An infinite long cylinder of radius $R$ has a cylindrical cavity of radius $R/2$ just touching its surface. The region inside the cylinder is filled with uniform charge density $\rho$ except in the cavity. A charge particle of charge $q$ and mass $\mathrm{m}$ is thrown from point $A$ in the cavity. Find the minimum velocity u required at $A$ for it to reach point $B$. $AB$ is perpendicular to the diameter of the cavity passing through the axis of the cylinder.

Three charged particles $\text{A}, \text{B}$ and $\text{C}$ with charges $-4q,2q$ and $-2q$ are present on the circumference of a circle of radius $d.$ The charged particles $\text{A},\text{C}$ and centre $\text{O}$ of the circle formed an equilateral triangle as shown in the figure. The electric field at the point $\text{O}$ is

Which of the following is a landlocked country?

Two charges of equal magnitudes and at a distance $r$ exert a force $F$ on each other. If the charges are halved and distance between them is doubled, then the new force acting on each charge is

What will be the direction of the magnetic field at the very bottom point of a horizontal power line, where the current flows from east to west when viewed from the west end?

The flow of _____ is anti–clockwise in the given circuit: