If two charges of $1$ coulomb each are placed $1 \,km$ apart, then the force between them will be ........... $N$

Two small metal balls of different masses $m_1$ and $m_2$ are connected by strings of equal length to a fixed point. When the balls are given equal charges, the angles that the two strings make with the vertical are $30^{\circ}$ and $60^{\circ}$, respectively. The ratio $m_1 / m_2$ is close to

Similar charges are placed at corners of a square and a charge $q_0$ is placed at it's centre find net force on it

A total charge $Q$ is broken in two parts ${Q_1}$ and ${Q_2}$ and they are placed at a distance $R$ from each other. The maximum force of repulsion between them will occur, when

A point charge $q_1=4 q_0$ is placed at origin. Another point charge $q_2=-q_0$ is placed at $x =12\,cm$. Charge of proton is $q_0$. The proton is placed on $x$-axis so that the electrostatic force on the proton in zero. In this situation, the position of the proton from the origin is $..........cm$.

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