Wave nature of lightThe scientists
Max Planck and
Albert Einstein made great progress in the early 1900's in understanding the properties of
light in terms of particles known as
photons where the
energy of the photons depended on the
frequency (wavelength) of the light wave. These studies are the basis for the branch of physics that is known as quantum physics.
Calculating energy of light emitted by excited hydrogen atomsInspired by the work of Planck and Einstein,
Neils Bohr developed an empirical equation that enabled
calculation of the
energies of light emitted when
hydrogen gas is compressed and electrified. Unfortunately Bohr's equation
could not predict the frequency of light emitted from
elements other than hydrogen.
Recognising the wave-particle duality of the electron and confirming it by experimentLouis de Broglie sought to expand Bohr's work and, while doing so, hypothesised that all matter (not only photons) had a wave properties. He developed an
equation that allowed
calculation of wavelength of any object from Planck's constant and the mass and velocity of the object. This relationship was very important because it could be tested by experiment. The
experiments that
confirmed de Broglie's hypothesis were carried out three years after the equation was proposed.
Planck's constant is very small (6.63 × 10–34 J s). For the wavelength of an object to be in the range where the wavelength can be measured(10–12 m to 10–2 m) the product of the mass and velocity of the object must be very small (10–32 to 10–22) as for small particles like electrons and neutrons.
Macroscopic (objects that we can see) have a large mass relative to Planck's constant. Therefore their wavelength is very small relaitve to the object and cannot be measured. Thus the wave-properties of large objects are not observable.
The importance of de Broglie's work that established the wave-particle duality of the electron is that it suggested that the properties of the electron could be described using equations used to describe waves. This was a major breakthrough because this enabled development of equations that went beyond that of Bohr and enabled calculation of electron energy for any atom.