What is the change in kinetic energy of an $\alpha$-particle when it moves from a point at $70\ V$ to a point at $50\ V$?

Equal charges are given to two spheres of different radii. The potential will

Charges $+q$ and $-q$ are placed at points $A$ and $B$ respectively,which are a distance $2L$ apart. $C$ is the midpoint between $A$ and $B$. The work done in moving a charge $+Q$ along the semicircle $CRD$ is

As shown in the figure, charges $+q, +q, -q$ and $-q$ are placed on the vertices of a square, each side length is $2l$. The electric potential at the mid-point '$A$' of the charges $+q$ and $+q$ is . . . . . . .

Three concentric spherical metallic shells $X$,$Y$,and $Z$ of radii $a$,$b$,and $c$ respectively $[a < b < c]$ have surface charge densities $\sigma$,$-\sigma$,and $\sigma$,respectively. The shells $X$ and $Z$ are at the same potential. If the radii of $X$ and $Y$ are $2\,cm$ and $3\,cm$,respectively,then the radius of shell $Z$ is $......\,cm$.

The linear charge density on a dielectric ring of radius $R$ varies with $\theta$ as $\lambda = \lambda_0 \cos(\theta/2)$,where $\lambda_0$ is a constant. Find the potential at the centre $O$ of the ring.