Magnetic Force

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.

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.

Okay, I understand that Fm=ILB or Fm=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.)

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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.