Halliday, Resnick & Walker — Magnetic Fields: Problem 12

12 A source injects an electron of speed \( v = 1.2 \times 10^7 \text{ m/s} \) into a uniform magnetic field of magnitude \( B = 1.0 \times 10^{-3} \text{ T} \). The velocity of the electron makes an angle \( \theta = 10^\circ \) with the direction of the magnetic field. Find the distance \( d \) from the point of injection at which the electron next crosses the field line that passes through the injection point.