Physics 9702 · AS & A Level · Force on a moving charge
Force on a moving charge — practice question
A particle of mass $m$ and charge $+q$ moves through a vacuum at speed $v$. Its initial motion is parallel to the plane of two horizontal charged metal plates, as shown in Fig. 6.1. The uniform electric field between the plates has magnitude $2.8 \times 10^{4}\,\text{V m}^{-1}$ and is zero outside the plates. The particle goes between the plates and then emerges beyond them, as illustrated in Fig. 6.1.
(a)[1]
Explain why the particle’s path in the electric field is not a circular arc.
(b)
A uniform magnetic field is then set up in the region between the metal plates. The field strength is adjusted so that the positively charged particle passes undeviated between the plates, as shown in Fig. 6.2.
(b(i))[2]
State and explain the magnetic field’s direction.
(b(ii))[3]
The particle moves at speed $4.7 \times 10^{5}\,\text{m s}^{-1}$. Calculate the magnitude of the magnetic flux density. Explain your working.
(c)
The particle in (b) has mass $m$, charge $+q$ and speed $v$. Without any further calculation, state the effect, if any, on the path of a particle that has:
(c(i))[1]
having mass $m$, charge $-q$ and speed $v$.
(c(ii))[1]
having mass $m$, charge $+q$ and speed $2v$.
(c(iii))[1]
having mass $2m$, charge $+q$ and speed $v$.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Constant speed parallel to the plate OR acceleration at right angles to the plate” …