Yes, the equation E = hf, where E is energy, h is Planck's constant, and f is frequency, is applicable to particles other than photons. This equation is a fundamental principle of quantum mechanics known as the Planck-Einstein relation.
Originally, the equation was derived by Max Planck to describe the quantized nature of energy in the context of electromagnetic radiation, specifically for photons. According to Planck's theory, electromagnetic energy is quantized into discrete packets called quanta or photons, and the energy of each photon is directly proportional to its frequency (f).
However, subsequent developments in quantum mechanics revealed that particles other than photons also exhibit wave-particle duality. This means that even particles with mass, such as electrons or protons, can exhibit wave-like behavior and have associated frequencies. In quantum mechanics, particles are described by wavefunctions, and the energy associated with a particle's wavefunction can be related to its frequency through the equation E = hf.
For particles other than photons, the equation E = hf is generalized to include the concept of de Broglie wavelength (λ), which relates the momentum of a particle to its wavelength: λ = h/p, where p is the momentum of the particle. The energy of a particle is then given by E = hf = (hc)/λ, where c is the speed of light.
In summary, while the original derivation of the equation E = hf was for photons, it is applicable to particles other than photons as well, considering their wave-like properties and the relationship between energy, frequency, and wavelength in quantum mechanics.