An electron is moving in an electric field and a magnetic field. It will gain energy from:

When a charged particle moving with velocity $\vec{v}$ is subjected to a magnetic field of induction $\vec{B}$,the force on it is non-zero. This implies that

If a charged particle enters a uniform magnetic field normally with a certain velocity,then the time period of revolution of the particle

Explain: Velocity selector.

An electron gun is placed inside a long solenoid of radius $R$ on its axis. The solenoid has $n$ turns per unit length and carries a current $I$. The electron gun shoots an electron along the radius of the solenoid with speed $v$. If the electron does not hit the surface of the solenoid,the maximum possible value of $v$ is (all symbols have their standard meaning):

$A$ charged particle of charge $q$ and mass $m$ gets deflected through an angle $\theta$ upon passing through a square region of side $a$,which contains a uniform magnetic field $B$ normal to its plane. Assuming that the particle entered the square at right angles to one side,what is the speed of the particle?