Insulating Materials

[soccersparks]

Hi,
I am doing the project How far can Sparks Jump. In the Materials it says i need to use some sort of insulating materials. Why do I need to use insulating materials? What effect does that have on the project?
Thank you,
soccersparks

[bradleyshanrock-solberg]

Two reasons.

The obvious one is safety. Electricity can be dangerous and you will want to be protected from whatever current you are experiementing with. Generally spark experiments can be done safely using low current, high voltage power sources. (something like a 9 volt battery, instead of your wall plug). Sparks are about voltage and resistance, not about current, and current is what burns or kills you.

In absence of insulation, there is no spark...electricity just travels through whatever medium it is, going from positive to negative charge.

Generally, electricity is all about having a positive charge and either a negative charge or a "ground", called that because literally it is a connection to the ground, the earth. Electrons want to flow from positive to negative or positive to ground. If there is no insulator, they just do so. If there is an insulator in the way, they don't. If the insulator is a gas though, how good a job it does depends on the amount of gas between the positive charged item and the ground. If you get closer, it stops being a good enough insulator to stop the electrons from flowing and you get a spark.

The most dramatic example of this is lightning. Charge builds up in the clouds. It tends to strike a point that is high...a tree or a church spire....less airbetween the cloud and the ground. Lightning rods work because they're more attractive to the electrons than most other substances, but you still have to place them so they're high relative to other things in the area. They're optomized to attract lightning but aren't THAT much better than everything else if they aren't at similar height.

[Louise]

In a new thread, the student asked about the placement of the insulation. I am moving the discussion back to this thread, and answering the question.

We are discussing this experiment:
https://www.sciencebuddies.org/science- ... ?from=Home


One of the variations is to insert material between the electrodes and see if it prevents the spark/ changes the distance. (Step Air itself is an insulator, you can have enough electricity to "break down" the insulating material. This is the spark, or lightening- the break down of air. This is you testing insulation by observing the effect on the spark.

Generally, when you do electrical projects you use insulation so you don't have electricity going where you don't want it. If you solder wires together, or splice cables together, you would then insulate them. Every cable/cord you have is covered with plastic insulation. Nothing is a bare wire.

In this project, you aren't building the fire starter from stratch, so the device insulation is already there. Look carefully at the fire starter- only a few parts are exposed metal- where the electricity is supposed to come out.

Louise

[soccersparks]

Hi,
Ok so in the explanation it says that the object is to see how many volts are produced. Well i know we are finding the distance of the spark but how is that related to finding how many volts are produced? That is what this experiment is about right? Have a good day!
Thank you,
soccersparks

[bradleyshanrock-solberg]

There is a formula for voltage and spark length. It's been 20 years since I had to know this stuff but a quick Google search turned up support for my memory from my electromagnetics classes.

Paschen's Law connects air pressure, voltage and spark length.

Here's a link that talks about the background and limitation of this "Law".

http://home.earthlink.net/~jimlux/hv/paschen.htm

The research portion of your project is intended to find out these kinds of relationships before you do the experiments, so you know the meaning of what you are attempting to measure and whether it connects to your question.

[Louise]

One of the variations is to insert material between the electrodes and see if it prevents the spark/ changes the distance. (Step Air itself
Louise

Looking at the post, I see the software changed my text- ( Step 8 ) to a face. Sorry for any confusion.


Louise

[soccersparks]

Hi,
Thank you for the response. But I am still sorta confused with the formula or how to figure out how many volts are produced. Thank you for all of yor time!
Soccersparks

[bradleyshanrock-solberg]

I suspect the difficulty you are having is that you have not yet been taught algebra. It generally is not taught until 9th grade.

The formulas in the link I attached assume you know how to read them and make use of them. The idea is that if you know the gas involved (air) the pressure (whatever air is at sea level probably, depending on where you live - Denver is different from Los Angeles) and the distance of the spark, you can calculate the voltage using the formulas and constants in the Paschen's Law link I provided.

That would only be a rough estimate. I'm not certain that your assignment is really intended to go down that road, so my best advice is to take the Paschen's Law web page, print it out, take your experimental results and go talk to your instructor about whether this is what he or she had in mind and get some help with the math if it is the right basic idea.

[soccersparks]

Hi,
Do all i need to have for my project is the equation V=30pd+1.35kV ? And in that equation what does the kV stand for?
Thank you,
Soccersparks

[bradleyshanrock-solberg]

kV = Kilovolts, which is the units he's using throughout his article. If you plug in the values for "p" and "d' the result for V will be in kilovolts.

A kilovolt is 1000 volts.

The 1.35 is a constant. "V", "p" and "d" are variables.

[soccersparks]

Hi,
Ok I did an example of using the formula below. Can you tell me if i did it right? And also what does the 30 stand for in the formula?

