Two positive point charges of unequal magnitude are placed at a certain distance apart. A small positive test charge is placed at null point, then
The test charge is in unstable equilibrium
The test charge is in stable equilibrium
The test charge is in neutral equilibrium
The test charge is not in equilibrium
Point charges $ + 4q,\, - q$ and $ + 4q$ are kept on the $x - $axis at points $x = 0,\,x = a$ and $x = 2a$ respectively, then
An infinite number of point charges, each carrying $1 \,\mu C$ charge, are placed along the y-axis at $y=1\, m , 2\, m , 4 \,m , 8\, m \ldots \ldots \ldots \ldots \ldots$
The total force on a $1 \,C$ point charge, placed at the origin, is $x \times 10^{3}\, N$. The value of $x$, to the nearest integer, is .........
[Take $\left.\frac{1}{4 \pi \epsilon_{0}}=9 \times 10^{9} \,Nm ^{2} / C ^{2}\right]$
A charge $q$ is placed at the centre of the line joining two equal charges $Q$. The system of the three charges will be in equilibrium, if $q$ is equal to
Four charges are arranged at the corners of a square $ABCD$, as shown. The force on a $+ve$ charge kept at the centre of the square is
Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle of $30^{\circ}$ with each other. When suspended in a liquid of density $0.8 \;g\, cm ^{-3}$, the angle remains the same. If density of the material of the sphere is $1.6\; g \,cm ^{-3}$, the dielectric constant of the liquid is