What is `local field’ in a dielectric?

The term 'local field' in a dielectric refers to the electric field experienced by an atom within the dielectric material. This field is a combination of the applied external field and the fields produced by the polarization of neighboring atoms.

Here are the steps to understand it:

1. When an external electric field is applied to a dielectric material, it polarizes the atoms or molecules of the material. This means that it causes a displacement of the positive and negative charges within the atoms or molecules, creating a dipole moment.

2. This polarization of the atoms or molecules creates its own electric field, which adds to the external field.

3. The total electric field experienced by an atom within the material is therefore the sum of the external field and the fields due to the polarization of all the other atoms. This is known as the 'local field'.

4. The local field is therefore generally stronger than the external field, because it includes the contributions from the polarized atoms or molecules. This enhancement of the electric field within the dielectric is a key factor in its ability to store energy when placed in an electric field.