V=30pd+1.35kV

-The distance between the metal spheres is 10cm. The distance the spark jumped was 4cm.
V=30pd+1.35kV
V=30(4)(10)+1.35
V=1201.35 kiliovolts
Did i do that right? Let me know what i did wrong!
Thank you,
Soccersparks

[bradleyshanrock-solberg]

30 is just another constant.
p = pressure in atmospheres, (not distance between the two balls)
d = distance in cm (this is the spark distance)

So the basic formula is 30*1*4+1.35 = 121.35 kV. (actually should be expressed as 120 or 100 volts, see below)

However you need to be aware that the formula provided has some restrictions and if they apply, you have to go deeper than the basic formula.

"For air, and gaps on the order of a MILLIMETER, the breakdown is roughly a linear function of the gap length: V = 30pd + 1.35 kV"
"Typically, the Townsend mechanism (and by extension Paschen's law) apply at pd products less than 1000 torr cm, or gaps around a centimeter at one atmosphere."

Your gap was 4cm at 1 atmosphere (or pd product = 3040 torr cm, there are 760 torr in one atmosphere). This means the basic formula is too simple and we have to go down to the more complex stuff below.

Vbreakdown = B * p * d / (C + ln( p * d))
B = 365, p = 1, d = 4, C = 1.18 in air

When I run that formula on my spreadsheet I get 819.2766. I'm not sure how accurate your centimeter and atmosphere measurements were. If the pressure was 1.0 atmospheres and the distance was 40 millimeters (4.0 centimeters) then you can express this result as 820 volts. If as is more likely you know the pressure was roughly 1 atmosphere and the distance was roughly 4 centimeters (not 3, not 5) then you really should express the result as 800 volts. (this rounding is a concept called "significant digits" and is used whenever your result is much more precise than your measurements. If you have pretty good confidence that your pressure was closer to 1.0 atmospheres than 1.1 or 0.9 and that your spark was closer to 40 millimeters than 41 or 39, then 820 is the better number to use)

I must say that this seems quite complex for grade 6-8. I'm also a bit concerned that I pulled the above formulas off the web and your instructor might intend you to use another more authoritative reference. Keep in mind that the article has many qualifications on the accuracy of the formulas:

"but it should be realized that there are many, many factors which have an effect on the breakdown of a gap, such as radiation, dust, surface irregularities. Excessive theoretical analysis might help understanding why a gap breaks down, but won't necessarily provide a more accurate value for the breakdown voltage in any given situation."

"Note that the sparking voltage is affected by the electrode material, with cathodes of Barium and Magnesium having higher voltages than Aluminum, for example."

"Paschen's law ( V = f(pd)) should really be stated as V = f( Nd) where N is the density of gas molecules, which is, of course, affected by the temperature as well as the pressure of the gas ( n/V = p/RT). "

"In air, increasing humidity increases the breakdown voltage."

[bradleyshanrock-solberg]

The more complex formula that returned ~820 volts is expressed more neatly as

V = 365*p*d/(1.18+ln(p*d))

I don't know if you have had logarythms yet, but "ln(1*4)" = 0.602059991 according to Excel "=log(1*4)"
You could look it up on a log table or use a calculator for that value too, if you know what the notation means.

[deleted-2574]

Hi soccersparks,

I'm jumping in here in the middle to make 2 comments.

Assuming V=30pd+1.35kV

is the correct equation:

1. Your use of the equation is correct.

2. One would normally write the equation as V=30pd+1.35

The "V" on both sides of the equation is visually confusing.
I know they are different "V"'s.

Someone else will need to comment if the equation is correct.

[soccersparks]

Hi,
IN my project what is the Pressure in atomosphere?
Thanks,
Soccersparks

[bradleyshanrock-solberg]

Hi,
IN my project what is the Pressure in atomosphere?
Thanks,
Soccersparks

At sea level, on Earth, the pressure is "1 atmosphere". Convenient - yes.

Of course if there is weird weather that might not be true. Or if you are in a pressurized room. Weather effects can shift it but not very much...a few percent in either direction. A hurricane might shift it from 1.0 atmospheres to 0.95 atmospheres).

Mostly though, it's a fairly good assumption that p = 1.0 unless you're someplace that is not at sea level. You can't say 1.00 though, because it might range from 0.96 to 1.02 or so based on weather and humidity.

Altitude matters.

Denver, for example, is 5000 feet above sea level and is about .83 atmospheres on average, according to one source I googled.

