Electric susceptibility is a measure of how easily a material can be polarized by an external electric field, while relative permittivity is a measure of how much an electric field is weakened when passing through a material. In other words, electric susceptibility is a property of the material itself, while relative permittivity is a property of the material's interaction with an electric field.
Electric susceptibility and relative permittivity are related by the equation X = ε - 1, where X is the electric susceptibility and ε is the relative permittivity. This shows that electric susceptibility is directly proportional to relative permittivity.
The unit of measurement for electric susceptibility is typically expressed in units of volume, such as m^3/V, while relative permittivity is a dimensionless quantity.
Electric susceptibility and relative permittivity both play a role in determining the strength and direction of electric fields within a material. Materials with a higher electric susceptibility will be more easily polarized by an electric field, while materials with a higher relative permittivity will weaken the electric field passing through them.
Electric susceptibility and relative permittivity are important properties in understanding and predicting the behavior of materials in the presence of electric fields. They are used in a variety of practical applications, such as in the design of capacitors, insulators, and other electronic devices.