Читать книгу The ESD Control Program Handbook - Jeremy M. Smallwood - Страница 25

Coulomb's law shows that the field due to a point charge is proportional to the charge and inversely proportional to the distance from it squared (Cross 1987).

Permittivity (dielectric constant), ɛ, was defined to give a convenient constant of proportionality in this relation.

For air, the permittivity is very close to the permittivity of free space ɛ₀ (vacuum) ɛ = ɛ₀ = 8.8 × 10⁻¹² Cm⁻¹. Other materials have different permittivity and affect field strengths correspondingly. In general, a dielectric material has a permittivity greater than air. This is conveniently expressed as a relative permittivity ɛ_r, and the permittivity is given by

Polymers often have relative permittivity in the range 2–3 and many other materials in the range 2–10. Materials such as ceramics can have far higher permittivity.