The time period of a block of mass $m$ suspended from the upper plate of a parallel plate capacitor by a spring of stiffness $k$ is $T$ when the block is uncharged. If a charge $q$ is given to the block,what will be the new time period of oscillation?

Assertion: Consider two identical charges placed at a distance $2d$ apart along the $x-$axis. The equilibrium of a positive test charge placed at the point $O$ midway between them is stable for displacements along the $x-$axis.
Reason: The net force on the test charge at point $O$ is zero.

The unit of electric field is not equivalent to

Charges are placed on the vertices of a square as shown. Let $\vec E$ be the electric field and $V$ be the potential at the centre. If the charges on $A$ and $B$ are interchanged with those on $D$ and $C$ respectively,then

The figure represents a crystal unit of cesium chloride, $CsCl$. The cesium atoms, represented by open circles, are situated at the corners of a cube of side $0.40 \, nm$, whereas a $Cl$ atom is situated at the centre of the cube. The $Cs$ atoms are deficient in one electron while the $Cl$ atom carries an excess electron.
$(i)$ What is the net electric field on the $Cl$ atom due to eight $Cs$ atoms?
$(ii)$ Suppose that the $Cs$ atom at the corner $A$ is missing. What is the net force now on the $Cl$ atom due to the seven remaining $Cs$ atoms?

Two fixed charges $+4\,Q$ and $-Q$ are located at $A$ and $B$ respectively,with the distance $AB = 3\,m$.