Explain what is meant by a field of force.
State the type of field, or fields, that will give rise to a force acting on a moving uncharged particle.
State the type of field, or fields, that will give rise to a force acting on a stationary charged particle.
State the type of field, or fields, that will give rise to a force acting on a charged particle moving at an angle to the field or fields.
An electron, mass $m$ and charge $-q$, is travelling at speed $v$ in a vacuum. It enters a region of uniform magnetic field of flux density $B$, as illustrated in Fig. 7.1. Initially, the electron is moving at right-angles to the magnetic field direction. Explain why the electron's path in the magnetic field is an arc of a circle.
Derive an expression, in terms of the radius $r$ of the path, for the linear momentum of the electron. Show your working.