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?

An ellipsoidal cavity is carved within a perfect conductor. $A$ positive charge $q$ is placed at the centre of the cavity. The points $A$ and $B$ are on the cavity surface as shown in the figure. Then

Two equal charges $q$ are placed at a distance of $2a$ on the $x$-axis. A third charge $q$ of mass $m$ is placed at the midpoint between them. If this charge is displaced by a small distance $x$ from the equilibrium position, the particle will:

Four charges $2C, -3C, -4C$ and $5C$ are placed at the corners of a square. Which of the following statements is true for the point of intersection of the diagonals?

An inclined plane making an angle $30^{\circ}$ with the horizontal is placed in a uniform horizontal electric field of $100 \ Vm^{-1}$ as shown in the figure. $A$ small block of mass $1 \ kg$ and charge $0.01 \ C$ is allowed to slide down from rest from a height $h=1 \ m$. If the coefficient of friction is $0.2$,then the acceleration of the block is nearly,
(Acceleration due to gravity,$g=10 \ ms^{-2}$) (in $ms^{-2}$)

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