chap7-mag三fie(zq).ppt

Discussion Although the torque expression was derived for a rectangular loop, the result is valid for a loop of any shape. The equilibrium position of the coil . the steady equilibrium position. the unsteady equilibrium position. Under the action of the torque, the magnetic moment 磁矩 always tries to turn to the direction of external magnetic field. Example Z o X Y I A coil of half circle is set in the uniform magnetic field parallel to the coil plane in the beginning instant, the radius of coil R=0.5m, I=10A, B=0.5T. Find (1) the torque of magnetic force on the coil in the beginning instant. (2) The work done by the torque of magnetic force when the coil rotated by angle π/2 from the initial position. Example: Show that the magnetic dipole moment p of an electron orbiting a hydrogen atom is related to the orbital momentum L of the electron by p =eL/(2m). Solution: Another way to measure magnetic field: The one of magnetic dipole moment when a coil is in stable-equilibrium. Direction of : Magnitude of : [M]= T·A·m2 =N·m SI unit of the torque: 1. Classification of magnetic materials When the interior of a solenoid is filled with some material of relative permeability ?r (相对磁导率), Ferromagnetism (铁磁质) Paramagnetism (顺磁质) Diamagnetism (抗磁质) 7-9 The Magnetic Media in a Magnetic Field 2. Magnetization(磁化)of magnetic materials Cross area of solenoid When the interior of a solenoid is fully filled with some isotropic material ?r , it will be magnetized (长直螺线管内部充满均匀的各向同性介质，将被均匀磁化). Taking the paramagnetic material as an example, each molecular in it is equivalent to a loop current: To express the extent to which a given medium is magnetized, a vector quantity, magnetization 磁化强度, is introduced: The unit of is A/m. It can be proved, The net bound current enclosed in a closed loop L equals to the circulation环流 of magnetization along the closed loop. and Take notes! 3. Circulation theorem with magnetic materials Let, t