Explain the meaning of a magnetic field.
The particle has mass $m$, charge $+q$ and speed $v$. It enters a uniform magnetic field of flux density $B$ and, on entry, it is moving perpendicular to the field, as shown in Fig. 8.1. The magnetic field points into the plane of the paper and is perpendicular to it. On Fig. 8.1, sketch the particle’s path through the magnetic-field region and beyond it.
A force acts on the particle, so it accelerates. Explain why the speed of the particle on leaving the magnetic field is $v$.
In part (b), the particle loses an electron so that its charge changes to $+2q$. Its mass change is negligible. Determine, in terms of $v$, the initial speed of the particle needed for its path through the magnetic field to remain unchanged. Show your working.