Physics 9702 · AS & A Level · Force on a moving charge
Force on a moving charge — practice question
A Hall probe made from a thin slice of semiconducting material is inserted into a uniform magnetic field of flux density $B$. As shown in Fig. 7.1, the broad faces of the slice are at right angles to the magnetic field. The thickness $x$ of the slice is $1.8\,\text{mm}$. The number density of charge carriers in the semiconducting material is $1.5 \times 10^{16}\,\text{m}^{-3}$. A steady current of $5.4\,\text{A}$ is driven through the slice between the shaded faces. The Hall voltage $V_H$ developed across terminals $PQ$ is measured. Fig. 7.2 shows how $B$ varies with time $t$.
(a(i))[1]
Show that, when $B$ is $4.0 \times 10^{-6}\,\text{T}$, the magnitude of $V_H$ is $5.0\,\text{V}$.
(a(ii))[3]
On Fig. 7.3, sketch how $V_H$ varies with $t$ for $t = 0$ to $t = 0.080\,\text{s}$.
(b(i))[3]
Show that the size of the electromotive force $E$ at time $t = 0.010\,\text{s}$ is $2.0 \times 10^{-4}\,\text{V}$.
(b(ii))[4]
On Fig. 7.4, sketch how $E$ varies with $t$ between $t = 0$ and $t = 0.080\,\text{s}$.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Applying $V_H = \frac{BI}{ntq}$” …