Magnetic force in a solenoid. I would like to know how to calculate the magnetic force in a solenoid, by the equation of B=LNI; I have only reached the magnetic field. However, if I have a bar that moves inside the solenoid, the equations that I know bothF=qvB and F=ILB, are equations that do not describe the movement that I appreciate mechanically. There is another way to express the magnetic force in SOLENOIDS.