Two particles of equal mass $m$ and charge $q$ are placed at a distance of $16 \, cm$. They do not experience any net force. The value of $\frac{q}{m}$ is

Three charges are placed as shown in the figure. The magnitude of $q_1$ is $2.00\, \mu C$,but its sign and the value of the charge $q_2$ are not known. Charge $q_3$ is $+4.00\, \mu C$,and the net force on $q_3$ is entirely in the negative $x-$ direction. The magnitude of $q_2$ is

For any fixed distance,the electromagnetic force between two protons is $10^n$ times the gravitational force between them. Then $n=$

$A$ charge $q_1$ exerts some force on a second charge $q_2$. If a third charge $q_3$ is brought near,the force of $q_1$ exerted on $q_2$:

Two identical conducting spheres with negligible volume have $2.1 \, nC$ and $-0.1 \, nC$ charges,respectively. They are brought into contact and then separated by a distance of $0.5 \, m$. The electrostatic force acting between the spheres is $.......... \times 10^{-9} \, N$. [Given: $\frac{1}{4 \pi \varepsilon_{0}} = 9 \times 10^{9} \, N \cdot m^{2}/C^{2}$]

Write some important points for the vector form of Coulomb's law.