Electric displacement is given as: D=εoE+P where: E: External electric field P: Polarisation εo: Permittivity of free space
It is related to the free charge density by, D.n^=σ
Note: 1. Electric Displacement is directly related to the free surface charge density in a medium instead of the electric field. 2. On change of medium of an electric field, electric field changes but electric displacement remains the same.
Relationship between Electric Displacement and Electric field
Electric displacement is given by: D=εoKE where εoK: Permittivity of the medium