Explain how cathode rays and anode rays are produced in discharge tube
Dear Student,
Cathode rays are produced when a high voltage is applied between two terminals in a low-pressure environment. In this low pressure, it is easier for the electrons to flow from the negative terminal and form a beam of negatively charged electrons, which can be bent, or deflected, by magnetic fields and electric fields. Cathode rays" are simply beams of electrons. The name exists because cathode ray devices predate the discovery of the electron. The sharp shadows produced by Crookes tubes meant that something was travelling in a straight line from the cathode down the tube, so they were named cathode rays.
The vacuum doesn't have much to do with the production of electrons, per se, but without high vacuum, the electrons collide with gas particles before they travel very far. If there's enough gas, you get a plasma rather than a beam of electrons. The electron beam is produced by thermionic emission in hot cathodes—electrons are liberated from a hot filament when the thermal energy is enough for electrons to exceed the filament's work function. In cold cathodes, electrons are released by field emission, where a large applied electric field allows electrons to tunnel away from a metal electrode.
The air inside the discharge tube is a non-conductor of electricity. So initially the tube looks intact. As the air pressure inside reduces, the gas starts ionizing. Since a potential difference is maintained inside the tube, when one gas atom is ionized, the electron escaping from it, ionizes other gas atoms. There a stream of positive ions and negative electrons gets created. These start moving towards cathode and anode respectively. And thus, in such way, anode and cathode rays are produced.
Regards
Cathode rays are produced when a high voltage is applied between two terminals in a low-pressure environment. In this low pressure, it is easier for the electrons to flow from the negative terminal and form a beam of negatively charged electrons, which can be bent, or deflected, by magnetic fields and electric fields.
Cathode rays" are simply beams of electrons. The name exists because cathode ray devices predate the discovery of the electron. The sharp shadows produced by Crookes tubes meant that something was travelling in a straight line from the cathode down the tube, so they were named cathode rays.
The vacuum doesn't have much to do with the production of electrons, per se, but without high vacuum, the electrons collide with gas particles before they travel very far. If there's enough gas, you get a plasma rather than a beam of electrons. The electron beam is produced by thermionic emission in hot cathodes—electrons are liberated from a hot filament when the thermal energy is enough for electrons to exceed the filament's work function. In cold cathodes, electrons are released by field emission, where a large applied electric field allows electrons to tunnel away from a metal electrode.
The air inside the discharge tube is a non-conductor of electricity. So initially the tube looks intact. As the air pressure inside reduces, the gas starts ionizing. Since a potential difference is maintained inside the tube, when one gas atom is ionized, the electron escaping from it, ionizes other gas atoms. There a stream of positive ions and negative electrons gets created. These start moving towards cathode and anode respectively. And thus, in such way, anode and cathode rays are produced.
Regards
