Two protons move parallel to each other, keeping distance $r$ between them, both moving with same  velocity $\vec V\,$. Then the ratio of the electric and magnetic force of interaction between them is

Two very long, straight, parallel wires carry steady currents $I$ and $-I$ respectively. The distance  etween the wires is $d$. At a certain instant of time, a point charge $q$ is at a point equidistant from the two wires, in the plane of the wires. Its instantaneous velocity $v$ is perpendicular to the plane of wires. The magnitude of the force due to the magnetic field acting on the charge at this instant is

A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particle will

An electron is moving along the positive $x$-axis. If the uniform magnetic field is applied parallel to the negative $z$-axis. then

$A.$ The electron will experience magnetic force along positive $y$-axis

$B.$ The electron will experience magnetic force along negative $y$-axis

$C.$ The electron will not experience any force in magnetic field

$D.$ The electron will continue to move along the positive $x$-axis

$E.$ The electron will move along circular path in magnetic field

Choose the correct answer from the options given below:

Explain : Velocity selector.

A charge $q$ moves in a region where electric field and magnetic field both exist, then force on it is