I'm sure there is a formula for that too. However it would have been best to actually take a barometer reading when you did
the experiment, to make it less of a guess and more of a known value. There are too many variables to make average pressure formulas more than guesswork. To convert whatever you've got on your barometer to atmospheres, this link can help.

http://wiki.answers.com/Q/What_is_air_p ... f_pressure

[soccersparks]

Hi,
Ok this is getting way over my head for my age.
I am thinking of making my project this:
Object: To see if putting insulating materials in between my metal spheres affects the distance of the spark.
Does this seem like it would be a good project for a 6-8 grade project? Please give me some feedback on what you think.
Thank you,
Soccersparks

[bradleyshanrock-solberg]

That question is a lot easier for your level of training because you don't have to understand the gap formulas, you just have to do careful observations and report the results.

So yes, that would be more appropriate for your grade level. It leaves algebra, ionization constants, air pressure, humidity, etc out of it except as useful background information.

What you can take away from the discussion we've had so far is you would want to control all of these variables....do the test in a room with controlled humidity and temperature (most indoor rooms with air conditioning or central heating are pretty consistent) and in the same gas (easy enough - use air, don't let anybody smoke in the room or do anything else weird that would change the composition) and don't do one test at sea level and another test in Denver Colorado.

But assuming you set up your apparatus in one room, use the same room for all experiments and preferably perform the experiments all on the same day (to mimimize any unusual pressure variations due to weather) all of that should cancel out and what you're left with is something like this.

1. measure spark gap in air
2. measure spark gap in some other gas (challenging in grades 6-8 unless your science department can put the spark balls in a bell-jar with other gasses)
3. measure spark gap where something other than air is between the two balls

For #3 you would want to consider both the material and how thick it is. Eg, a piece of paper might have less of an effect than a notebook of paper, not because the material is different but because you have more insulating materials.

[soccersparks]

Hi,
Yes this is already sounding easier! Now in this type of project where is this principle used in real life?
Thank you,
Soccersparks

[bradleyshanrock-solberg]

Actually yes. Although some of these are not really used in modern times. Just off the top of my head....

1. spark plugs in internal combustion engines. Get the gap wrong for the fuel mixure and the car goes "out of tune" - it performs badly or may even have the engine quit altogether. This is less common in fuel injection systems but a lot of vehicles in the world still use spark plugs.

2. static electricity discharge. Sometimes this is dangerous (eg, when pumping gasoline into a car) or can damage delicate electronics (when manufacturing electronics, extreme steps are taken to prevent static discharge). Anything that might be damaged by a spark of static electricity needs to be insulated

3. Wireless telegraphy used spark gap transmitters to do "morse code" transmissions without needing to be physically connected. It's the great-grandfather of modern wireless internet.

4. connectors used in high voltage machinery, transformers or transmission lines. You absolutely don't want electricity arcing from component to component, so you need to put the right kind of insulation between them. You also want the insulation to be cheap and durable.

5. electromagnetic pulse weaponry. This is a military device designed to shut down electronics. This really uses the same principle as wireless telegraphy but it's the relationship between a firecracker and a stick of dynamite. Instead of creating a magnetic pulse that can be detected by radios it creates one that destroys electronics.

[soccersparks]

Hi,
Ok great!!This is a lot of help !! Now i am having trouble finding metal spheres at a 25 mm diameter. I have tried looking for all the types of balls used in the example. Do you have any other suggestions?
Thanks,
Soccersparks

[bradleyshanrock-solberg]

That I can't help with. The only time I did electronics of this type was in college and I had the benefit of a fully equipped electronics lab and a shop in the same building that sold anything the lab didn't have. I do not know where a normal person would buy one. You might start with some place like radio shack that supports electronics enthusiasts and ask questions. Or poke around on the internet.

[Louise]

Hi,
Ok great!!This is a lot of help !! Now i am having trouble finding metal spheres at a 25 mm diameter. I have tried looking for all the types of balls used in the example. Do you have any other suggestions?
Thanks,
Soccersparks

Try a hardware store. Ask for 'ball bearings'.


Louise

[soccersparks]

Hi,
The picture on the project page for how far can sparks jump, are they inlarged by a big amount?

[soccersparks]

Hi,
In the project "how far can sparks jump" appoximately how big should the piece of cardboard shaped as a V be?
Thanks for the help,
Soccersparks

[deleted-139256]

This isn't an extremely exact answer but just eyeballing one of the V picture would lead me to believe each hinge is about 2ft by 2ft.Note that this is just based on the fact the protractor in th picture is probably somewhere 6-12 inches long(though it does look on the bigger side).Start with a larger box and cut it down to size as necessary.

Phi-unit

[soccersparks]

Hi,
I am doing the project how far can a spark jump. In my previous posts i said that i was cahnging my project slightly to the objective being if putting an insulating material in between the metal spheres. Well i have done that and i put a piece of foil in between the metal spheres and the electric current went to the top of the foil and down to the cardboard which had some clay on it from the modeling clay. Why does it do this?
Thank you,
Laine

[bradleyshanrock-solberg]

What you just witnessed is how lightning rods work. They divert current from the structure they're attached to by being a better "ground" than the structure. Electricity goes from positive charge areas to "ground", picking the easiest path it can find.

