Physics Lesson 15.8.5 - Electric Current in Gases

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Welcome to our Physics lesson on Electric Current in Gases, this is the fifth lesson of our suite of physics lessons covering the topic of Miscellaneous, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

Electric Current in Gases

In normal conditions, gases are insulators. When a gas is heated, the kinetic energy of its molecules increases. When this kinetic energy exceeds the binding energy (i.e. the energy that keep electrons bound with the atoms), electrons escape from atoms and as a result, atoms begin to ionise. If the temperature of gas is high enough, the gas becomes a mixture of positive ions and free electrons. Such a state is known as plasma and it represents the fourth state of matter besides solid, liquid and gas states we have explained earlier. A material in plasma state is a good conductor of electricity as it contains a lot of free charges.

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Heating the gas is not the only method to obtain free charges. Electromagnetic radiation is another factor that produces electric current in metals due to ionization of gas particles, as shown in the figure below.

A third factor that can cause gas ionization (and therefore an electric current) is a high potential difference produced due to the existence of an electric field inside the gas. For this, a power source such as a battery is needed. Electrons accelerate due to the electric field and gain a high kinetic energy over a small distance. When electrons strike the gas atoms, they pull out new electrons from atoms turning them into positive ions. This kind of ionization is called discharge by self-ionisers. Look at the figure below.

The phenomenon of discharge by self-ionisation is used to construct light bulbs and self-illuminating structures such as billboards, light tubes etc.

You have reached the end of Physics lesson 15.8.5 Electric Current in Gases. There are 5 lessons in this physics tutorial covering Miscellaneous, you can access all the lessons from this tutorial below.

More Miscellaneous Lessons and Learning Resources

Electrodynamics Learning Material
Tutorial ID	Physics Tutorial Title	Revision Notes	Revision Questions
15.8	Miscellaneous
Lesson ID	Physics Lesson Title	Lesson	Video Lesson
15.8.1	Measurement of Current and Voltage
15.8.2	Superconductivity
15.8.3	Electric Current in Liquids
15.8.4	Faraday's Law for Electrolysis
15.8.5	Electric Current in Gases

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