# I The functional form for dependence of force on Current?

1. Apr 13, 2017

### alfab

I am working on a lab where we were measuring how magnetic force between two parallel conductors varies with current and the separation between the two conductors. I need to find a formula for the dependence of Force on current to create a fit line on the data in my graph that shows the relation between them. I know the general equation is F=BLIsin(theta) but I remember my professor telling us that the relationship is not linear. I am not sure where to go from here or what I am missing. Is there a part of the relationship that I am missing?

2. Apr 14, 2017

### sophiecentaur

Did he give you a reference about the nonlinearity or the special conditions where linearity fails?

3. Apr 14, 2017

### ZapperZ

Staff Emeritus
First of all, you need to figure out if that sin θ factor is still needed for two parallel wires.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html

Secondly, you need to express "B" in terms of the current. Do they both carry the same current, or different?

Finally, in reference to the "not linear" part. You are being asked to look at two different dependence: distance between the two, and the current. If you have expressed "B" in terms of the current, you'll also see a a dependence on the current and on the distance between the two. It should be obvious which relationship is nonlinear. You may have both relationships being nonlinear if the current is identical in both wires.

Zz.

4. Apr 14, 2017

### pixel

Also, the referenced equation is for two "infinitely long" straight wires. You might need to assure yourself that your wires are long enough for the equation to be valid.

5. Apr 14, 2017

### alfab

Okay that link actually helped a lot, I was not representing B properly and i forgot I needed the current.