Physics 9702 · AS & A Level · Force on a moving charge
Force on a moving charge — practice question
An electron is moving through a vacuum at a speed of $3.4 \times 10^7\,\text{m s}^{-1}$. It then enters a region of uniform magnetic field with flux density $3.2\,$mT, as shown in Fig. 8.1. The electron initially travels at an angle of $30^\circ$ to the direction of the magnetic field.
(a(i))[1]
As the electron enters the magnetic field, its velocity component $v_N$ at right angles to the field direction makes the electron start to move in a circular path. Calculate $v_N$.
(a(ii))[3]
Calculate the radius of the circular path.
(b)[1]
State the magnitude of the force, if any, acting on the electron in the magnetic field because of the component of its velocity parallel to the direction of the field.
(c)[1]
Use the information from (a) and (b) to describe the electron’s resultant path in the magnetic field.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$v_N = 3.4 \times 10^7 \sin 30^\circ = 1.7 \times 10^7\,\text{m s}^{-1}$” …