Gaseous discharge at various pressures
The experimental setup shows that gas discharge tube fitted with manometer and vacuum. IN normal situation air is bad conductor of electricity as a result discharge phenomena of gas cannot be observed. However, it is possible by using source of electricity of high voltage which can produce high electric field strength. The gas discharge at various pressure is explained as follows:
At pressure 5mm Hg
When the pressure is reduced to 5mHg the air inside the discharge tube appears in the form of luminous streak; anode and cathode. This luminous streak may appear in different colors which depends upon the nature of the gas present in the tube. The luminous appears in the tube is also called blue streamers.
At pressure 2 mmHg
When the pressure is reduced to 2mmHg the luminous streak becomes broad throughout the tube. The luminous streak at this pressure is said to be Geisslers discharge.
At pressure 1 mmHg
When the pressure is reduced to 1mmHg, luminous streak’s appears in the form of positive column which starts from anode towards the cathode.
At pressure 0.5 mmHg
When pressure is reduced to 0.5 mmHg, positive column becomes short and appears in the form of striaction which shifts towards anode detaching from cathode but another type of glow appears at the cathode known as negative glow. And the dark space between the negative glow and striaction is known as Faraday’s dark space.
At 0.1 mmHg
When the pressure is reduced to 0.1 mmHg negative glow, faraday’s darkspace and striaction moves towards the anode and another type of glow appears at the cathode called cathode glow and the dark space between cathode glow and faraday’s dark space is known as crooke’s dark space.
At 0.01 mmHg
When the pressure is reduced to 0.01 mmHg crooke’s dark space cover the entire discharge tube and the stream of negatively charged particles emerges from the cathode in the form of rays known as cathode rays.Hence, cathode rays are negatively charged particles which emerges from the cathode at reduced pressure of 0.01 mmHg .
At pressure 10-4 mmHg
When the pressure is reduced to 10-4 mmHg there will be no discharge in the tube because the air particles required for the ionization becomes insufficient inside the tube .
Characteristics of Cathode ray
- Catho rays are negatively charged particles emits from the cathode at reduced pressure of 0.01 mmHg.
- Cathod rays moves in a straight line and cast shadow of an object when incident on the object.
- Cathod rays ionizes the gas through which it pass.
- Cathod rays are deflected both by electric field and magnetic field.
- The velocity of cathode rays ranges from 1/30th to 1/10th velocity of light.
- Cathod rays when incident on the material having high atomic wt. produces x-rays.
- Cathod rays shows thermal behavior when passing through the medium.
- Cathod rays has penetrating power to few mm in paper coil as well as aluminium coil.
- The position of anode is independent inside the discharge tube to produce cathode rays .