Two charges each equal to $2\,\mu C$ are $0.5\,m$ apart. If both of them exist inside vacuum, then the force between them is.......$N$

According to Coulomb's Law, which is correct relation for the following diagram?

A particle of mass $1 \,{mg}$ and charge $q$ is lying at the mid-point of two stationary particles kept at a distance $'2 \,{m}^{\prime}$ when each is carrying same charge $'q'.$ If the free charged particle is displaced from its equilibrium position through distance $'x'$ $(x\,< \,1\, {m})$. The particle executes $SHM.$ Its angular frequency of oscillation will be $....\,\times 10^{8}\, {rad} / {s}$ if ${q}^{2}=10\, {C}^{2}$

Write general equation of Coulombian force on ${q_1}$ by system of charges ${q_1},{q_2},.......,{q_n}$.

An isolated solid metallic sphere is given $ + Q$ charge. The charge will be distributed on the sphere

Two small spheres each of mass $10 \,mg$ are suspended from a point by threads $0.5 \,m$ long. They are equally charged and repel each other to a distance of $0.20 \,m$. The charge on each of the sphere is $\frac{ a }{21} \times 10^{-8} \, C$. The value of $a$ will be ...... .

$\left[\right.$ Given $\left.g=10 \,ms ^{-2}\right]$