Question

Question 1. Explain, on the atomic level, the physical mechanism underlying two of the three forms of magnetic materials described in the text, paramagnetic, diamagnetic, and Ferromagnetic. 2. Aluminum is paramagnetic. Why won't a typical refrigerator magnet stick to an aluminum can? 3. Describe how bar magnets produce a force on each other

Answer 1

1 )

Classification Of Magnetic Materials :

All matter respond in one way or the other when subjected to the influence of a magnetic field. The response could be strong or weak, but there is none with zero response ie, there is no matter which is non magnetic in the absolute sense. Depending upon the magnitude and sign of response to the applied field , and also on the basis of effect of temperature on the magnetic properties, all materials are classified broadly under 3 categories.

1. Diamagnetic materials   2. Paramagnetic materials, 3. Ferromagnetic materials

                         Two more classes of materials have structure very close to ferromagnetic materials but possess quite different magnetic effects. They are     i. Anti ferromagnetic materials    and ii . Ferri magnetic materials

         

1.Diamagnetic materials:

Diamagnetic materials are those which experience a repelling force when brought near the pole of a strong magnet. In a non uniform magnetic field they are repelled away from stronger parts of the field.

   In the absence of an external magnetic field , the net magnetic dipole moment over each atom or molecule of a diamagnetic material is zero.

Ex: Cu, Ag, Au, Bi, Sb, Pb, NaCl, H₂O, Zn and rare gases.

2.Paramagnetic materials:

Paramagnetic materials are those which experience a feeble attractive force when brought near the pole of a magnet. They are attracted towards the stronger parts of magnetic field. Due to the spin and orbital motion of the electrons, the atoms of paramagnetic material posses a net intrinsic permanent moment.

Susceptibility χ is positive and small for these materials. The susceptibility is inversely proportional to the temperature T.

                    χ α 1/T

                   χ = C/T            where C is Curie’s temperature.

Below superconducting transition temperatures, these materials exhibit the Para magnetism.

Examples: Al, Mn, Pt, Na, CuCl₂, O₂, crown glass etc.

3.Ferromagnetic Materials:

Ferromagnetic materials are those which experience a very strong attractive force when brought near the pole of a magnet. These materials, apart from getting magnetized parallel to the direction of the applied field, will continue to retain the magnetic property even after the magnetizing field removed. The atoms of ferromagnetic materials also have a net intrinsic magnetic dipole moment which is due to the spin of the electrons.

Susceptibility is always positive and large and it depends upon temperature.

                    χ = C / (T- θ) ( only in paramagnetic region i.e., T > θ)

                                                θ is Curie’s temperature.

When the temperature of the material is greater than its Curie temperature then it converts into paramagnetic material.

Examples: Fe, Ni, Co, MnO.

2 )

the big magnets can be made by tiny magnets,

so when comes to tiny magnets and these kept in strong magnetic field it will come together

and stick to magnet. aluminum did not have such tiny magnets.

so typical refrigerator magnet stick to an aluminum it will not happen.