Force in coil

[bro]

Hi,

 

a Q: if I put a ferromagnetic material inside a coil

with current and magnetic field, will the material

be accelerated along the coil - like it would be

attracted to a magnet pole ?

 

thank you

[aommaster]

From what I can remember, no, it won't. This is because the magnetic field is travelling on the outside of the coil and not the inside. However, the metal the you put in would become magnetised, and in effect, you would have made an electromagnet.

[YT2095]

Hi' date='

 

a Q: if I put a ferromagnetic material inside a coil

with current and magnetic field, will the material

be accelerated along the coil - like it would be

attracted to a magnet pole ?

 

thank you[/quote']Yes, it most certainly will, that is the entire principal behind an electomagnetic Sollenoid

[aommaster]

so, what i said was incorrect?

[YT2095]

not exactly incorrect, it would indeed become an electromagnet, but on doing so and allowed to move, it would indeed try to "centralise" itself and ballance out the EM field, and it wasn`t, then it would move the insert

[aommaster]

Oh ok !

[bro]

thank you YT2095.

 

Intresting, so how come there are no coil-guns out

there and many railguns ? How would you go about

calculating the energy of the magnetic flux and

how it's transferred to an accelerating feorromagnet

piece ?

 

thank you.

[swansont]

so, what i said was incorrect?

 

An ideal solenoid has no field outside of it, so that part of it was incorrect, and thus anything derived from that notion is incorrect. Of course, a real (i.e. non-infinite) solenoid will have a field outside, since the divergence of B is zero - but the field is much stronger inside.

[Lance]

thank you YT2095.

 

Intresting' date=' so how come there are no coil-guns out

there and many railguns ?

 

[/quote']

 

When is the last time you saw a rail gun that did more than shoot plasma? Coilguns are out there. You are just not looking in the right places.

[bro]

When is the last time you saw a rail gun that did more than shoot plasma? Coilguns are out there. You are just not looking in the right places.

What do you mean ?

As I see it here, if I put a metal piece on a surface and put a

high current coil around it - I understand that the piece will

go flying through and out of the coil along the field lines ?

[BPHgravity]

Coil guns are actually quite common and easy to make. Many electrical engineering schools or electrical apprenticeship facilities have played with the concept.

 

A coil essentially takes on the properties of a bar magnet when a current is passed through it. A North and South pole can be determined by current direction. If a magnetic material is placed near the energized coil, it will be attracted to the coil, if the direction of current is switched at the appropriately calculated time, the coil will repel the material and shoot it out the other end.

[YT2095]

^^^^^ Yup, what he said ) ^^^^^^

[bro]

Coil guns are actually quite common and easy to make. Many electrical engineering schools or electrical apprenticeship facilities have played with the concept.

 

A coil essentially takes on the properties of a bar magnet when a current is passed through it. A North and South pole can be determined by current direction. If a magnetic material is placed near the energized coil' date=' it will be attracted to the coil, if the direction of current is switched at the appropriately calculated time, the coil will repel the material and shoot it out the other end. [/quote']

Hm... O.K. I've heard of these things shooting

nails and stuff. But that's not wjat I'm asking cause

that's an AC device and as I understand it - it induces

a field and then pushes against it with a reverse field

using AC.

 

I'm asking about a DC coil with a constant field. Say you

make one of those magnet experiments with the metal

particles and there's no resistence, they shouldn't just form

a field lines pattern, they should move to one of the poles, right ?

Same thing as I'm asking, I believe, put it in a field of say a long

DC coil and it will keep accelerating through it all, or not ?

 

thanx

[Lance]

No it will stay in one position. But if you tap it on/off it will have the same effect as a coil gun.

[bro]

So, what's the difference ? A permanent magnet would

attract that metal piece, but the coil's field wouldn't ?

 

thanx

[Lance]

Yes of course it would but as soon as the metal got to the center of the coil it would stop moving.

[bro]

So, it's a matter of increasing magnetic flux ?

[YT2095]

no, it`s a mater of switching the coil off as soon as it reaches the center, the momentum of the moving metal will allow it to continue forwards as the coil is now off and there`s no magnetic feild to pull it back

 

the easiest way would be a break beam light sensor, as soon as the metal is half way into the coil it breaks the light beam and turns the coil off

[bro]

O.K. but the field is still in the same direction, so what

changes is only the flux, right ? So, say, in an infinite coil

it wouldn't move when it's already in, despite the H field ?

[YT2095]

the coil will atract the metal when ON, and will stop when OFF. if you carefully time this you can acheive linear motion of the metal.

the metal starts off stationary, gets velocity 1 as it reaches the middle of coil 1 the power is turned off in that coil and coil #2 powers up, but since the metal already has some speed it will exit coil 2 faster than it did at coil #1.

do this over a whole series of coils and you`ll get some pretty descent speed out of your metal!

I made a small one many years ago out of 2 old Betamax video recorders, they have all the parts you need for a 4 coil gun, even the break beam sensors, switching transistors, and power supply, all you have to do is drill the end stops in the 4 solenoids so that you metal rod will slide right through. with only 4 coils I could eject the metal slug a good 2 meters!

[Lance]

I did It with disposible cameras I got for free, Most photo development places will give them away Although I still had to go to radio shack for some parts.

[YT2095]

did you use factory wound atractor coils or homemade? I find the factory made ones much better, it seems that no matter how carefully I wind, I can never seem to match the same standard

secondly, I don`t know if you`re aware of this, but the cam flash chargers can be modified to charge more than one cap in parallel, the charge time is increased sure, but you double the coulombs out

I`ve lit 60w 240v bulbs with 2 AA bateries in the past, it stays lit for a good half second! before a recharge, using that on a few ohm coil would give a hell of a descent EM pulse!

[Guest Lester Ani Ben]

Ok, i heard the EM pulse. I know what an emp is, and what it does, but can you tell me how to make one? I would just love to power down something nearby.

[swansont]

Speaking of coils, I wound one recently and am getting set to measure the field uniformity.

[YT2095]

Swansont: Sweet looking coil! what`s it for? it looks a but like a Tesla Secondary.

 

as for making an EMP of appreciable strength, you`ll need large capacitors, a suitable charger, a damped sparkgap and trigger, and also a tank coil (use copper tubing, never a solid).

some insurance would be a good idea too