Tesla Coils

[All Seeing Eye]

Why do Tesla Coils shoot off electrical sparks?

Would a Tesla Coil work in the Vacuum of space? would they still emit electrical sparks?

Since Electrons have a negative charge would a strong 'positive pole' magnetic field cause the electrons being emitted from the Tesla Coil to be deflected/repelled?
I read somewhere that if an Electron is moving and hits a magnetic field it gets deflected.

 

[Jadzia]

Why do Tesla Coils shoot off electrical sparks?

They generate extraordinary voltage by using a series of step up transformers. Step down transformers are like what's in your computer, taking mains down to 5 volts. These will happily work at 50Hz frequency that your mains comes in at. But step up necessitates using higher frequency alternating current. This is due to the induction equation...

Voltage Induced = -L * Rate of change in Current.
(where L is a constant.)

The faster you change current, (higher frequency) the bigger the right hand side, so the bigger the induced voltage is.

Tesla coils produce these very fast but short lived lightning bolts, that you perceive as the sparks.

Would a Tesla Coil work in the Vacuum of space? would they still emit electrical sparks?

Yes and no. Electricity looks different in space. What we see in the blue colour of nitrogen gas being ionised. In a partial vacuum electricity causes a glow rather than sparks: like with neon tubes. The principle is very similar in space; but you may not get any visible light in a true vacuum.

Since Electrons have a negative charge would a strong 'positive pole' magnetic field cause the electrons being emitted from the Tesla Coil to be deflected/repelled?
I read somewhere that if an Electron is moving and hits a magnetic field it gets deflected.

Yes. A magnetic fields will bend an stream of electrons. This is exactly what happens in a motor in fact. Just that the electrons are clinging to the wire as they flow.

The electrons don't care if they flow with a wire or without, they'll respond to a magnetic field in just the same way.

The electrons feel a force, causing them to turn in a circular arc in a plane at right angles to the magnetic field.

 

[Saturn0660]

60Hz here in the US..

 

[Jadzia]

OP and I are 50Hz.

 

[Alpha_Geek]

... but you may not get any visible light in a true vacuum...

...and here we have evidence that Jadzia was never old enough to have peeked inside a working electronic device that ran off vacuum tubes (or "valves" for you 50Hz Brits).

Your theory is correct. There would be no visible indication of current flow in a hard vacuum. Nixie tubes, the precursor to the LED display, had a reduced pressure atmosphere of neon or other gas that would ionize around the anode.

Vacuum tubes did have a glow inside them, but that was due to the heater filiament and not the actual current flow inside the tube.

 

[Alpha_Geek]

Yes. A magnetic fields will bend an stream of electrons. This is exactly what happens in a motor in fact. Just that the electrons are clinging to the wire as they flow.

This is also the phenomenon that allows a CRT based display to work. The electron beam is deflected in the X and Y axis by coils around the neck of the tube. The electron beam travels to the anode, where the colored phosphor dots live.


Another factor involved where high frequency AC is involved is "skin effect". A simplified explanation of this is that because the electrical current is changing direction so rapidly, it can't "chew" as deeply into the conductor. At the frequencies that a Telsa coil produces, it's not uncommon to see current flow as an arc along the exterior of a conductor. I've personally seen it travel down 1 leg of a resistor, around the casing of said resistor, and the back down the other leg to get to ground. It's all about the path of least resistance.

 

[Alpha_Geek]

...and FWIW, a Tesla coil is more than a coil. There's a circuit design to go along with it to produce the HF AC that makes it more than a mere transformer. The first hit on Google will lead to enlightenment.

CAUTION: DON'T FUTZ WITH THIS STUFF IN RL UNLESS YOU KNOW WHAT YOU'RE DOING! INJURIOUS, FATAL, OR HUMILIATING ACCIDENTS ARE BOUND TO HAPPEN.


...and anyone going to Dragon*Con should see & hear the singing Tesla Coils!! Mega cool in a ubergeek sort of way!

 

[Chaos Descending]

But step up necessitates using higher frequency alternating current. This is due to the induction equation...

Voltage Induced = -L * Rate of change in Current.
(where L is a constant.)

