The presence of matter alters the net force acting between two charges. Explain.

Explanation

According to Coulomb's law, the effective force between two charges `q_(1)` and `q_(2)` placed in air or vacuum at a distance r from each other,
`F_(1)=(q_(1)q_(2))/(r^(2))`
Now, let the charges be placed in a medium of permittivity k. The effective force between the two charges now is,
`F_(2)=(q_(1)q_(2))/(kr^(2))`
Clearly, `F_(2)ltF_(1)`, since `kgt1`. So the effective force between two charges in presence of another matter is less. The charges induced in this medium is responsible for this decrease of force.