22 Electric Fields

This page covers the electrical fields section of the course. 


22 Electric Fields Student Booklet

22 Electric Fields

Semolina and Electric Fields

22.4 Coulomb Law Challenge Questions

pHet Fields Worksheet

22.5 Uni Level Problems



Candle Flame in an Electric Field

When the E.H.T. power supply is switched on, the candle flame splits into two portions in opposite directions.

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.

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 if charged ions. Also clearly the mass of the positive is more not that there are more, slip of the tongue!

The demo is dangerous so you must take care and no pupils close to it. My EHT is current limited for safer use in schools.

Finally the video has one error when I talked about the ions there are clearly the same POS and negative ones. The masses are the differences.

Lastly it's quite hard to get the flame to go out, I was lucky...so don't be disappointed if you fail!
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