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Question
Explain briefly, using a proper diagram, the difference in the behavior of a conductor and a dielectric in the presence of an external electric field.
Solution
When a conductor is placed in an external electric field, the free charges present inside the conductor rearrange themselves in such a manner that the electric field due to induced charges opposes the external field within the conductor. After some time a static situation is achieved when the two fields cancel each other and the net electrostatic field in the conductor becomes zero.
Dielectrics are non-conducting in nature, i.e. they have no free charge carriers. Thus, in a dielectric, free movement of charges is not possible. In Dielectrics the external field induces dipole moment by stretching molecules of the dielectric. The collective effect of all the molecular dipole moments creates the net charge on the surface of the dielectric which produces a field that opposes the external field. However, the opposing field does not exactly cancel the external field but just reduces its value. So-net electrostatic field in a dielectric is non-zero.
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