relative permittivity, \(\varepsilon_{\text{r}}\)
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https://doi.org/10.1351/goldbook.R05273
Ratio of the electric field strength in vacuum to that in a given medium. It was formerly called the dielectric constant.
Source:
Green Book, 2
nd
ed., p. 14 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)