### 1.torque on a magnetic dipole in a magnetic field 2.hysteresis 3.does a magnetic monopole exist? justify and how magnetic field produced? 4. eddy current

1.The usual model of a magnetic dipole is a small current loop.  If the loop has area A and the current in the loop is I, then the magnitude of the dipole is IA, and its vector is perpendicular to the loop.IA=m, where m is the magnetic dipole moment and is a vector.The torque is parallel to the magnetic field, but perpendicular to the dipole moment.
the torque, N = m x B where B is the field strength.

2.When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. It must be driven back to zero by a field in the opposite direction. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again.

3.We know that when a magnet is divided into two parts,both of them will have a north pole and a south pole, instead of forming monopole. In more technical terms,a magnetic monopole would have a net magnetic charge. But such particles have never been observed and recent searches have still not found any. But the grand unified theory and super string theory predicts their existence.

4.Eddy currents are electric currents induced within conductors by a changing magnetic field in the conductor. These fields can cause repulsive, attractive, heating effects etc. The stronger the applied magnetic field, or the greater the electrical conductivity of the conductor, or the faster the field changes, then the greater the currents that are developed and the greater the fields associated with them.