why the fluorescence was observed during the cathode ray experiment and why is it so that under low pressure gas becomes conducting?

CBSE Class 11-science Answered

why the fluorescence was observed during the cathode ray experiment and why is it so that under low pressure gas becomes conducting?

Asked by bharti | 30 Apr, 2013, 08:37: PM

Expert Answer

Cathode rays produce fluorescence in some materials. As they are energetic electrons, when they strike a certain substance or the glass wall of the discharge tube, this excites the atoms of the substance or the glass and cause them to emit light, a glow called fluorescence.

As the discharge tube is evacuated, the electrons at the cathode get attracted to the anode due to the high potential difference. Cathode rays are not seen when the potential difference is low or if the gas pressure is high. At low pressure, there is enough space between the gas atoms that the ions could accelerate to high enough speeds that when they struck another atom they knocked electrons off of it, creating more positive ions and free electrons in a chain reaction. The positive ions are all attracted to the cathode. When they struck it, they knocked many electrons out of the metal. The free electrons (cathode ray beam) are all attracted to the anode.

Answered by | 01 May, 2013, 11:09: AM