Magnetic field by that loop. Ampère's law is always valid for steady currents and can be used to calculate the -field for certain highly symmetric situations such as an infinite wire or an infinite solenoid. In a modified form that accounts for time varying electric fields, Ampère's law is one of four Maxwell's equations that describe electricity and magnetism. A charged particle moving in a -field experiences a "sideways" force that is proportional to the strength of the magnetic field, the component of the velocity that is perpendicular to the magnetic field and the charge of the particle. This force is known
Helmholtz coil coil is "n" and the current through the coils is "I", then the magnetic field B at the midpoint between the coils will be given by where formula_15 is the permeability of free space . Start with the formula for the on-axis field due to a single wire loop which is itself derived from the Biot–Savart law: Here The Helmholtz coils consists of "n" turns of wire, so the equivalent current in a one-turn coil is "n" times the current "I" in the "n"-turn coil. Substituting "nI" for "I" in the above formula gives the field for an "n"-turn coil: