Coulomb's Law states that the force between two bodies varies inversely with the square of the distance r between them, and is proportion to the product of the charges. In the equation below the charges have sign, positive or negative,
Ifandhave the same sign thenis positive. This means that the charges repel each other and the distance between them tends to increase sois positive.
Ifand have opposite signs thenis negative. This means that the charges attract each other and the distance between them tends to decrease so is negative.
These two statements can be summarised as, 'like charges repel, unlike charges attract'.
The constant of proportionality k is equal to