DISCOVERY OF ELECTRON IN FULL DETAILS


The existence of electrons in an atom was show by j.j Thomson in 1897 . Thomson passed electricity at high voltage through a gas at very low 
pressure taken in a discharge tube. Streams of minute particles were given out by the cathode  (negative electrode). These stream of particles are called cathode rays
(because they come out to cathode). the mass and charge of the cathode ray particles does not depend on the nature of gas taken in the discharge tube.
 Cathode rays consist of small , negatively charged particles negatively charged particles called electrons.
Thomson explained the formation of cathode rays as follows. The  gas  taken in the discharge tube
consists of atoms, and all the atoms contain electrons. when high electrical voltage is applied, the electrical energy pushes out some of the electrons from the atoms of the gas.
These fast moving electrons form cathode rays. thus, the formation of cathode rays chow that one of the subatomic particle present in all the atoms is the negatively 
charged 'electron'. We can now define an electron as follows.

the electron is a negatively charged particle found in the atoms of all the elements. The electrons are located outside the nucleus in an atom. only hydrogen atom contains

one electron, all other atoms contain more than one electron. An electron is usually represented by the symbol (e-) e for electron and minus sign for negative charge.


Characteristics of a electron

1.  charge of an Electron.  The absolute charge on an electron is 1.6*10^-19 coulomb of negative charge. now, 1.6*10^-19 coulomb has been found to be the smallest negative charge carried
by any any particles. so, this is taken as the unit of negative charge. this means that an electron has 1 unit of negative charge. In other words, the relative charge of an electron is ,
-1(minus one).

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