If a matter is present between the two charges then it net force between th two charges. This is because of some permittivity of the meduim or matter.

 

Say its relative permittivity is , then force betwen the two charges is altered as

 

F' = F/ 

 

Where F =  q₁q₂/4₀ = force between the the charges in the absence of matter

 

And F' = force between the charges in the prescence of matter.

 

The physical explantion of this phenomenon is easy.

As when the matter say dielectric is introduced between teh point charges then depending on the condition whether the dielectric material is

a) Polar material or

 

b) Non-polar material.

 

The rescence of elctric field between the two charges tends to polarise the dielectric or it aligns the microscopic dipole moments in the direction of external electric field. Thus generating internal electric field resulting into the altering of force between the point charges.