Magnetic fields are sometimes measured by balancing magnetic forces against known mechanical forces. Your task is to measure the strength of a horizontal magnetic field using a 12-cm-long rigid metal rod that hangs from two nonmagnetic springs, one at each end, with spring constants 1.3 N/m. You first position the rod to be level and perpendicular to the field, whose direction you determined with a compass. You then connect the ends of the rod to wires that run parallel to the field and thus experience no forces. Finally, you measure the downward deflection of the rod, stretching the springs, as you pass current through it.
Your data are as follows:

Current, I (A) Deflection, delta y (mm)
1.0 4
2.0 9
3.0 12
4.0 15
5.0 21

You want to determine the magnetic field strength by graphing the data. Select the appropriate variables to graph on each axis that will produce a straight-line graph with either a slope or intercept that will allow you to determine the field strength.