Photon vs Phonon
Phonon and photon are two very close words, which can be mistaken for the same thing. A photon is a packet of energy, which is the base of quantum mechanics. A phonon is the collective oscillation of several atoms. Both of these concepts are very important in physics. Photon theory is the underlying theory that most of the modern physics is dependent on. Phonon is also an important concept in studying materials and their internal oscillations. In this article, we are going to discuss what phonon and photon are, their similarities, their definitions, applications of phonon and photon and finally the difference between photon and phonon.
What is Photon?
Photon is a topic discussed in wave mechanics. In the quantum theory, it is observed that waves also have particle properties. The quantum theory of light suggests that light travels in bundles of waves. Each of these wave packets behaves as a particle. The photon is the particle of the wave. It is a fixed amount of energy depending only on the frequency of the wave. The energy of the photon is given by the equation E = h f, where E is the energy of the photon, h is the Plank constant, and f is the frequency of the wave. Photons are considered as packets of energy. With the development of relativity, it was discovered that waves also have a mass. This is because waves behave as particles on interactions with matter. However, the rest mass of a photon is zero. When a photon is moving with the speed of light, it has a relativistic mass of E/C^{2}, where E is the energy of the photon and C is the seed of light in a vacuum.
What is Phonon?
In condensed matter such as solids and some liquids, the material displays elastic behaviors in atomic level. The bonds between atoms and intermolecular bonds are elastic. This causes the atoms and molecules to oscillate. The collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter are known as a phonon. A set of such oscillating particles are often referred as a quasiparticle. In quantum mechanics, an electron oscillating inside a bond is considered as a onedimensional quantum well. Since a quasiparticle is a collection of such electrons, it can be considered as a twodimensional or three dimensional quantum systems. A phonon is a special type of vibration in the lattice where every particle oscillates with the same frequency. This is known as the normal mode in classical mechanics. This is very useful in using the Fourier theorem to calculate the frequencies of arbitrary lattice movements in terms of the fundamental frequency.
What is the difference between Phonon and Photon? • A photon is a form of energy but the phonon is a mode of oscillation that occurs in lattice structures. • A photon can be considered as a wave and a particle, which are physically observable entities. A phonon is a mode of vibration, which is neither a wave nor a particle.

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