Conductors Electric Currents
We know that atoms and molecules are made of negatively charged electrons and positively charged nuclei, which are bound to each other and are thus not free to move. A material (bulk matter) is composed of many atoms/molecules. In a material the molecules are so closely packed that some of the electrons in it are no longer attached to individual nuclei, but free to move inside the matter like molecules in a gas. Such electrons are called free electrons. These free electrons move under the effect of electric field, in a definite direction resulting in a current in the material those materials which have large number fo free electrons and develop strong electric currents in them when an electric field is applied are generally called conductors.
There are some other materials in which the electrons will be bound and they will not be accelerated even if the electric field is applied no current on applying electric field such materials are called insulators. For example wood plastic rubber etc,
Atoms are tightly bound to each other. There are large numbers of free electrons in them which will be responsible for the strong current in them when electric field is applied on them.
In case of a liquid conductor like electrolytic solution there are positive and negative charged ions which can move on applying electric field causing the electric current.
Here, we will discuss only about solid conductors in which the positive ions are at fixed positions and the current is carried by the negatively charged electrons.
When no electric field is applied on a solid conductor, the free electrons move lie molecules in a gas due to their thermal velocities. There is no preferential direction of the velocities of the electrons. Therefore, at a cross-sect in of the conductor, the number of free electrons travelling in one direction will be equal to the number of free electrons travelling in ht opposite direction. Due to sit there is no net flow of electric charge in a direction inside the conductor and hence no current in it.
When an electric field is applied on a solid conductor in the shape of cylinder of circular cross-section by attaching positively and negatively charged circular discs of a dielectric of the same radius as that of the solid conductor at the two ends as shown in an electric field is setup in the conduct5or from positive charged disc towards negative charged disc. Due to this electric field the free electrons in the conductor will be accelerated towards the positive disc side, in order to neutralize the charges of discs. The motion of the electrons will be there till the electric field inside the conductor exists. In this situation, there will be a current for a very short time called transient current in the conductor.
If we apply a steady eclectic field in the body of conductor by connecting a cell or battery across the two ends of a conductor them there will be a steady cure dent in conductor rather than a transient current.
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