$A$ particle of mass $m$,charge $Q$,and kinetic energy $K$ enters a transverse uniform magnetic field of induction $B$. After $3$ $seconds$,the kinetic energy of the particle will be .......$K$.

An electron is moving along the positive $x$-axis. $A$ uniform electric field exists towards the negative $y$-axis. What should be the direction of a magnetic field of suitable magnitude so that the net force on the electron is zero?

The ratio of time periods of $\alpha$-particle and proton moving on circular path in a uniform magnetic field is . . . . . . .

When a charged particle enters a uniform magnetic field,its kinetic energy

$A$ proton beam enters a magnetic field of $10^{-4} \ T$ normally. Given the specific charge $\frac{q}{m} = 10^{11} \ C/kg$ and velocity $v = 10^7 \ m/s$,what is the radius of the circular path described by the beam in meters?

An electron is moving in a circle of radius $r$ in a magnetic field $B$. Suddenly,the field is reduced to $B/2$. The radius of the circular path is