Magnetic field lines form in concentric circles around a cylindrical current-carrying conductor, such as a length of wire. The direction of such a magnetic field can be determined by using the "right hand grip rule" (see figure at right). The strength of the magnetic field decreases with distance from the wire. (For an infinite length wire the strength is inversely proportional to the distance.) Bending a current-carrying wire into a loop concentrates the magnetic field inside the loop while weakening it outside. Bending a wire into multiple closely spaced loops to form a coil or "solenoid" enhances this effect. A device so
Magnetic field and in oersteds (Oe) in cgs units. The precision attained for a magnetic field measurement for Gravity Probe B experiment is 5 attoteslas (); the largest magnetic field produced in a laboratory is 2.8 kT (VNIIEF in Sarov, Russia, 1998). The magnetic field of some astronomical objects such as magnetars are much higher; magnetars range from 0.1 to 100 GT (10 to 10 T). See orders of magnitude (magnetic field). Devices used to measure the local magnetic field are called magnetometers. Important classes of magnetometers include using induction magnetometer (or search-coil magnetometer) which measure only varying magnetic field, rotating coil