Super Charge A Basic Magnet Science Fair Project

Magnet or electromagnet? To what is the power connected?

Just a reminder: To avoid or prevent anybody from getting hurt due to electrical shock. Be sure Not to touch any bare wire connections, making or breaking any connections while power source is ON or while circuit is energized. Depending on the number of turns used in the coil, there will be a much higher back EMF due to the inductive load (coil)!

I wouldn't think there would be a safety issue there due to the low voltage and small inductance involved (unless they get really ambitious with the coil size).

The biggest safety issue (not including wire heating) is the mains voltage powering the power supply.

Safety issues can appear from almost anywhere and when you least expect them. At work I have a project where the two electromagnet coils are powered by just one ±10VDC supply for each coil. These supplies each produce 75 amperes of current. One of the bolt and nut pairs in the low voltage power cabling loosened from the thermal cycling and welded themselves together at the transition into the vacuum chamber. It was later found out that the overworked mechanical assembler ran out of readily available lock washers.

Lack of knowledge, experience or plain ignorance on the subject matter are good components of an accident waiting to happen! The young girl may accidentally get hurt from an accidental electrical discharge derived from Ldi/dt. Sine the OP nor anybody knows for sure how long, or what the cross-sectional area of the magnet wire used in the experiment, how would you know what the maximum current is going to be in that simple circuit?

It's all about risk assessment and analysis. You can accidentally kill yourself with an average everyday 9V DC battery, but the chances are so remote that I didn't mention this point.

Lets not go TOO overboard with the safety warnings, this is after all a school science fair project (very likely a home made coil wrapped on a toilet roll or nail or something) not someone asking a question on how to design a building distribution board or substation (where are your safety warnings for them!).

Life is about some level of risk (even if it is only very, very small), so lets not wrap our children in cotton wool too tightly least they miss out on experiencing it.

_{Jack - No I am not going to tell you how you kill someone with a 9V battery.}

Risk, no matter how remote or minute is still a Risk! The same risk associated to what is known as micro-shocks as it relate to heart causing fibrillation or even death!

Besides, the word of caution I posted was intended for the OP and his daughter, as well as for those who can relate to it! It is not at all meant for you who seems quite knowledgeable, yet failed to consider "Murphy's Law"!

Point taken and your warning in post #21 is quite clear on the subject.

'...._{Jack - No I am not going to tell you how you kill someone with a 9V battery}.....'

...because the information is so readily available.

What, if I may ask, are you attempting to demonstrate?

You can increase the power of the magnet by increasing the number of coils, making sure that the coils are wrapped in succession and evenly spaced....also by using a softer iron rod....

http://catalog.miniscience.com/Catalog/Metals/Iron.html

http://www.magnetics.com/product.asp?ProductID=138

Here's some cool ideas for projects using magnetism....

http://chemistry.about.com/od/sciencefairprojectideas/a/magnetprojects.htm

That's what I'm talkin about...

Hi SolarEagle:

Using your pic of the two batteries, switch and the electromagnet, and the current flowing from pos to neg what would the north and south poles of the electromagnet be labelled on the nail? I have forgotten the convention. Can this be figured out using the LH rule?

Thanks

UFG

"...and the current flowing from pos to neg..." & "Can this be figured out using the LH rule?"

O N L Y ... IF you FIRST decide whether (with regard to "current") you are talking about "Hole_Flow" or "Electron_Flow"...

The "Right Hand Rule (of thumb)" depicts the orientation of magnetic lines of field around a conductor when the thumb (of the "gripping" hand) points in the direction of electron flow.

The "Left Hand Rule (of thumb)" achieves the same depiction if the thumb is pointing in the direction of Hole flow.

Lest we lead anyone astray, do not forget that the more electronegative end of a battery (the negative terminal) is the one possessing an excess (preponderance) of electrons. Thus, when a circuit is completed (across a battery) the electrons are what flow from the negative terminal, thru the circuit, and back-into the positive terminal.

(( Hook up a simple nail-wire-battery, and point the end of the nail at a compass needle to determine which end of the nail is N-vs-S...))

Yes ndt has answered correctly, here's a little primer to see this in graphic....

http://www.electronics-tutorials.ws/electromagnetism/electromagnetism.html

http://tymkrs.tumblr.com/post/5513058883/conventional-flow-vs-electron-flow-theory

I am assuming that MattJ's Post#8 (Replying-To #5) was ALSO replying-to your query in #4...(which deserved/deserves answer).

I like the 1st link ("tutorial") you posted in #22 above... VERY appropriate *pointer* (assuming that this is an "Elementary / Middle-School / Jr. High" assignment). (our company's filter, for some reason, won't allow the 2nd link to be shown)

For anyone in High School or beyond, some additional research / education ("heavy-duty-insight") ought to be gained in the course of such a project.

Though I'll readily admit that the math is over *my* head, I feel as though some of the "beauty" (of the "insights" afforded) comes-through by reading about Maxwell's incredible clairvoyance on the subject.

Pg 4, the next-to-last paragraph, of Professor Dyson's essay-paper (Princeton):
Why is Maxwell's Theory so hard to understand? really drives home (to me, anyway) the "abstraction" of electro-magnetic fields....indicating how much we have yet-to-learn.

FYI....

"

Conventional Flow vs Electron Flow Theory

So in working on my foxhole radio - I realized I needed to look at diodes a bit more as I was making essentially a DIY diode with the pencil and razor blade. And in looking at diodes, I realized that something just didn't add up. And perhaps by the end of this post still won't add up.

