Explain how a uniform magnetic field together with a uniform electric field can be used as a velocity selector for charged particles.
Particles with mass $m$ and charge $+1.6 \times 10^{-19}\,\text{C}$ pass through a velocity selector. They then move into a region of uniform magnetic field with magnetic flux density $94\,\text{mT}$ and speed $3.4 \times 10^{4}\,\text{m s}^{-1}$, as shown in Fig. 8.1. The uniform magnetic field is directed into the page and is perpendicular to the direction of motion of the particles. The particles travel in a vacuum along a circular arc of diameter $15.0\,\text{cm}$. Show that the mass of one of the particles is $20\,\text{u}$.
On Fig. 8.1, sketch the path in the uniform magnetic field for a particle of mass $22\,\text{u}$ with the same charge and speed as the particle in (b).