A charged particle moves with velocity $v$ in a uniform magnetic field $\overrightarrow B $. The magnetic force experienced by the particle is
Always zero
Zero, if $\overrightarrow B $ and $\overrightarrow {v\,} $ are parallel
Zero, if $\overrightarrow B $ and $\overrightarrow {v\,} $ are perpendicular
Never zero
An ion beam of specific charge $5 \times 10^7$ $coulomb/kg$ enter a uniform magnetic field of $4 \times 10^{-2}\, tesla$ with a velocity $2 \times 10^5\, m/s$ perpendicularly. The radius of the circular path of ions in meter will be
An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy. Which of the following is true
If a proton is projected in a direction perpendicular to a uniform magnetic field with velocity $v$ and an electron is projected along the lines of force, what will happen to proton and electron
A beam of well collimated cathode rays travelling with a speed of $5 \times {10^6}\,m{s^{ - 1}}$ enter a region of mutually perpendicular electric and magnetic fields and emerge undeviated from this region. If $| B |=0.02\; T$, the magnitude of the electric field is
Proton, deuteron and alpha particle of same kinetic energy are moving in circular trajectories in a constant magnetic field. The radii of proton, deuteron and alpha particle are respectively $r_p, r_d$ and $r_{\alpha}$ Which one of the following relation is correct?