Home Science Atom

de Broglie Relation

de Broglie Hypothesis and Relation

de Broglie relation of wavelengths pointed out that just as photon light has both particle and wave nature, electrons have also these duel properties of matter. de Broglie’s hypothesis suggested that electron travels in waves with the definite wavelength, frequency. Therefore, the de Broglie equation given from mass energy relation and plank quantum theory used to calculate and convert the wavelength and frequency of electromagnetic radiation.

This wavelength relation tested by Davisson Grammar experiments and Bohr’s theory of hydrogen atom. Hence de Broglie hypothesis led from the consideration of quantum theory and formula of relativity by Einstein equation in physics.

de Broglie wavelengths, frequency and energy relation for light photon or electron

de Broglie Equation for Wavelength

de Broglie proposed an equation with the help of the Plank equation and Einstein energy mass law of matter. He considered the mass of the photon and wave nature of photon light quanta with wavelength = λ, frequency = ν, and energy = E.

E = hν = hc/λ
where c = velocity of light
h = Plank constant = 6.627× 10-27
Theory of relativity from Einstien
E = m c2.
Combining these two relations,
mc = h/λ
or, p = h/λ
where p = mc = mv = momentum.
∴ Wavelength (λ) = h/p

de Broglie relation extended light particle to the dynamics particle of matter and calculate the mass, momentum, wavelength frequency, and energy of electron.

λ = h/p = h/mv
where m = total electron mass
v = velocity.

Bohr’s Theory and de Broglie Relation

Angular momentum of moving electrons in Bohr’s model

mvr = nh/2π
or, mv = nh/2πr
where m = mass of an electron,
n = principle quantum number = 1, 2, 3, 4, …
r = radius of the orbital of an atom.
According to de Broglie’s equation
λ = h/mv
or, mv = h/λ
where λ = wavelength of the moving electron.
Combining de Broglie equation and Bohr’s theory
2πr = nλ

Therefore, a standing wave is fixed within the space allowed to it and does not travel beyond the allowed space. It does not travel beyond the allowed space.

Electron Diffraction Experiment

Within the few years of de Broglie’s hypothesis, Davisson and Germer tested these predictions formula by diffracting electrons by crystals. The diffraction is similar to the diffraction of x-ray radiation. Therefore, they established that a beam of electrons really has wave properties along with particle properties. The wavelength associated with electrons of known momentum value was exactly the same that predicted by the de Broglie wavelength equation, λ = h/p. This relationship applies to all particles but for heavy particles, the wavelengths are too small to be observed experimentally.

Kinetic Energy and Wavelength

When the particle-like light photon or electron is subjected to the potential energy difference V to acquires a velocity v then it has two types of energy potential and kinetic energy. Therefore, the energy of an electron, E = Ve = ½ mv2, where e is the charge of an electron. Hence wavelength (λ) = h/√2mVe, This is the derivation between emission kinetic energy and de Broglie wavelengths relation of photon or electron.