In the figure shown, $A$ is a fixed charge and $B$ (of mass $m$) is given a velocity $v$ perpendicular to line $AB.$ At this moment, the radius of curvature of the resultant path of $B$ is

A mass $m=20 \mathrm{g}$has a charge $q=3.0 \mathrm{mC}.$ It moves with a velocity of $20 \mathrm{m} {\mathrm{s}}^{-1}$and enters a region of an electric field $80 \mathrm{N} {\mathrm{C}}^{-1}$in the same direction as the velocity of the mass. The velocity of the mass after $3 \mathrm{s}$ in this region is

Four charges are placed on corners of a square as shown in the figure having a side of $5 \mathrm{cm}$. If $Q=1 \mathrm{\mu C}$, then electric field intensity at the center of the square will be

Three identical positive point charges, as shown, are placed at the vertices of an isosceles right-angled triangle. Which of the numbered vectors coincides in direction with the electric field at the mid-point $M$of the hypotenuse?

An electron is projected, as shown in the figure, with kinetic energy $K$ and at an angle $\text{θ}=45°$ between the two charged plates. What should be the magnitude of the electric field between the plates so that the electron just fails to strike the upper charged plate?