Relative Permittivity Calculator

At a glance:Relative permittivity (εr, also dielectric constant): an index of a substance's ability to polarise under an applied electric field, defined as εr=ε/ε0=C/C₀, where ε is the absolute permittivity (F/m), ε0=8.854187817×10⁻¹² F/m is the vacuum permittivity, C is the capacitance of a parallel-plate capacitor filled with the dielectric, and C₀=ε0·A/d is the same-size vacuum capacitance. Back-calculated from capacitance: εr=C·d/(ε0·A). Mechanism: the applied field displaces bound charges in the medium (electronic, ionic, orientational polarisation), producing a reverse polarisation field that weakens the total field and raises the charge-storage ability. Classification: (1) vacuum and gases — air εr≈1.0006, H₂ 1.00026, CO₂ 1.00098; (2) non-polar liquids — benzene 2.28, CCl₄ 2.24, transformer oil 2.2; (3) polar liquids — water 80.1 (25°C), methanol 33, ethanol 24, glycerol 42; (4) solid insulators — polyethylene 2.25, polypropylene 2.2, mica 5.4, glass 5–10, ceramic 6–8, silica 3.9; (5) ferroelectrics — BaTiO₃ 1000–10000, SrTiO₃ 2000, PZT 300–3000. Temperature and frequency dependence: polar media lose εr at high frequency (water drops to 30 at 25 GHz). Classic example: 1 cm² plate, 1 mm gap, vacuum C₀=ε0·A/d=8.854e-12×0.01/0.001=8.854e-11 F; water-filled C=εr·C₀=80×8.854e-11=7.08e-9 F. History: Faraday studied permittivity in 1837; Coulomb had already observed that charge force weakens in a medium. Applications: (1) capacitors — ceramic capacitors use BaTiO₃ for high density; (2) microwave heating — water molecules absorb at 2.45 GHz by polarisation; (3) dielectric sensing — soil-moisture measurement; (4) optics — refractive index n=√εr; (5) insulation — high εr raises capacitance and withstand voltage.