A conductor of electricity is a material or substance which allows to flow of electric current
when subjected to a potential difference. This electric current is continue to flow till the potential deference
exists. For a given potential difference, the density of electric current in conductor represents how efficient a conductor is. Based on the resistivity
can be classified into two categories i.e. low resistivity/high conductivity material
and high resistivity/low conductivity materials.
This general properties of a conductor are listed below –
In equilibrium condition the conductor exhibits the following properties –
- The electric filed inside the conductor is zero
- The charge density inside the conductor is zero
- Free charge exists only on the surface of the conductor
- At the conductor surface, the electric field is normal to the surface.
Resistance of Electric Conductor
Conductors of electricity generally possessed very low resistance for flow of electricity. Ideally the resistance
of a perfect conductor is zero. However, practically the resistivity of conductors varies from low to high. The conductor having low resistivity/high conductivity are used as conductor for winding of electrical machines, for transmission lines
, for electrical contact, earth wire etc. The conducting materials having high resistivity/low conductivity are used for making filaments incandescent lamp
and heating elements for electric heaters, Ovens, furnaces.
Inductance of Electric Conductor
When a conductor is used on AC supply a magnetic flux
is produced. Which is consists of two parts. Internal flux and external flux. The value of internal flux is very low as compare to external flux. Due to this flux linkage to conductor itself an inductance is come into picture. This inductance
results in extra voltage drop
in conductor. Moreover, this inductance is also effect the current distribution over the cross-section area of conductor. Due to which, current prefers to flow through outer part of cross-sectional area. This effect is called Skin effect. This current distribution over cross-sectional area is also effected by the flux linkage to conductor due to current following through nearby conductor
. This is called Proximity effect of these both effects skin effect and Proximity effect exist only for AC supply. These effects do not exist for DC supply, as the flux
produced by DC supply remains constant over the time.
Electric Field Inside the Conductor is Zero
The electrical field inside a perfect conductor is zero. If the electric field
exists inside the conductor, it will extract a force on electron and accelerate them. But in equilibrium condition the net force on electron is zero. Hence, electric filed does not exists inside the conductor. Means the electric field must be external to the conductor. This property of conductor make it suitable to be used for electrostatic shielding for electrical equipment.
Charge Density Inside the Conductor is Zero
This electric charge does not exists inside the conductor. The mutual electrostatic repulsion force, between like charges i.e. electrons, demands that the electrons must be as far as possible. This electrostatic repulsion force pushes the electrons to the surface on conductor. Due to which there is no electric charge exists inside the conductor results in zero charge density inside the conductor.
Free Charge Exists Only on the Surface of the Conductor
As discussed above, the charge particle does not exist inside the conductor. Due to electrostatic repulsion force, the electrons move to outer surface of the conductor. Due to which there is no electric charge exists inside the conductor. Hence, free electric charge exits only on the surface of the conductor.
Conductor Surface, The Electric Field is Normal to the Surface
If we go through the boundary condition of dielectric to conductor, the electric field is normal to the surface of conductor and tangent part of electric field
to surface is zero. Means, the electric field intensity is normal to the surface of conductor
and the tangential part of electric field intensity is zero.