Magnetic Field

The ultimate individual unit of magnetism in any magnet is:

The strength of a bar magnet is maximum at its center. (T/F)

Read the following paragraph and answer the questions given below.
Ferromagnetic substances are those which get strongly magnetized when placed in an external magnetic field. They have strong tendency to move from a region of weak magnetic field to strong magnetic field, that is, they get strongly attracted to a magnet. The individual atoms (or ions or molecules) in a ferromagnetic material possess a dipole moment as in a paramagnetic material. However, they interact with one another in such a way that these spontaneously align themselves in a common direction over a macroscopic volume called domain. Each domain has a net magnetization. Typical domain size is 1 mm and the domain contains about atoms. In the first instant the magnetization varies randomly from domain to domain and there is no bulk magnetization. When we apply an external magnetic field the domains orient themselves in the direction of and simultaneously that domain oriented in the direction of grows in size. We may wonder as to what happens when the external field is removed, in some ferromagnetic materials the magnetization persists. Such materials are called hard magnetic materials of hard magnets. Alnico, an alloy of iron, aluminium, nickel, cobalt and copper is one such material. There is a class of magnetic materials in which the magnetization disappears on removal of the external field. Soft iron is one such material. Such materials are called soft ferromagnetic materials. There are number of elements which are ferromagnetic. Iron, cobalt, Nickel, gadolinium etc. The ferromagnetic property depends on temperature. At high enough temperature a ferromagnet becomes a paramagnet. That domain structure disintegrates with temperature. This disappearance of magnetization with the temperature is gradual.

Explain Biot-Savart's law for a small current-carrying conductor.

A proton enters into a magnetic field of intensity Tesla with velocity at an angle of 30° with the field. Calculate the magnitude of force acting on the proton due to this field.

Define the coefficient of self-induction and find an expression for it for a solenoid.

Derive an expression for magnetic force. How is the direction of magnetic force determined?

What is displacement current?