Physics 9702 · AS & A Level · Force on a moving charge
Force on a moving charge — practice question
A parallel beam of negatively-charged particles moves through a vacuum with speed $v$. They enter a region containing a uniform magnetic field with flux density $930\,\mu\text{T}$. At first, the particles move at right-angles to the magnetic field. Fig. 7.1 shows the path of one particle. In the magnetic field, the negatively-charged particles travel along a curved path with radius $7.9\,\text{cm}$. A uniform electric field is then introduced in the same region as the magnetic field. When the electric field strength is $12\,\text{kV m}^{-1}$, the particles pass through the region of fields without any deflection.
(a)[1]
On Fig. 7.1, use an arrow to show the direction of the electric field.
(b(i))[3]
Calculate, for the negatively-charged particles, the speed $v$.
(b(ii))[3]
Calculate, for the negatively-charged particles, the ratio $\frac{\text{charge}}{\text{mass}}$.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Arrow directed up the page” …