Weird Science

Electric Wind

Polish ver­sion is here

Elec­tro­sta­tics

Ima­gine a sphere made of a highly con­duc­tive mate­rial. In such a case, the charge on its sur­face will distri­bute itself evenly, as there is no rea­son for any region to have a higher con­cen­tra­tion than ano­ther.

Now, let's con­duct a tho­u­ght expe­ri­ment and con­si­der a con­duc­tor with a shape other than a sphere. The elec­tric poten­tial must be equal at every point on its sur­face. As a result, charge den­sity beco­mes inver­sely pro­por­tio­nal to the radius of curva­ture at a given point. The smal­ler the radius of curva­ture, the higher the charge den­sity.

A char­ged con­duc­tor with sharp edges tends to lose its charge easily. This occurs because the sharp edges have an extre­mely small radius of curva­ture, lea­ding to a very high charge den­sity. At such high den­si­ties, the sur­ro­un­ding air mole­cu­les become ioni­zed, allo­wing charge to be trans­fer­red to air par­tic­les. This pro­cess gene­ra­tes what is known as an elec­tric wind.

The prin­ci­ple behind this phe­no­me­non applies to both posi­tive and nega­tive char­ges. It is illu­stra­ted in the fol­lo­wing dia­gram:

Ilustracja

At the tip of the sharp edge, charge den­sity rea­ches its maxi­mum. When it beco­mes high eno­ugh, neu­tral gas mole­cu­les near the tip are ioni­zed, mea­ning they gain an elec­tric charge. Since like char­ges repel, these char­ged gas mole­cu­les are pushed away from the tip, cre­a­ting a direc­ted air­flow known as the elec­tric wind.

We can attempt to obse­rve this phe­no­me­non our­se­lves.

Expe­ri­ment

To gene­rate high vol­tage, we can use a Van de Gra­aff gene­ra­tor, a school elec­tro­sta­tic machine, or a ZVS high-vol­tage gene­ra­tor. For deta­ils on how to build a ZVS gene­ra­tor, I enco­u­rage inte­re­sted rea­ders to visit my dedi­ca­ted page on this device. In addi­tion, we will need a can­dle and a thin, shar­ply poin­ted wire to serve as the tip.

War­ning: I do not recom­mend using a ZVS sys­tem for begin­ners who lack expe­rience with high-vol­tage cir­cu­its. The out­put of this device can reach seve­ral tho­u­sand volts (kV), posing a serious risk of elec­tric shock. Mishan­dling it could result in severe injury. The author assu­mes no respon­si­bi­lity for any damage or harm that may occur. Pro­ceed at your own risk!

One out­put ter­mi­nal of the ZVS sho­uld be gro­un­ded, while the other is con­nec­ted to the sharp tip, posi­tio­ned facing the can­dle flame:

Ilustracja

When the power sup­ply is tur­ned on, high vol­tage is applied to the tip. As a result, an elec­tric wind emer­ges from the tip. This wind can push the flame to the side or even extin­gu­ish it, as shown in the fol­lo­wing video:

The tip is posi­tio­ned on the right side. The air­flow is strong eno­ugh to be felt by hand as a cool bre­eze. Addi­tio­nally, you may notice the distinct smell of ozone, a bypro­duct of ioni­za­tion.

The force of the elec­tro­sta­tic wind in this setup is so strong that it can easily blow away small Sty­ro­foam par­tic­les:

During the elec­tric wind phe­no­me­non, corona discharge also occurs. You can read more about this effect on this page.

This prin­ci­ple is applied in iono­cra­fts (elec­tro­sta­tic lifters) and corona spin­ner (descri­bed here). More recen­tly, the con­cept of elec­tro­sta­tic wind pro­pul­sion has been inve­sti­ga­ted as a poten­tial means of pro­pul­sion for small spa­ce­craft and inter­pla­ne­tary pro­bes.

Enjoy expe­ri­men­ting and have fun lear­ning! :)

Fur­ther rea­dings:

Marek Ples

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