Science Articles

FACTS & THEORIES ABOUT DUAL NATURE OF LIGHT

Isaac Newton, in 1670, established that the perfectly straight lines of reflection demonstrate the light’s particle nature since only particles can travel in such straight lines. He explained refraction by saying that the particles of light accelerate laterally when they enter a denser medium.


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With scientific evidence present, it has been established that light has a dual nature. The dual nature of light states that:

  • Sometimes, the light acts like a photon (i.e. Particle) which helps in explaining the phenomenon of how light travels in the straight lines.
  • And also, sometimes, light acts like a wave which helps in explaining the phenomenon of how light can diffract or bend around an object.

THE THEORIES:

Isaac Newton, in 1670, established that the perfectly straight lines of reflection demonstrate the light’s particle nature since only particles can travel in such straight lines. He explained refraction by saying that the particles of light accelerate laterally when they enter a denser medium.

Robert Hooke, Christiaan Huygens, and Augustin-Jean Fresnel mathematically showed that light travels at different speeds in different media. Refraction was stated as the propagation of light waves, dependent on the medium.

Thomas Young, in 1803, discovered the double-slit interference. Since it explained the polarization phenomena, his experiment could establish the wave nature of light.

THE EVIDENCE

The dual nature of light was soon found to be a characteristic of the electrons. The evidence for the establishment of light as waves was established before and with the discovery of photoelectric effect, the particle nature of the light was established as well. The particle property of electrons was established by the De Broglie hypothesis and the following experiment by Davisson and Germer resulted in establishing the wave nature of electron.

DE BROGLIE HYPOTHESIS

De Broglie said that as light has a dual nature of being a wave and a particle, it must also have the characteristics of both. He establishes that the wavelength is inversely proportional to the momentum of a particle.

PHOTOELECTRIC EFFECT

The observations of this experiment were:

  • Without any time lag, the electrons got emitted.
  • By increasing the number of photoelectrons, one could only increase the intensity of light and not their maximum kinetic energy.
  • Even at varied intensities, the red light does not cause ejection of electrons.
  • Violet light would eject only few electrons but the maximum kinetic energies are greater than that of the lights of longer wavelengths.

DAVISSON-GERMER EXPERIMENT

It was conducted by Clinton Davisson and Lester Germer in 1923-1927. This was the very first application to the particle waves. It demonstrated the wave nature of matter and established the theory of wave-particle duality.