Three charges $-q, Q$ and $-q$ are placed respectively at equal distances on a straight line. If the potential energy of the system of three charges is zero,then what is the ratio of $Q: q$ ?

$A$ short electric dipole has a dipole moment of $16 \times 10^{-9} \, Cm$. The electric potential due to the dipole at a point at a distance of $0.6 \, m$ from the centre of the dipole,situated on a line making an angle of $60^{\circ}$ with the dipole axis is $.........V$. (Given: $\frac{1}{4 \pi \epsilon_{0}} = 9 \times 10^{9} \, Nm^{2}/C^{2}$)

Three point charges of $3 \mu C, 4 \mu C$,and $5 \mu C$ are arranged at the three corners of a right-angled triangle $ABC$ as shown in the figure. The work done in moving the charges at $A$ and $C$,so that the three charges are located at the three corners of an equilateral triangle of side $3 \text{ cm}$ is (in $J$)

$A$ moving positive charge approaches a negative charge. What will happen to the potential energy of the system?

Two opposite and equal charges each of magnitude $4 \times 10^{-8} \text{ C}$ form a dipole. Their separation is $2 \times 10^{-2} \text{ cm}$. When this dipole is placed in an external electric field of $4 \times 10^8 \text{ NC}^{-1}$,the value of maximum torque and the work done in rotating it through $180^{\circ}$ respectively will be:

Three point charges $q, q$ and $-2q$ are placed at the corners of an equilateral triangle of side $L$. Calculate the work done by an external force in moving all the charges far apart without acceleration.