Ahall-effect probe to measure magnetic field strengths needs to be calibrated in a known magnetic field. although it is not easy to do, magnetic fields can be precisely measured by measuring the cyclotron frequency of protons. a testing laboratory adjusts a magnetic field until the proton's cyclotron frequency is 9.60 mhz . at this field strength, the hall voltage on the probe is 0.540 mv when the current through the probe is 0.143 ma . later, when an unknown magnetic field is measured, the hall voltage at the same current is 1.736 mv .a) what is the strength of this magnetic field?