$A$ strong magnetic field is applied on a stationary electron. Then,the electron

The figure shows three situations when an electron with velocity $\vec v$ travels through a uniform magnetic field $\vec B$. In each case,what is the direction of the magnetic force on the electron?

$A$ proton, a deuteron (nucleus of ${ }_1 H^2$) and an $\alpha$-particle with the same kinetic energy enter a region of uniform magnetic field moving at right angles to the field. The ratio of the radii of their circular paths is:

$A$ charge $+Q$ is moving upwards vertically. It enters a magnetic field directed to the north. The force on the charge will be towards

An electron is projected along the axis of a circular conductor carrying current $I$. The electron will experience:

$A$ 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?