When you stick an insulator between two metal balls, it is unlikely to be a better "ground" than the other ball no matter how it is mounted. But something highly conductive like metal foil is going to be pretty attractive as long as it is connected to the ground somehow. Cardboard and modeling clay aren't great conductors but they might be better than the remaining air gap between your foil and the other metal ball (they must be if the current was diverted).

To avoid this problem, you could try suspending the foil with something like string or yarn instead of mounting it on the ground. (don't suspend it with metal wire...). Or you could try to insulate whatever you're using to mount the foil, as an example, putting a rubber mat or similar good insulator under your cardboard/clay contraption.

[soccersparks]

Hi,
In my previous post i said i was doing a simpler version of the project how far can a spark jump. I am focusing in on insulating materials. I have a little wooden box with the wires attached to the electodes. I found a consistant gap and i put materials eg. paper plastic wood metal in the gap. If the spark goes through it is not a good insulating material. Well now i am starting my board and i am drawing a diagram on how the electricity gets from inside the pizeolectric starter and the electodes. Can you please explain to me this process?
THank you,
SoCcErSpArKs

[bradleyshanrock-solberg]

Ok, you need a few basic concepts. You can look up the terms here on wikipedia, they give a pretty good explanation without going into too much mathematical detail, but here's the basic concepts.

1. Piezoelectric materials - if you squeeze them, they generate a positive electric "charge"

2. "charge" - this can be thought of as a bunch of electrons free to travel (not tightly bound to atoms)

3. "voltage" - all electric circuits have start points and end points, with electrons flowing from one point to the other. The difference in electric charge in these circuits is called "voltage". Usually, and probably in the case of your experiment, the "end point" is a reference point - the planet Earth. The circuit is physically connected to the ground, and this end is called "ground". In the case of something like a battery, the + side has a higher charge than the "-" side. If you use the battery in a flashlight or ipod or whatever, what is happening is the device is connecting the positive and negative side of the battery. Current flows between the + and - side until the battery is discharged (+ and - now have same "charge"), powering the device - generating light or activating the MPG player & flash memory in the IPOD. Flashlights are easier to explain and all the parts are in the open for you to look at, so we'll stick with that going forward. They're just a wire going to the lightbulb, connected to + side of battery, and a wire on the other side of the lightbulb going to the "-" side of the battery.

4. "resistance" - if the electrons could move just the way they wanted to, there would be no resistance on the way from positive to ground, or positive to negative charge. In reality, even good conducting materials like copper will resist the flow a little. In most materials this is expressed as heat. A flashlight shows this in a pretty obvious way - the filament in the lightbulb generates light yes, but it also generates heat. The conversion of electric power to light is accompanied by some waste. If the batteries are almost discharged, the light is faint, and then eventually winks out. It takes a certain amount of voltage to activate the filament, to make light. The more distance the electricity must travel in a given material, the more overall resistance to the flow. So a really long copper wire will heat up more than a really short one, with the same voltage and current. (this is why appliances that use a lot of power tend to have short power cables and you're not supposed to string multiple extension cords together unless they're rated for it - the heat can actually cause fires)

5. spark gap - air has a certain resistance. If the voltage is sufficient to exceed the resistance of the air between the positive and ground or negative charged end of the circuit, you get a spark. If not, you don't get a spark.

Moving on to your project, what is going on is quite similar to a flashlight, except that instead of a filament that lights up, you have an air-gap that causes a spark. The sequence is like this

A. Squeeze the piezoelectric material, generating a positive charge (greater than whatever is on the other end of the spark gap, probably "ground"

B. There is now a voltage potential between the two ends of the circuit. Electrons want to flow from one end to the other. With nothing inbetween, it "sparks". (you set it up so this would happen, this is the control case)

C. If whatever you position inside the gap is at least as conductive as air, you'll still get a spark. If it is less conductive but the combination of air gap resistance and this material doesn't exceed your voltage potential you will still get a spark. If it adds sufficient resistance to prevent the spark, you are calling it an "insulating" material.

D. An "insulating" material might not prevent the spark if other conditions of your experiment change. If you generate a bigger charge (perhaps by squeezing the Piezoelectric material with more force) it might spark. If you reduce the air gap (move the ends closer together) it might spark. If you reduce the thickness of the insulating material it might spark.

(note - try to have the thickness of the insulating material the same, or at least report how thick it is. Plastic wrap and a 1" thick piece of wood can't be directly compared with respect to how resistant their material composition is, but you could comment on whether either has an insulating effect. A lot depends on how you present the experiment. If it is something like "do common household materials work as insulators" then thickness is less important than using it in the form you find it. If you're trying to say "is wood a better insulator than plastic wrap" you need the thicknesses to be the same)

Hope that helps some.