Explain what the term field of force means.
State the type of field, or fields, that will produce a force on a moving uncharged particle.
State the type of field, or fields, that will produce a force on a stationary charged particle.
State the type of field, or fields, that will produce a force 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 shown in Fig. 7.1. At first, the electron moves at right-angles to the direction of the magnetic field. Explain why the path of the electron in the magnetic field is the arc of a circle.
Derive an expression, in terms of the radius $r$ of the path, for the linear momentum of the electron. Show how you work it out.