Recently, I have stumbled upon a YouTube video by Veritasium describing the conductivity of fire. My question is: how exactly does fire conduct electricity? I am a high school student; therefore appropriate language is expected.
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4$\begingroup$ I believe you meant flame, which can contain ionized gas. That should conduct if a non-negligible number of charge carriers are present. $\endgroup$– liberiasCommented Nov 26, 2012 at 2:19
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1$\begingroup$ Related (nearly a duplicate): physics.stackexchange.com/q/23469/520. $\endgroup$– dmckee --- ex-moderator kittenCommented Jan 16, 2013 at 17:39
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$\begingroup$ FWIW, there are devices known as flame detectors; among their applications are safety devices in domestic furnaces. Some flame detector designs are based on the fact that a flame contains ionized gas (plasma) and is therefore conductive. $\endgroup$– Anthony XCommented Aug 20, 2013 at 2:52
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4 Answers
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This video illustrates how a candle flame conducts a high voltage (10,000 volts). Although the ion density is small in a candle flame, they are sufficiently present to conduct electricity.
answered Nov 26, 2012 at 4:17
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Fire is a plasma and plasmas conduct electricity. This is because in a plasma an important portion of the atoms are ions. This means that there are free charges on the plasma that move if a voltage is applied to the plasma, this creates a current.
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7$\begingroup$ Most sources don't consider the ion density in fire to be sufficiently high to be classified as plasma. However, at high voltages, electrical conduction can occur in spite of the low ion density. $\endgroup$ Commented Nov 26, 2012 at 17:45
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It basically conducts electricity the same way salty water does: both contain some concentration of charged particles that are free to move.
Water contains some concentrations of ions and protons (H$^+$ protons). When there is a voltage difference, the ions will move according to their charge.
The hot gas of the flame contains positively charged ions and electrons, which will move in the same way as the ions in the water. The reason there are ions is that the heat of the gas is such that some of the electrons can free themselves from the attraction of their atoms.
At the (relatively) low temperatures of a candle flame, not many electrons are free, but with sufficiently high voltage, you can get a good current. At much higher temperatures, there are so many free electrons and positive ions that physicists say the matter is in a 4th state: plasma. Plasma is found in stars, solar wind, fission reactors.
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actually, the fire does not conduct electricity, it simple ionises the air around it and the free electrons create a conducting path across the gap
