1. The problem statement, all variables and given/known data Lightning strikes a lightning rod that is a thin, hollow cylinder with a radius of 1.0 cm with a peak current of 250 kA. What is the magnetic force on an infinitesimal segment (vertical line) of current of width dx and length L?  2. Relevant equations F = I[integral](dl)xB 3. The attempt at a solution I calculated the magnetic field strength of B = 5.01 T I'm not really sure how to start this? How do I incorporate the width dx?