If an electron enters a magnetic field with its velocity pointing in the same direction as the magnetic field,then

$A$ proton,a deuteron and an $\alpha$-particle having the same kinetic energy are moving in circular trajectories in a constant magnetic field. If ${r_p}$,${r_d}$ and ${r_\alpha}$ denote respectively the radii of the trajectories of these particles,then:

$A$ homogeneous electric field $\vec{E}$ and a uniform magnetic field $\vec{B}$ are pointing in the same direction. $A$ proton is projected with its velocity parallel to $\vec{E}$. It will

Which particles will have the minimum frequency of revolution when projected with the same velocity perpendicular to a magnetic field?

When a positively charged particle enters a uniform magnetic field with uniform velocity,its trajectory can be:
$(1)$ a straight line
$(2)$ a circle
$(3)$ a helix

Two charged particles,having the same kinetic energy,are allowed to pass through a uniform magnetic field perpendicular to the direction of motion. If the ratio of the radii of their circular paths is $6:5$ and their respective masses ratio is $9:4$,then the ratio of their charges will be.