Nature of Matter
 
 

Niels Bohr On the previous page we saw that light has a dual nature. It is both a wave and a particle. However such characteristics surely seems strange a French scientist Louis De Broglie created the even stranger theory in 1924. He came to the opinion that if light could be sometimes described as a wave then maybe matter could be sometimes conceived as a wave.
He suggested that there is a wave connected with a moving particle. The length of that wave as he said is equal to:


 
 E = h*v      

Where h is Planck's constant, m is the mass of a moving particle, and v is its velocity. What comes of the formula is that a particle of smaller velocity and smaller mass is characterised by a longer wavelength.


De Broglie wave

Let's imagine two examples:

1) A baseball of a mass of 0,14 kg is thrown with a 40 m/s velocity by a pitcher. After placing the data to the formula we get a 1,2*10-34 m wavelength. It isn't much, actually even using the most modern technologies you wouldn't see it.

2) On the other hand an electron moving with a 40 m/s velocity has a 1,8*10-5 m wavelength. Such waves can be observed.






The de Broglie theory was experimentally confirmed in 1926 and 1927. It was done independently by two scientists. They were Clinton Joseph Davisson and George Paget Thomson (the son of the discoverer of an electron). Clinton in his experiment illuminated a nickel crystal with a beam of electrons. The crystal then began to emit electrons itself. The number of electrons emitted in different directions was defined using a collector that could rotate around the crystal. It turned out that electrons from the crystal plate were emitted at all directions but at some angles there were more of them. Clinton discovered that the phenomenon could be explained assuming the wave nature of electrons. This way the de Broglie hypothesis was confirmed.


The Davisson's experiment


The second scientist who at about the same time confirmed the wave theory of matter was George Thomson. In his experiment he used a thin metal foil at which he pointed a beam of high speeded electrons. The electrons went through the foil. On a screen behind the foil the places where electrons fell were seen. The picture that appeared on the screen was a number of rings. It was caused by diffraction, the phenomenon characteristic for waves. Diffraction proceeded as electrons were passing through the foil.


The Thomson's experiment

Not long later scientists conducted some more experiments proving that particles other than electrons have also wave nature.

Let's sum up the knowledge gained on the last few pages. Light, as Niels Bohr suggested, has dual wave-particle character. Sometimes it shows its particle characteristics and some other times the wave one. A particle of light is called the photon. Photon transfers energy that is proportional to the light wavelength. That fact explains the course of the photoelectric effect. Matter also has a dual wave-particle nature. Louis De Broglie suggested that. His hypothesis was soon confirmed experimentally. The wavelength of a particle is inversely proportional to its velocity and its mass. The heavier object it is the shorter wave it has. Thanks to that in the macroscopic world we live in we don't see the phenomena of the wave nature of matter; for example it would be very, very hard for us to undergo interference, although it is theoretically possible.


 

REMEMBER:
Matter has dual character.
With every body there is connected some wave.
The lower mass and the lower velocity the body has, the longer is its wave.
Louis De Broglie created the theory of the dual nature of matter.

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   TEST no. 3

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