Balancing Magnetic & Gravitational Forces: A Current-Balance Investigation

[Kylah]

1. The following information describes a current-balance investigation. The current in the solenoid that generates the magnetic field was held constant and the length of wire in the end of the loop in the field was 0.050 m long.
i168.photobucket.com/albums/u173/pleasetheworld/p3.jpg

a) Calculate the magnetic force on the end of the loop to balance the gravitational force on the string. Record the values in the data chart.
i168.photobucket.com/albums/u173/pleasetheworld/p4.jpg

Okay, I understand that F_m=ILB or F_m=qvB, but I'm not sure how to find the magnetic force if I don't know the current or magnitude of the magnetic field. I'm assuming I have to find the force of gravity, but I'm not sure where to go from there. I'm sure I can figure out the rest of the question (finding the magnetic field, graphing, etc.) if I can get past part a. If somebody could help me out with the first part I would really appreciate it. I just need an idea as to what formula to use (or how to adapt it to fit the question.)

 

[Nick89]

Haven't looked at the pictures but it seems to me that there is some loop / wire with some current that is being held up by a magnetic field?
Seems to me all you have to do is balance the magnetic force (which you have wrote down) with the gravitational force (I assume you know the mass of the loop/wire being help up?).
From that, you can find B.

 

[Texag]

This is my first post, so I am sorry that I cannot provied fancy symbols and formulas I have seen others use.(Help would be appreciated on this)

The magnetic field inside the solenoid is B = (mu0)(Number of loops per unit length)(Current) which is found using amperes circuital law.

 

[Nick89]

I think the topic starter realizes that, but he says he does not know the current that runs through the solenoid, so you cannot find B from that...

Also, the fancy symbols and formulas are made using \LaTeX. Look it up on this forum, there is a help thread for it. Also, you can click on any formula and it will show you how you can make it.