Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85
If anyone could provide insight as to how to find the force (in newtons or something that we can get to newtons with) of an electromagnetic with known properties? I have done an experiment and would like to compare experimental values with theoretical ones, but the only equations I can find are for magnetic force, and I don't think that's the same thing.

Any help or places to look for help in the next six or so hours would be greatly, greatly appreciated.
mtb0minime
minimember
+2,418|7135

Could you be a little more specific? What values do you have? Try wikipedia, it helped me through my electricity and magnetism lab last summer. I've still kept my physics book to this day, so if you give some specifics and givens, I'll try and look some stuff up.
ThaReaper
Banned
+410|7120
There's always this
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85

mtb0minime wrote:

Could you be a little more specific? What values do you have? Try wikipedia, it helped me through my electricity and magnetism lab last summer. I've still kept my physics book to this day, so if you give some specifics and givens, I'll try and look some stuff up.
One of my tests showed with .8 amps run through the electromagnet held 382g. (.382 * 9.8 for force)

Electromagnet is 6 inches long, about 1020 wrappings.

Tried wikipedia and have a physics book (granted, that is beyond me, but I still think I'm finding all the equations it gives on the subject), but really the only one I can find is:

B = ((permeability of free space) (amperage) (number of turns))/unit length of solenoid

Where B is magnetic force. I can't go from magnetic force to something I can compare to how much it can hold, so it doesn't do me much good.

ThaReaper wrote:

There's always this
Dude, seriously, don't screw with me when I am deperately trying to work on equations that are beyond my comfort level. I have tried Google damnit, unless you can prove me otherwise it does not help. A bullshit response like that might make me flip out and ban you in my present state of mind.
ThaReaper
Banned
+410|7120
Is this for college or something?
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85
No, it's not, it's for science fair. I'm in 11th grade, taking a very noob physics course, so I need some help with equations I don't know.
ThaReaper
Banned
+410|7120
I thought you were older... Dang. I'll help you out though.
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

Hmmm...

Asian in AP Physics to the rescue!

First off, what do you mean by "the force of an electromagnet"?
https://i.imgur.com/PfIpcdn.gif
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85

cowami wrote:

Hmmm...

Asian in AP Physics to the rescue!

First off, what do you mean by "the force of an electromagnet"?
I mean I need to compare the amperage run through an electromagnet to the amount of stuff it can hold up, so that the force of the electromagnet exerted on the object is the same as the force exerted by the earth.
CommieChipmunk
Member
+488|7050|Portland, OR, USA
Isef?
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85

CommieChipmunk wrote:

Isef?
aye
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

In other words:

F = IBL
Where F = force
I = current (amperage)
B = Magnetic flux density (Teslas)
L = length

Set that equal to F=mg (which you should know by heart), and you should get your answer. (Or something along those lines)
https://i.imgur.com/PfIpcdn.gif
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85

cowami wrote:

In other words:

F = IBL
Where F = force
I = current (amperage)
B = Magnetic flux density (Teslas)
L = length

Set that equal to F=mg (which you should know by heart), and you should get your answer. (Or something along those lines)
L is the length of the electromagnet in meters yes?

If this comes out right I will make sweet man sex to you. I couldn't find F = IBL anywhere, thank you.
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

Flaming_Maniac wrote:

cowami wrote:

In other words:

F = IBL
Where F = force
I = current (amperage)
B = Magnetic flux density (Teslas)
L = length

Set that equal to F=mg (which you should know by heart), and you should get your answer. (Or something along those lines)
L is the length of the electromagnet in meters yes?

If this comes out right I will make sweet man sex to you. I couldn't find F = IBL anywhere, thank you.
Aye sir.

F = BIL is the equation for the "back EMF" of a rod/coil/length of wire moving through a magnetic field. Essentially, it's the resistance faced by said segment of wire.

EDIT: Good timing on this too, I'm studying for my test tomorrow. D:

EDIT 2: I lied. F= BIL is in fact, better known as F= ILBsin(theta), which gives you the force on a current carrying wire. Not that it really matters, but just so that it doesn't confuse you.

