Subject: Physics
If an electric current flows through a gas, it is known as electrical conduction or discharge in the gas. At normal temperature and pressure, the gases are good insulators of electricity. We can make a gas conducting
A tube used to study the electrical conduction through gases at low pressure known as discharge tube. The figure shows the experimental set up to study the discharge phenomenon. It consists of a strong glass tube about 0.5 m long and 0.04 m diameters, closed at both ends and provided with two platinum electrodes A and C, called anode and cathode respectively. The two electrodes are connected to secondary terminates of a powerful induction coil. The discharge tube in connected with a vacuum pump to reduce the pressure inside the tube is gradually reduced, using a pump the following phenomenon are observed as explained below.
Reference
Manu Kumar Khatry, Manoj Kumar Thapa,et al. Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.
S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.
If an electric current flows through a gas, it is known as electrical conduction or discharge in the gas.
A tube used to study the electrical conduction through gases at low pressure known as discharge tube.
When the pressure in the discharge tube is reduced to about 10 mm of Hg, the discharge is in the form of luminous streaks between the electrodes called blue streamers.
When the pressure in the discharge tube is reduced to about 5 mm of Hg, the blue streaks broaden out into a luminous column which bright and steady. The luminous column is called Geissler’s discharge.
When the pressure in the discharge tube is reduced to about 2 mm of Hg, a long luminous column appears from an anode to cathode called the positive column.
When the pressure in the discharge tube is reduced to about 1 mm of Hg, the positive column detaches itself from the cathode and moves towards the anode, a blue luminous glow appears at the cathode called negative glow.
A dark space appears between a positive column and negative glow called Faraday’s dark space.
The space between cathode glow and a negative glow appears dark and is called Crooke’s dark space.
In this range of pressure, the positive column shortens and breaks into alternative bright and dark disc called striations
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