I'm going to further preface this by saying I think having two different theories is dumb and stupid. Especially when people are trying to learn this stuff for the first time!

So video below shows what I understand:

http://youtu.be/tQlijFJMw_g?hd=1

The question is if current/electrons go from the negative side of the battery to the positive side of the battery, how do diodes only allow current to go from anode to cathode (or P to N)?

Alright, so after digging around /way/ too much, it seems that there are TWO different types of theories - the right one and the wrong one that people keep around because it's been around for a long time. I seem to be referencing both with my question. Let's start with the wrong one:

Conventional Flow Theory

The idea was that charge flowed from something with positive charge to something with negative charge (though negative charge is due to having more electrons). And because we associate "positive" with "surplus" and "negative" with "deficiency," engineers decided to retain the old concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly.

Electron Flow Theory

This is clearly not how batteries work. So another theory called the Electron Flow Theory came about to show how electrons actually moved - which was from negative to positive (as the electrons moved from the negative to the positive pole):

Diodes

Ahh…much better. But then we have the diode issue - below is what we would expect of a normal diode set up:

So when the + end of the battery is attached to the anode, and the - end of the battery is connected to the cathode, we get current capable of lighting up a bulb!

If we label this according to conventional flow notation - everything makes sense - current goes from the surplus side to the deficient side of things and current goes through the diode as expected.

But! If we use electron flow notation - the way electrons actually "move" around in a circuit we get the following. And it looks completely backwards to how we'd expect current to move in a circuit with a diode:

How has it been explained away?

So some people say, just deal with it or that's just how people notate it. But if the electron theory shows current flowing in the very direction that a diode's supposed to block it, how can /anyone/ ignore it?! And with almost everything else we talk about where/how the electrons move through a component…but somehow the definition of a current changes for diodes? *confused* Here are some explanations others have given:

• In a semiconductor it is sometimes useful to think of the current as due to the flow of positive "holes" (the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron).
• In semiconductors, when we say current flows from + to -, we don't mean the electron flow, we mean the hole flow. We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a "hole" of positive charge that originates from the proton in the nucleus which no longer has its charge canceled to zero because the electron isn't there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current. So it's hole flow for entire circuits and not electron flow?
• Current is positive charge. So even if protons don't move, the fact that electrons are moving from the negative to positive end of a diode means that a positive charge is "moving" from the positive to negative end of a diode.
• The latest explanation is that direction is less important than how they are placed in the circuit - that is relative to the polarity of the power source. So if they are placed in a configuration that allows current flow through them, so be it. But if the polarity reverses, it'll block current. So if you have an ac current, it will seem as if the diode is blocking current from one "direction" but not the other. Thanks to @whixr for his help :p

@atdiy/@tymkrs

1. http://www.opamp-electronics.com/tutorials/conventional_versus_electron_flow_1_01_07.htm
2. http://mste.illinois.edu/murphy/HoleFlow/HoleFlow.html
3. http://www.electro-tech-online.com/general-electronics-chat/90846-help-conventional-flow-vs-electron-flow.html
4. http://www.allaboutcircuits.com/vol_3/chpt_3/1.html

Maybe. There's not enough information to even make a guess what you are doing here. How much power can each supply provide? Are you making an electromagnet with these supplies? If you are what is the resistance of the electromagnet? Are the supplies AC or DC?

That's four questions. I'll let others ask the remaining sixteen.

Just taking the + wrapping it around an iron coil and then going back to the -. 24vdc ps. Electromagnet

OK. With increased voltage comes increased current and increased heating, as others above have correctly pointed out. While a little trial-and-error can be a valuable learning exercise, do be aware that there are risks with things getting hot and melting that need to be examined in a safe environment. One hopes that the power supply has overload protection or a current-limiting feature, and some sort of variable voltage facility so that it can be turned down if things start to glow or start to emit smoke.

Safety overglasses perhaps? Adequate ventilation? Flammable materials all absent? Cat in another room?

Actually, cancel the cat suggestion; they are supposed to have nine lives....

Eh whaaa?
Sorry, didn't hear... I was in the other room.

You'll prob fine you need an awfull lot of wire, or nasty large currents, but Idunno..that's the fon of experimenting. Get hold of an old 24v relay or solenoid too, in case the home brew electromagnet doesn't work.
Del

Go for it. Try different numbers of turns of wire, different numbers and sizes of iron cores. It is great fun.

That is the way to learn.

Skim through http://en.wikipedia.org/wiki/Electromagnetism

Just remember that 24v can create big sparks and get your daughter to wear eye protection.

I remeber a battery manufacturer ( I think it was Ever Ready) as a stunt had an electro magnet pick up a small car powered by only a single "D" cell (1.5V)

It took some careful magnet design and was a rather extreme example.

Lots of turns of wire is the trick ;)

Thi ssite has some cool electro magnet experiements

http://www.coolmagnetman.com/magelect.htm

The safest way to go is to increase the number of turns. A 9v battery has a fair amount of internal resistance (more than your coil, probably) that limits the current. Most of the heating is in the battery. Unless your power supply has a current limit, its internal resistance is low and I would say it is a bad idea to connect it directly across the coil.

Your magnetic field is proportional to the current times the number of turns. A 9v battery can only deliver a small amount of current. Try using a D cell. Even though the open circuit voltage is lower, it will deliver a larger amount of current. Use a push button switch and only switch on for a short time until you see that your coil can handle the current.

Don't touch the wires. Two reasons - they may get hot and when you switch off, there may be a voltage pulse due to the inductance in the circuit.