That's not strictly true. The main thing for a "step up transformer" is to have more coil turns on the secondary side than on the primary side. A "step down transformer" is easily turned into a "step up transformer" by wiring it backwards. There's no necessity for a higher frequency to make a step up transformer work.

Now it may be the case that a tesla coil specifically needs a higher input frequency, but that is not true of step up transformers per se.

 

[Jadzia]

So what is the role of frequency?

If I had a 12:240 turn transformer, and drove it with 12 volts at 0.01Hz, would you expect my multimeter to show a peak voltage of 240 volts (or thereabouts) across the secondary?

 

[Chaos Descending]

I don't know of any electrical grid in the world that uses 0.01Hz AC, so I'll ignore your example.

I do know for a fact that at 50 Hz (or 60 Hz even), a 12:240 transformer driven with 12V at the primary would definitely show 240V at the secondary.

And of course, you are right that voltage is the inductance times the time rate of change of current, but also remember that the two sides of the transformer do not have the same inductance due to the uneven number of windings. You get the step up effect not by varying frequency, but by varying inductance.

 

[Chaos Descending]

Remember, you said "But step up necessitates using higher frequency alternating current."

I'm not saying that a higher frequency wouldn't make the step-up work BETTER, I'm only saying that a higher frequency is not NECESSARY for step-up, since a winding ratio less than 1:1 will also do the job. You seemed to indicate that a step-up transformer would not be possible at 50Hz, and any novice electrician knows better than that.

 

[Jadzia]

In the context of a Tesla coil, step up does necessitate high frequencies. Or was Tesla doing it all wrong?

 

[Chaos Descending]

In the context of a Tesla coil, step up does necessitate high frequencies.

Or was Tesla doing it all wrong?[/QUOTE]

True indeed, only you didn't say that though. You said that a step down transformer works just fine at 50 Hz, but a step up transformer needs a higher frequency. That's patently wrong.

Step down transformers are like what's in your computer, taking mains down to 5 volts. These will happily work at 50Hz frequency that your mains comes in at. But step up necessitates using higher frequency alternating current.

I'm just calling it like I see it. Tachy... struggles with science enough without people inadvertently feeding him inaccurate information.

Or was Tesla doing it all wrong?

Did you not read the part up thread where I said "Now it may be the case that a tesla coil specifically needs a higher input frequency, but that is not true of step up transformers per se."

 

[Alpha_Geek]

This link will tell you about the role of frequency in AC circuits and components like transformers and coils. (Amusingly enough, there's a link to buy ST:XI on the page!)


.01 Hz?

You'd have to have a really funky coil for inductive reactance to be a factor that low!

Tesla Coils normally operate in the 40KHz to 1 MHz, range.

Hz = cycles per second. .01 Hz would be more akin to a fluctuation in DC voltage than AC.

The audio spectrum is roughly 20 Hz to 20 KHz.

I *think* they are switching the HF AC on and off with the audio signal to produce the audio in the "singing" Tesla Coils.

I've personally seen transformers that work in the audio spectrum for signal isloation, but going lower than that you really start to lose signal due to ineffiency.

Oh, one more thing, non-Tesla transformers work just fine in the 50 to 60 Hz range, they are employed everywhere to step the voltage power plants make and main lines transmit down to something that will woork in our houses.

 

[Silvercrest]

I don't know of any electrical grid in the world that uses 0.01Hz AC, so I'll ignore your example.

I think mine does. That's why my computer runs so slowly.

 

[Chaos Descending]

I don't know of any electrical grid in the world that uses 0.01Hz AC, so I'll ignore your example.

I think mine does. That's why my computer runs so slowly.

Maybe you should try powering it with a Tesla Coil.

 

[Silvercrest]

 

[Alpha_Geek]

Or maybe a Chambers Coil, although I am have been lead to believe that if they are improperly adjusted, spurious emissions from one can disrupt subspace communications.

 

[Chaos Descending]

I've heard that myself, so that's right out, and a Degaussing Coil wouldn't be much help either.

 

[Alpha_Geek]

...unless the metal frame around that CRT I mentioned earlier became magnetized. Then it'd be a grand thing to have!