$A$ tiny $0.50\, g$ ball carries a charge of magnitude $10\, \mu C$. It is suspended by a thread in a downward electric field of intensity $300\, N/C$. If the charge on the ball is positive,then the tension in the string is

Why is an electric force conservative?

$A$ circular wire loop of radius $10 \ cm$ carries a total charge of $10^{-5} \ C$ distributed uniformly over its length. $A$ small length of $3.14 \times 10^{-6} \ m$ of wire is cut off. The magnitude of the electric field at the centre due to the remaining wire is:
(Assume $\frac{1}{4 \pi \epsilon_{0}} = 9 \times 10^{9} \ SI$ units) (in $N \ C^{-1}$)

$A$ conducting sphere of radius $10 \, cm$ has an unknown charge. If the electric field at a distance $20 \, cm$ from the centre of the sphere is $1.2 \times 10^3 \, N \, C^{-1}$ and points radially inwards,the net charge on the sphere is:

Four charges $+q, +2q, +q$ and $-2q$ are placed at the corners $A, B, C$ and $D$ of a square respectively. The force on a unit positive charge kept at the centre $O$ is

$A$ half ring of radius $R$ has a linear charge density of $\lambda$. The electric force on a $1\, C$ charge placed at the centre is