Science Buddies: "Ask an Expert"

soccersparks wrote: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

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

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.

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

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.

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

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.

soccersparks wrote: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

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

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

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

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

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.

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

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.

Ok thank you i think i got it. One other question though. What is in the palstic or any of the good insulating materials that makes the spark not go through it?
Thank you,
Soccersparks

There are whole college courses on that topic, but lets see if I can get a few key concepts across.

There are three rough categories of materials. How they behave with electricity depends on the atomic structures. Atoms are made of protons and neutrons in the core or nucleus, plus electrons which kind of orbit around the nucleus. It is sort of like the solar system, with planets rotating around the sun...electrons would be the planets. (it's not a perfect match in concepts, electrons are more like a cloud around the center than solid objects going around in predictable orbit, but the basic idea is useful for thinking about it.

Conductors - most metals, for example. These materials have electrons that are weakly bonded to the atom as a whole....they can be "stolen" by another atom (or used kind of as glue to hold two atoms together, shared by both. They can also just move away completely when there are charge differences attracting elecrons in a direction. The concept is called "mobile charges". The atomic structure doesn't resist motion of electrons, at least not much.

Insulators - plastic, wood, air and most porous substances like styrofoam that have air in them. These materials have electrons that are more tightly bonded ("no mobile charges"). It's tough to get the electrons to move away from the basic crystal structure. Attempts to get them to move will just result in waste energy - heat, rather than electric current.

There is also a category of materials called semiconductors - at useful amounts of charge for the kinds of things built at human scale, these will sometimes be conductors, sometimes insulators. This switching behavior is very valuable in computers, which at the core are based on simple "on" and "off" operations, where "on" might be "current can flow" and "off" might be "current can't flow", switchable by small changes in electric current.

The distinction is arbitrary, as "Strong" or "weak" attraction depends on how big the charge difference is. Put a big enough charge on and any material will conduct electricity. On the flipside, even the best conductors have a bit of resistance and lose some energy as heat (and won't transmit very small charge differences).

In the end though, the weaker the electrons are attached to the atomic structure of the material (many materials have multiple components in them, so it's the structure as a whole that matters, not just the individual atoms in isolation), the better a conductor it is. Your insulators "hold onto" their electrons better than the air does. That's the best I can explain it without you taking courses in chemistry and physics that are at minimum high school level and likely college level. The math behind it is especially awful, especially down at the atomic level but the basic concepts that result from all that science aren't that hard to understand.

People figured this out by experiment, just like you're doing. They learned about the atomic attractions indirectly, long before they had tools to see what's going on at that level. Even now, the structures are so small that you can't really look at an individual electron. You can see atomic level structures, but not the components of atoms. (at those sizes, "looking" means either bouncing photons off things (reflection) or having them pass through things (like light through a window, or an X-ray)....and the photons have enough energy to knock the subatomic particles around...looking changes what you are looking at)

The equation you started with is an approximation used by engineers and physicists that maybe dealing with pressure vessels or high altituded so it provides a crude adjustment for special pressure conditions that you probably don't require.

At sea level, the median atmospheric pressure of 30 millibars is defined to be 1 atmosphere. Anyplace where you measure the pressure at 30 millibars, you have 1 standard atmosphere of pressure!

The humidity will have far more effect on the validity of this approximation than any atmospheric pressure differences for most places on the surface of the earth so just use "1".

Hi,
I have a question. Are hollow objects good insulating materials? If so, why?
Thanks,
Laine

A hollow object is a good insulator if it is made of something not very conductive but less conductive than air (or whatever is inside the object). If the material inside the object is nonconductive, the charge has to travel around the outside of the object instead of through the middle, so it has farther to go. Air is pretty good at insulating and a vacuum is excellent (no atoms means no free electrons to carry a charge)

The overall resistance of a circuit depends not only on the materials, but the distance involved. Hollow objects introduce greater distances. But if it is a hollow copper jar, it's still going to conduct well. A hollow plastic one will take more charge than a solid one of the same geometry to conduct electricity (and given the low melting points of plastic, it might melt from resistance heat before it conducts charge)

(and given the low melting points of plastic, it might melt from resistance heat before it conducts charge)

Excuse me but resistance heating affects require current flow (The power producing heat is proportional to the current squared times the resistance).

Hollow objects in an Electric Field are very complex things to analyze and the geometry of the field and the object and how they interact can be extremely challenging. If you are really interested in getting an appreciation for the analysis involved, look up "dielectric" properties. The simple explainations start with a parallel plate capacitor where the charge density is uniform. If you alter the shape so there are sharp points like lightning rods, the charge density is concentrated which makes the dielectric field to be concentrated and more easily broken down. The geometry of each boundary between different materials has a dielectric field and charge density distribution associated with it. This makes things like thin non-conductive tubing perpendicular to an electric field a really complex problem to figure out if the breakdown or leakage will occur on the surface or by penetrating the surfaces or if the breakdown will occur independent of the object entirely by bypassing it.

Right, Craig. You need current for heat. But you also need a medium to conduct the electricity for more than a brief period of time. (same principle as a fuse...if you overload it, the conductive surface is destroyed, usually by melting, which breaks the circuit).

If the plastic melts when the current finally overcomes the insulating properties of the plastic, the circuit won't exist very long. However it's a good point. If voltage is very high but current is low, plastic could conduct without melting, at least for a while. Voltage and current aren't the same - one causes the circuit to happen at all, the other is what generates power (or causes injury/damage). To use a hydraulic analogy, voltage might be the water pressure, but current is how much water moves through the pipes. A person can be exposed to enough voltage to create a large spark, but if current is low you will barely feel it. Relatively low voltages, that won't spark across much of a gap, can kill if the current is large. (when electricity grounds through a person, your tissues are the conductive medium. It has a resistance, which will generate heat. If heat is high enough, your tissues will burn, internal or external. Plus there is also the fact that electricity can interfere with things like the signals from your brain to other parts of the body, including the heart. It takes a lot less electricity to cause a heart attack than to cause serious injury by the burns)

And yes, current in hollow is very challenging to predict with any accuracy.

Hello Science Buddies,
You guys have been such a big help on my last project and now i have another one.
The topic is Asteroids Comets and Meteors. I am missing information and having trouble finding it. I need to know what the differences and Similarities are between them?
Thank you for all of you help!
Soccersparks

Soccersparks,

There's quite a bit of info if you google "asteroids comets meteors" -- these looked like some of the best results:

http://www.ioncmaste.ca/homepage/resour ... f_CMA.html# (click the link to "Intro to Comets, Meteors and Asteroids Movie" -- it won't let me link directly)
http://discovermagazine.com/topics/spac ... ids-comets (recent research related to them)
http://curious.astro.cornell.edu/comets.php (looks like it describes the differences)
http://www.ioncmaste.ca/homepage/resour ... dule5.html
http://www.adlerplanetarium.org/cyberspace/cma/

What kind of project are you thinking of doing? Are you interested in looking at photos taken by telescopes, analyzing data about when they are observed, examining objects that have fallen to the ground...?

Good luck and hope that helps,
Amanda