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This is because the absolute permittivity of water is about 80 times greater than the absolute permittivity of air or free space.
Dielectric constant or relative permittivity
9192 .(1) %3D
When the same two charges are placed same distance apart in any medium other than vacuum, the force between them becomes
The quantity & is called absolute permittivity or just permittivity of the intervening medium. Dividing equation (1) by equation (2), we get,
The ratio () of the permittivity( )of the medium to the permittivity ( ) of free space is called relative permittivity ( ) or dielectric constant (k) of the given medium. Thus
So one can define dielectric constant in terms of forces between charges as follows :
The dielectric constant of a medium may be defined as the ratio of the force between two charges placed some distance apart in free space to the force between the same two charges when they are placed the same distance apart in the given medium.
Hence the Coulomb’s law for any material medium may be written as