If a charged particle enters perpendicularly in a uniform magnetic field,then:

Two infinitely long straight wires $A$ and $B$,each carrying current $I$,are placed on the $x$ and $y$-axes,respectively. The current in wires $A$ and $B$ flows along $-\hat{i}$ and $\hat{j}$ directions,respectively. The force on a charged particle having charge $q$,moving from position $r = d(\hat{i} + \hat{j})$ with velocity $v = v\hat{i}$ is:

$A$ magnetic field:

An electron of mass $m$ and charge $q$ is moving with a speed $v$ in a circular path of radius $r$ perpendicular to a uniform magnetic field of intensity $B$. If the speed of the electron is doubled and the magnetic field is halved,what will be the radius of the resulting path?

The distance between two plates is $1 \ cm$ and the potential difference is $1000 \ V$. $A$ magnetic field $B = 1 \ T$ is applied. If an electron passes through without any deflection,what will be its velocity?

Two ions having masses in the ratio $1: 1$ and charges $1: 2$ are projected into a uniform magnetic field perpendicular to the field with speeds in the ratio $2: 3$. The ratio of the radii of circular paths along which the two particles move is :