Explain dielectrics in detail and how an electric field is induced inside a dielectric .

Explanation

Induced Electric field inside the dielectric : When an external electric field is applied on a conductor the charges are aligned in such a way that an internal electric field is produced . The magnitude of the internal electric field is smaller than that of external electric field is small than that of external electric field . Therefore the net electric field inside the dielectric is not zero but is parallel to an external electric field with magnitude less than that of the external electric field . For example let us consider a rectangular dielectric slab placed between two oppositely charged plates ( capacitor ) as shown in the figure .

The uniform electric field between the plates acts as an external electric field `vecE_("ext") ` which polarizes the dielectric placed between plates . The positive charges are induced on one side surface and negative charges are induced on the other side fo surface . But inside the dielectric the net charge is zero even in a small volume . So the dielectric in the external field is equivalent to two oppositely charged sheets with the surface charge densities `+ sigma ` and `-sigma b`. These charges are called bound charges . They are not free to move like free electrons in conductors . This is shown in the figure .

For example the charged balloon after rubbing sticks onto a wall . The reason is that the negatively charged balloon is brought near the wall it polarizes opposite charges on the surface of the wall which attracts the balloon.