A particle of mass $m$ and charge $q$ moves with a constant velocity $v$ along the positive $x$ direction. It enters a region containing a uniform magnetic field $B$ directed along the negative $z$ direction, extending from $x = a$ to $x = b$. The minimum value of $v$ required so that the particle can just enter the region $x > b$ is

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

A charge $Q$ moves parallel to a very long straight wire carrying a current $l$ as shown. The force on the charge is

A charged particle is released from rest in a region of steady uniform electric and magnetic fields which are parallel to each other the particle will move in a

Give features of force on charge particle inside magnetic field.

In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential $V$ and then made to describe semicircular paths of radius $R$ using a magnetic field $B$. If $V$ and $B$ are kept constant, the ratio $\left( {\frac{{{\text{charge on the ion}}}}{{{\text{mass of the ion}}}}} \right)$ will be proportional to