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A dielectric is placed in an electric field.

A dielectric is placed in an electric field. Correct Answer There is some charge induced on the surface of the dielectric

CONCEPT:

Conductors and dielectrics

  • A conductor has free electrons.
    • When a conductor is placed in an external electric field, these free electrons move and align themselves to create an induced charged density σ which produces an induced electric field such that the net field inside the conductor is zero. 
  • Dielectrics are non-conducting substances. They do not contain free electrons.
    • When a dielectric is placed in an external electric field, its molecules align themselves in such a way that charges are induced on the surfaces of the dielectric with having charge density σp, and thus an electric field is created inside the dielectric.
    • This induced electric field Ein has a value less than that of the external electric field.
  • Both these fields have opposite directions.
  • Therefore the magnitude of the net electric field inside a dielectric is less than that of the external electric field.
  • The direction of the net electric field inside the dielectric is the same as that of the external electric field.

EXPLANATION:

  •  Dielectrics are non-conducting substances. They do not contain free electrons. Therefore option 3 is wrong.
    • When a dielectric is placed in an external electric field, its molecules align themselves in such a way that charges are induced on the surfaces of the dielectric with having charge density σp, and thus an electric field is created inside the dielectric. Therefore option 1 is wrong and 2 is correct.
    • This induced electric field Ein has a value less than that of the external electric field. 
  • Both these fields have opposite directions.
  • Therefore the magnitude of the net electric field inside a dielectric is less than that of the external electric field.
  • The direction of the net electric field inside the dielectric is the same as that of the external electric field. Therefore option 2 is correct.

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