The Coulombian repulsive force between two alpha particles kept at a distance of $3 \ cm$ in air is . . . . . . .

Two identical charged spheres are suspended by strings of equal length. The strings make an angle of $30^{\circ}$ with each other. When they are immersed in a liquid of density $0.8 \, g \cdot cm^{-3}$,the angle remains the same. If the density of the material of the spheres is $1.6 \, g \cdot cm^{-3}$,find the dielectric constant of the liquid.

What is the net force on a $Cl^{-}$ ion placed at the centre of the $bcc$ structure of $CsCl$?

Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle $\theta$ with each other. When suspended in water,the angle remains the same. If the density of the material of the sphere is $1.5 \ g/cc$,the dielectric constant of water will be (Take density of water $= 1 \ g/cc$)

Two charges $q_1$ and $q_2$ are placed in vacuum at a distance $d$ and the force acting between them is $F$. If a medium of dielectric constant $4$ is introduced around them,the force now will be

Two point charges $+Q$ and $+q$ repel each other with a force of $100 \,N$. Keeping the distance between them unchanged, if $Q$ is increased by $10 \%$ and $q$ is decreased by $10 \%$, the force of repulsion between them will: