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The Kid Should See This

What happens to a flame in an electric field?

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What happens to a lit candle when it’s sandwiched between two active high voltage metal plates? Watch the flame as the E.H.T. (extra high tension) power supply is switched on in this Animated Science video: The electric field splits the flame in two opposite directions.

The video demonstration is especially useful because, as U.K.-based physics teacher Daniel Powell points out, most schools don’t have the equipment to replicate the required 25-kilovolts. It’s also a dangerous demo, “so you must take care and no pupils close to it.”

What’s happening here? From the video notes:

“The hot flame of the candle ionises the air molecules in its surrounding into positive and negative ions.

“The positive ions are heavier and move much slower. Thus, a larger portion of the flame follows the positive ions, moving towards the negative plate.

“The negative charge are electrons and are very much lighter than the positive ions. They move faster towards the positive plate and more easily.”

flame reaction in an electrical field

“Thus, the portion of the flame that follows the negative ions are much smaller and thinner. This practical really does need a 25kV supply to work well.

“Also in a uniform electrical field the electrical field strength (Vm-1) is E∝𝑉/𝑑 so when we move the electrodes closer they put out the flame as E∝1/𝑑 as the field strength is stronger.

“At the end we can see the soot on the negative electrode due to the ions from the flame.

It’s a great demo for separation of ions and electrons and evidence of charged ions. Also clearly the mass of the positive is more not that there are more, slip of the tongue!”

What will happen when the high voltage plates are moved closer to the flame?

a candle flame
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Watch this next: A waterless and chemical-free sound wave fire extinguisher.

Plus, more candles and videos about fire, including:
• Candle Chemistry – ExpeRimental
• What’s the chemistry and physics of a flame?
• Why Do Hot Things Glow?
• The Hidden Complexities of the Simple Match
• The Fire Lab and the Mysterious Science of Fire

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