proposed competing for theories of light. Huygens thought light consisted of waves and Newtons considered light to be made of particles.
• Louis de Broglie proposed that particles can take over the properties of waves and proposed the equation that relates the momentum of a particle (p) with wavelength (λ), λ=h/p. Here “h” is Planck's constant.

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