Understanding Electric Discharges in Gas Tubes: Experiments and Atomic Structure

[manjuvenamma]

Can some one kindly explain or give a reference link that explains why it happens what it happens in electric discharges through gases like William Crookes expermient of 1870s and JJ Thomsons experiments with cathode rays? Covering also such important aspects such as what would have happened if we did not remove air/gas in the tube? Basically, I want to know how our present knowledge of atomic structure explains the experiments and its results?

 

[mikelepore]

http://en.wikipedia.org/wiki/Thermionic_emission
http://en.wikipedia.org/wiki/Cathode_ray_tube

 

[astrokreng]

Electric discharges in gas tubes, such as those observed in William Crookes' experiments in the 1870s and JJ Thomson's experiments with cathode rays, are a result of the interaction between high voltage electricity and the gas molecules in the tube. The gas molecules, which are made up of atoms, become ionized when they come into contact with the high voltage electricity, meaning they lose or gain electrons. This creates a flow of charged particles, known as an electric discharge.

The behavior of the electric discharge in gas tubes can be explained by our current understanding of atomic structure. Atoms are made up of a positively charged nucleus surrounded by negatively charged electrons. When an electric current is passed through the gas in the tube, the electrons in the gas molecules are excited and gain energy. This causes them to move away from the nucleus and create a plasma, which is a state of matter where the gas is ionized and contains free-moving charged particles.

In William Crookes' experiments, the electric discharge was observed to form a glowing spot on the opposite end of the tube from the cathode (negative electrode). This was due to the electrons being attracted to the positively charged anode (positive electrode) and colliding with gas molecules along the way, causing them to emit light. This emission of light is known as fluorescence.

Similarly, in JJ Thomson's experiments with cathode rays, the electric discharge was observed to produce a beam of particles (cathode rays) traveling from the cathode to the anode. This was due to the high voltage accelerating the electrons towards the anode, and the beam of particles was able to pass through the gas because it had been removed from the tube.

If the air or gas was not removed from the tube, the electric discharge would not occur as effectively. This is because the gas molecules would collide with the electrons, causing them to lose energy and preventing the formation of a plasma. The gas molecules would also absorb some of the energy from the electric current, reducing the voltage and limiting the movement of the charged particles.

In conclusion, our current understanding of atomic structure explains the behavior of electric discharges in gas tubes, such as those observed in William Crookes' and JJ Thomson's experiments. It is the interaction between high voltage electricity and gas molecules, and the resulting formation of a plasma, that produces the observed phenomena. Removing the air or gas from the tube is crucial for the formation of a strong and visible electric discharge.