Last edited by cowami (2008-03-11 20:08:00)

https://i.imgur.com/PfIpcdn.gif
bf2gammer
Member
+14|6701

ThaReaper wrote:

There's always this
did i just see you post that bullshit on a moderators thread? wow you got balls. "sorry for the spam, i had to say something"

Last edited by bf2gammer (2008-03-11 20:01:23)

Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85
I'm getting like 170,000% error.

One of my trials was 2.2 amps held 1132g. I did:

(4pi*10-7 * 1020 * 2.2) /.1524 meters = B

F = B(2.2)(.1524m) (comes out to about .0059)

F = 1.132kg(9.8m/s2) (comes out to about 10.06 )
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

hmmm
https://i.imgur.com/PfIpcdn.gif
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85
I wouldn't exactly expect my experiment to be that good, but I thought it would be better than that, and the real problem is I saw more force being exhibited than I get in the calculations. If it was the other way around I would be more inclined to believe I didn't screw something up.
mtb0minime
minimember
+2,418|7135

Wait a sec, the L in that equation isn't the length of the magnet, it's the length of the wire. I imagine you've got wire wrapped in a coil or something?

There's also an equation for torque:
T = NIAB sin (theta). N: # of turns/wraps, I: current, A: area of loop (pi*r^2 if it's circular), B: magnetic force, angle theta is angle of loop with respect to magnetic field.

Hmm, but now that I think of it, if you use this, sin theta = 0, so that's not much help.


Oh here we go: Apmere's Law for a Solenoid (wrapped coil of wire); B = u0NI / l
That should be the one you use.
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

Was this solenoid circular? If it was, there might be another equation we can try.

EDIT: Matt, that's what he used, but it still didn't work out. Perhaps something's wrong on my end...

Last edited by cowami (2008-03-11 20:17:34)

https://i.imgur.com/PfIpcdn.gif
bf2gammer
Member
+14|6701
F = B(2.2)(.1524m) (comes out to about .0059) i got about .062037 "not sure if that is accurate" try that? otherwise i have no idea
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85
Yeah, not sure about how to use the torque one. My experiment has completely linear vectors...but maybe I'm just a noob.

I was using Ampere's second law, but that just gets me B, which I think is in teslas, not newtons.

I just used L in the F = ILB equation, and I came out to about 1.something. So much better, still in the wrong direction, but only about 900% error.
cowami
OY, BITCHTITS!
+1,106|6770|Noo Yawk, Noo Yawk

Flaming_Maniac wrote:

Yeah, not sure about how to use the torque one. My experiment has completely linear vectors...but maybe I'm just a noob.

I was using Ampere's second law, but that just gets me B, which I think is in teslas, not newtons.

I just used L in the F = ILB equation, and I came out to about 1.something. So much better, still in the wrong direction, but only about 900% error.
Well, just in case you had it at an angle...

The full equation is:
F = ILBsinθ



EDIT: In case you CAN use torque:

τ = Frsinθ

Last edited by cowami (2008-03-11 20:28:39)

https://i.imgur.com/PfIpcdn.gif
mtb0minime
minimember
+2,418|7135

Arg this is complicated hah! I save all my notes and my physics professor was amazing and I really understood the stuff back when I took the class.... but my notes are at home

I'll keep looking though. Physics for fun >> geotech engineering hw.
Flaming_Maniac
prince of insufficient light
+2,490|7187|67.222.138.85

cowami wrote:

Flaming_Maniac wrote:

Yeah, not sure about how to use the torque one. My experiment has completely linear vectors...but maybe I'm just a noob.

I was using Ampere's second law, but that just gets me B, which I think is in teslas, not newtons.

I just used L in the F = ILB equation, and I came out to about 1.something. So much better, still in the wrong direction, but only about 900% error.
Well, just in case you had it at an angle...

The full equation is:
F = ILBsinθ

No angle, but good to know.

mtb thanks for all the help, don't let your geo homework suffer too much.

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