Answer
Particle 3 has the greatest speed.
Work Step by Step
We know that a charged particle moves in a circular path, if the velocity $(\vec v)$ of the particle is perpendicular to a uniform magnetic field $(\vec B)$. In that case, the radius $(r)$ of the circle is given by the formula: $r=\frac{mv}{|q|B}$, where $m$ is the mass of the particle and $q$ is the charge of the particle. This result shows that the radius of the circular path is directly proportional to the velocity of the charge particle, when $m$, $q$ and $B$ remain constant. In Figure 21.13 (a), particle 3 has greater radius of circular path than that of others. Therefore particle 3 has the greatest speed.
