The correct answer is:
<span>Point charges must be in a vacuum.
In fact, the usual form for of the Coulomb's law is:
</span>
<span>where
</span>
is the permittivity of free space
<span>q1 and q2 are the two charges
q is the separation between the two charges
However, this formula is valid only if the charges are in vacuum. If they are in a material medium, the law is modified as follows:
</span>
where
is the relative permittivity, which takes into account the dielectric effects of the material.
<span>Point charges must be in a vacuum.
In fact, the usual form for of the Coulomb's law is:
</span>
<span>where
</span>
<span>q1 and q2 are the two charges
q is the separation between the two charges
However, this formula is valid only if the charges are in vacuum. If they are in a material medium, the law is modified as follows:
</span>
where