Planck's relation, also known as the Planck-Einstein relation, is a fundamental equation in quantum mechanics that relates the energy of a photon to its frequency. It is given by the equation:
E = h * f
where E is the energy of the photon, h is Planck's constant (a fundamental constant in quantum mechanics), and f is the frequency of the electromagnetic wave.
The relation between energy and frequency is specific to electromagnetic waves because electromagnetic waves are a unique type of wave that propagates through the electromagnetic field. Unlike other types of waves, such as mechanical waves or sound waves, electromagnetic waves do not require a medium to propagate. They can travel through a vacuum or through various media, such as air or water.
The electromagnetic spectrum encompasses a wide range of wavelengths, from extremely short gamma rays to long radio waves. The specific wavelength of an electromagnetic wave is related to its frequency through the speed of light, c, according to the equation:
c = λ * f
where c is the speed of light, λ is the wavelength of the electromagnetic wave, and f is the frequency.
By combining the equations E = h * f and c = λ * f, we can derive the relationship between energy and wavelength for electromagnetic waves:
E = h * c / λ
This equation shows that the energy of a photon is inversely proportional to its wavelength. As the wavelength of an electromagnetic wave decreases, its energy increases. This relationship is fundamental to understanding the behavior of electromagnetic radiation, including phenomena such as the photoelectric effect, where the energy of photons determines the ability to eject electrons from a material.
In summary, Planck's relation gives the wavelength of electromagnetic waves because it is specifically derived from the unique characteristics and properties of electromagnetic radiation. It relates the energy of a photon to its frequency, and through the speed of light, it establishes a connection between the wavelength and energy of electromagnetic waves.