CBSE Class 12-science Answered
Flow of electric charges of a metallic conductor plzz explain me
Asked by biruapreety734 | 29 Nov, 2020, 07:42: PM
Expert Answer
An electric charge will experience a force if an electric field is applied. If it is free to move, it will thus move contributing to a current.
Bulk matter is made up of many molecules. These molecules are so closely packed that the electrons are no longer attached
to individual nuclei. In some materials known as insulators ( example :- plastic , wood etc) , the electrons will still be bound,i.e.,
they will not accelerate even if an electric field is applied. In other materials, notably metals that are called as conductors,
some of the electrons are practically free to move with in the conductor. Hence conducting materials develop electric currents
in them when an electric field is applied.
If we consider solid conductors, atoms are tightly bound to each other so that the current is carried by the negatively charged electrons.
Let us consider first the case when no electric field is present. The electrons will be moving due to thermal motion
during which they collide with the fixed ions. An electron colliding with an ion emerges with the same speed as before the collision.
However, the direction of its velocity after the collision is completely random. At a given time, there is no preferential direction
for the velocities of the electrons. Thus on the average, the number of electrons travelling in any direction will be equal to the
numberof electrons travelling in the opposite direction. So, net electric current will be zero in conductor in absence of electric field.
Let us now see what happens to a conductor if an electric field is applied. Let us imagine the conductor in the shape of a cylinder
of radius R as shown in above figure. Suppose we now take two thin circular discs of a dielectric of the same radius and
put positive charge +Q distributed over one discand similarly –Q at the other disc. We attach the two discs on the two flat surfaces
of the cylinder. An electric field will be created and is directed from the positive towards the negative charge.
The electrons will be accelerated due to this field towards+Q. They will thus move to neutralise the charges.
The electrons, as long as they are moving, will constitute an electric current. Hence in this situation , there will be a current
for a very short while and no current there after.
We can also imagine a mechanism where the ends of the cylinder are supplied with fresh charges to make up for
any charges neutralised by electrons moving inside the conductor. In that case, there will be a steady electric field in the body
of the conductor. This will result in a continuous current rather than a current for a short period of time. Mechanisms,which maintain
a steady electric field are cells or batteries .
Hence if electric field is maintained in a conductor using EMF of cells or battery ,
then electric current is continuously established in conductor .
Answered by Thiyagarajan K | 30 Nov, 2020, 10:10: AM
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