radius of the coil, I is the current through the coil and x is the distance from the center this equation length of the coil wire must be short enough to be negligible. B = 2 x2 + R2 2 This second equation is used to calculate the magnetic field of a long solenoid. of free space, n is the number of turns per unit length, and I is the current through direction of the field is straight down the axis of the solenoid so the use this equation coil must be substantially longer than the diameter of the coil. The accuracy of these equations was determined by calculating the magnetic field usi and then comparing these values to the measured values obtained in the experiment