How Should I Prepare for Moving Charge and Magnetic Classes?

What is Magnetism:

This is a physical property which is encouraged by some magnetic fields. The current which are electric and the magnetic property of the particles will give some magnetic fields. These fields will act on other current and magnetic moments. This is the other important aspect other than electromagnetism. We can take the example of ferromagnetic materials and these are very strongly attracted by some magnetic field and thus they can be said to be able to magnetised. These thus can become magnetic things. They become permanent magnets and they in turn will produce their own magnetic fields. It is also possible to demagnetise another magnet. We can cite some example of some ferromagnets which are iron, cobalt and nickel for example. These also have alloys which are ferromagnetic as well. Some of the rare metals like samarium are examples but they do not show much attribute to the ferromagnetic properties. When we say ferro it refers to iron and here permanent magnetism is first observed in magnetite which is a natural iron ore.

When we say magnetism we can say all substances will show magnetism. The ferromagnets will be classified as to how susceptible they are. The term ferromagnetism is responsible for the magnetic properties most of the time and in reality they are several types of magnetism.

Some of the basic para magnetic substances like aluminium and oxygen are very weakly attracted to the moving charge and magnetic field. The diamagnetic field such as carbon and copper are repelled also in such a case in a weak way, while the anti ferromagnetic materials such as chromium are more entwined and complex relating to the magnetic field.

Whatever be the force on the magnet be it ferromagnetic or anti ferromagnetic the materials will will be too weak to be detected and thus this requires more sophisticated instruments and so in the laymen term we call these non magnetic substances or materials. Hence when we say magnetic state the material it will depend on material or temperature or pressure and some magnetic field.

How does Magnetism occur and this happens by two ways:

  1. Electric Current
  2. Magnetic moments for particles

When the material is taken there are many electrons on it and thus they are arranged in such a way that their magnetic moments will cancel each other.

This happens because the electrons will combine with each other and into pairs and they have opposite magnetic moments. Here the electrons will arrange themselves in a way that the magnetic moment for them is cancelled by the opposite electron moment. Thus when we see the configuration of the electron there are also unpaired electrons and sub-shells which are not filled.

The magnetic properties of the materials do come from the magnetism of the atoms and their electrons which are in orbit. The magnetic moments of the nuclei from the atoms are much smaller than the magnetic moments of the electrons. This is therefore negligible.

What Are Moving Charges and how it is related to Magnetism?

This is a physical property for matter that experiences a force when it is placed in an electromagnetic field. The charges can thus be negative or positive. They are either carried by electrons or protons. The like charges will repel and unlike charges will attract each other. Where there is no net charge it is called neutral. This is electrodynamics.

This is a conservable property and thus if we subtract the negative charge from the positive charge then it is known to not have a change. It is carried by particles and negative charge is carried by electrons and positive charge is carried by protons and this happens in the nuclei of the atoms.

If we have more electrons than protons then it will be negative charge and visa versa. If the number is equal then it will have neutral charge. The SI unit is Coulomb and it is named after Charles August in De Coulomb.  These charges will produce electric fields and a moving charge will also produce a magnetic field. If there is interaction then there is possibility of getting an electromagnetic field. This is the source of all the electromagnetic forces or Lorentz forces and this is one of the four fundamental forces in the field of Physics. If we talk of Photon mediated or induced interactions then this happens among the charged particles and this is therefore called Quantum Electrodynamics.

Can you solve the question: A long cylindrical conductor of radius R carries a current i as shown in the figure. The current density J varies across the cross-section as J = kr^ (2), where, k is a constant. Find an expression for the magnetic field B at a distance r (lt R) from the axis?