Search coil by computer to determine displacement in multiple dimensions. Additionally, a second search coil can be added to measure torsional rotation. A more crude search coil also called exploring coil is also used in laboratory experiments in schools to measure the magnetic field in a certain region of space. In this case the search coil consists of a simple wire coil or solenoid connected to a sensitive ammeter or galvanometer. The coil is placed in the magnetic field to be measured and quickly withdrawn to a region of space with a negligible magnetic field. As the search coil moves the magnetic
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: