The photon is considered a quantum of energy because it is the fundamental particle associated with electromagnetic radiation, including light. In the context of quantum mechanics, energy is quantized, meaning it can only exist in discrete, indivisible units called quanta. The photon represents the smallest possible amount of energy that can be carried by an electromagnetic wave.
According to the wave-particle duality of quantum mechanics, light and other forms of electromagnetic radiation exhibit both wave-like and particle-like properties. When considering light as a particle, each individual particle is called a photon. Photons have properties such as energy, momentum, and angular momentum, which are quantized in discrete values.
The energy of a photon is directly proportional to its frequency (ν) or inversely proportional to its wavelength (λ), as described by the equation E = hν = hc/λ. Here, E represents the energy of the photon, h is Planck's constant, c is the speed of light, and ν and λ are the frequency and wavelength of the electromagnetic wave, respectively. This equation shows that the energy of a photon is determined solely by the frequency or wavelength of the associated electromagnetic radiation.
In summary, the photon is considered a quantum of energy because it represents the smallest possible unit of energy associated with electromagnetic radiation, and its energy is quantized based on the frequency or wavelength of the wave it represents.