Cathode Ray Experiment
Cathode ray experiment is the experiment performed by J. J. Thomson that led to the discovery of the electron. It was one of the most important discoveries in the history of physics. In the experiment, J. J. Thomson took a tube made of glass containing two pieces of metal as an electrode. The air inside the chamber is subjected to high voltage and electricity flows through the air from the negative electrode to positive electrode.
Apparatus of the experiment
The apparatus of the experiment incorporates a tube made of glass containing two pieces of metals at the opposite ends which act as an electrode. The two metal pieces are connected with an external voltage. The pressure of the gas inside the tube is lowered by evacuating the air.
Procedure of the experiment
- Apparatus is set up by providing a high voltage source and evacuating the air to maintain the low pressure inside the tube.
- High voltage is passed to the two metal pieces so as to ionize air and make it a conductor of electricity.
- The electricity starts flowing as the circuit was complete.
- To identify the constituents of the ray produced by applying a high voltage to the tube, the dipole was set up as an add-on in the experiment.
- The positive pole and negative pole was kept on the either sides of the discharge ray.
- When the dipoles were applied, the ray was repelled by negative pole and it was deflected towards positive pole.
- This was further confirmed by placing phosphorescent substance at the end of discharge ray. It glows when hit by discharge ray. By carefully observing the places where fluorescence was observed, it was noted that the deflections were towards the positive side. So the constituents of the discharge tube were negatively charged.
The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube. Thus, we can conclude that electrons area basic constituent of all the atoms.
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