Magnetism and Matter Test -3

A permanent magnet is a ferromagnetic substance that does not lose their ferromagnetic properties for a long period of time at room temperature. Since they retain their magnetic properties for quite a long time they are called permanent magnets.

The individual atoms in a ferromagnetic material possess a dipole moment as in a paramagnetic material. However, they interact with one another in such a way that they spontaneously align themselves in a common direction over a macroscopic volume called domain.

Thus we can say that in a permanent magnet at room temperature the dipoles are perfectly aligned.

As μ_r, < 1 for a substance X, it must be diamagnetic

And μ_r, > 1 for Y, then it must be paramagnetic

The hysteresis curve represents the relation between the magnetic induction B or intensity of magnetization I of a ferromagnetic material with magnetic intensity H.

An electromagnet is necessary for the material that even if the current is turned off, the material losses its magnetic field. So, it should be made from such a material that its retentivity is very high. And there must be enough coercion force for the material which can restore its pre-magnetization state. For that its coercivity should be as minimum as possible.

$$Answer:$$

Hence, option B is the correct answer. 

A magnet placed in a magnetic field will feel a torque that will try to align the magnet with the magnetic field.This magnetic torque is the basis for how compasses work.

Answer is D.

The magnetic field at any point in space is a vector quantity. This means there is a direction associated with the field as well as a field strength. Consider the arrow below:
The direction of the magnetic lines of force can be thought of as the direction of the magnetic field. The length of the  magnetic lines of force can be thought of as the strength of the field, i.e. the longer the lines, the stronger the field. 

Diamagnetic substances are those which are freebly repelled by the magnetic field.
$$\therefore$$ Copper, Hydrogen, Silver are diamagnetic as their atoms have net magnetic dipole moment zero.

Ferromagnetic materials exhibit a long-range ordering phenomenon at the atomic level which causes the unpaired electron spins to line up parallel with each other in a region called a domain. Within the domain, the magnetic field is intense, but in a bulk sample the material will usually be unmagnetized because the many domains will themselves be randomly oriented with respect to one another. Ferromagnets will tend to stay magnetized to some extent after being subjected to an external magnetic field. This tendency to "remember their magnetic history" is called hysteresis.  Nickel, iron and cobalt are such materials. Ferromagnetic materials exhibit a long-range ordering phenomenon at the atomic level which causes the unpaired electron spins to line up parallel with each other in a region called a domain. Within the domain, the magnetic field is intense, but in a bulk sample the material will usually be unmagnetized because the many domains will themselves be randomly oriented with respect to one another.Ferromagnets will tend to stay magnetized to some extent after being subjected to an external magnetic field. This tendency to "remember their magnetic history" is called hysteresis.  Nickel, iron and cobalt are such materials.

The Curie temperature($$T_C$$) is the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism, that is, they go from becoming ferromagnetic to paramagnetic.

The following are properties of magnetic lines of force:

A magnetic field is a vector field that describes the magnetic influence of electrical currents and magnetic materials. In everyday life, the effects of magnetic fields are most readily encountered with nearby permanent magnets, which pull on magnetic materials (such as iron) and attract or repel other magnets.

When current is passed through a current carrying inductor, energy is stored in it in form of magnetic field.