Ampere experiment. - Page 1
Forum section: electronics / beginners

author: NickPerry
author_rank: Contributor
timestamp: October 21, 2016, 08:46:58 pm
content: Ok, I'm trying to find an example of an actual way to measure 1 amp (NOT using a pre-known measurement tool like a multi meter)according to Wikipedia the procedure goes as follows:-get 2 infinity long wires.-Place them in a vacuum.-space them 1 meter apart.-attach a scale to them to measure how much attraction force they exert.-pass a current through both of them (same current, in the same direction, so I guess hook the 2 wires up in series?)adjust the current until the scale reads 2 x 10 ^ 7 Newton meters of force. (no clue where they got this number, if you know please let me know)now you have the baseline of 1 amp, and can continue to count the electrons to get a coulomb, and calculate out what 1 volt/ohm/watt is.but I can't seem to find anywhere where they do this experiment (lots of people making electromagnets, but no one figuring out the actual ampere's running through the system using that magnetic attraction)any thoughts on this?

author: TimFox
author_rank: Super Contributor
timestamp: October 21, 2016, 08:53:24 pm
content: In practice, this is done by winding two coils with accurate dimensions and calculating the force per ampere between them using your equation and the integral calculus.These two coils are then used in a balance, similar to a weighing scale, comparing the force between the stationary and dangling coil with the gravitational force on the usual masses on the other side of the beam.Seehttp://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Current_Balance/Current_Balance.html

author: NickPerry
author_rank: Contributor
timestamp: October 21, 2016, 08:57:35 pm
content: so basically a watt balance in reverse?makes sense, though I'm not sure how one converts an infinity long wire to that of a finite length coil. but I guess that's why we have mathematicians.

author: Rerouter
author_rank: Super Contributor
timestamp: October 21, 2016, 09:02:52 pm
content: the wires can be any length, what you will be measuring is the repelling force of the magnetic field that current generates,Here is what you are currently using for the mathhttp://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.htmlWhile you should probably be using force per unit length as per herehttp://theory.uwinnipeg.ca/physics/mag/node10.htmlThis effect can be measured even centimeters apart, just the closer they are the easier it is to see,I would not have through a vacuum to be necessary, just still air,and its 2x10^-7 Newtons of force produced by 1A flowing through long wires spaced 1m apart,still, if you get them much closer that force increases, but there is a golilocks zone where your wire diameter appears small compared to the spacing, and the spacing small to the wire lengthhttps://en.wikipedia.org/wiki/Amp%C3%A8re%27s_force_law

author: NickPerry
author_rank: Contributor
timestamp: October 21, 2016, 09:06:28 pm
content: Thank you!that's some very useful information!Time to crunch some numbers & build an experiment ^.^Thanks again!

author: Brumby
author_rank: Unknown
timestamp: October 22, 2016, 02:10:52 am
content: Quote from: NickPerry on October 21, 2016, 08:57:35 pmMathematicians handle infinitely long wires as easily as EEs can handle a soldering iron.Being capable in both is fun.

author: IanB
author_rank: Super Contributor
timestamp: October 22, 2016, 02:31:50 am
content: In case it is ambiguous, the force between parallel wires is theforce per unit length. The total force between a pair of infinitely long wires would of course be infinite...The reason for saying the wires should be "infinitely" long is to ensure a uniform magnetic field and avoid any end effects where the magnetic field becomes distorted.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 22, 2016, 06:42:32 am
content: Quote from: IanB on October 22, 2016, 02:31:50 amOf course,if they are infinitely long,they may traverse regions which cause such distortion of the magnetic field.No matter,they are in "free space".In very early times,one alternative specification was how much mass of metal a current could deposit in a given time,in an electroplating bath.