Physics 9702 · AS & A Level · Force on a moving charge
Force on a moving charge — practice question
Positive ions move through a vacuum as a thin beam. They enter a region where the magnetic field has uniform flux density $B$ and are bent into a semi-circular path, as shown in Fig. 5.1. The ions, moving at speed $1.40 \times 10^{5}\,\text{m s}^{-1}$, are recorded by a fixed detector when the diameter of the arc in the magnetic field is $12.8\,\text{cm}$.
(a)[1]
Using Fig. 5.1, state the direction of the magnetic field.
(b)[3]
The ions have mass $20\,\text{u}$ and charge $+1.6 \times 10^{-19}\,\text{C}$. Show that the magnetic flux density is $0.454\,\text{T}$. Explain your working.
(c)
The beam also contains ions of mass $22\,\text{u}$ that have the same charge and speed as the ions in (b).
(c(i))[1]
On Fig. 5.1, sketch the path followed by these ions in the magnetic field of magnetic flux density $0.454\,\text{T}$.
(c(ii))[2]
The magnetic flux density is adjusted so that these ions can be detected at the fixed detector. Calculate this new magnetic flux density.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Into the plane of the paper.” …