Sunday, February 1, 2015

Rutherford Alfa experiment and observations about Atom

Physics is a branch of science where we study nature. It deals with different properties of matter. We know that the matter has three different states like solids state, liquid state and gaseous state. All the states the matter consists of molecules. It is understood that molecules can be divided into atoms. When they were named as atoms, it means they are not divisible. But later we are able to divide atoms further into nucleus and the electrons which are revolving around the nucleus.

To know the structure of atoms, we have different theories and the corresponding experimental results.

We are having a model called pulp pudding model. It is also called watermelon model. According to this theory electrons and protons are uniformly distributed in the nucleus like the seeds of a watermelon. As this theory is unable to explain all the properties of matter, a new theory called Rutherford Alfa experimental model is introduced.

According to Rutherford Alfa experiment model nucleus is consisting of positive charges and the size of the nuclei is much smaller than that of the atom. To verify this, an experiment is performed. In this experiment helium particles are allowed to strike a thin gold foil. Helium particles consist of positive charge. As the gold foil is very thin, we can assume that helium particles can directly go and interact with the atom itself.

It is experimentally observed that, out of 8000 alfa rays that were driven towards the nucleus, only one is deviated. From that it can be concluded that the nucleus is also having a positive charge. Then only there will be repulsion and the alpha ray and nucleus so that path is deviated. It can also be concluded that the size of the nucleus is very small when compared with the size of the atom. That is why out of so many positive rays only very few are reflected.

As there is repulsion between the two positive charges, alpha particles cannot go and strike the nucleus. After they reach a certain distance, the repulsion dominates them so that either they deviates or reflects back. That’s why the particles are able to reach up to only a certain distance from the nucleus and this distance is called closest distance of approach. At that point all the kinetic energy of the alpha particle is converted into electrostatic potential energy between the Alpha particle and the protons of the nucleus.

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