An electron of mass $m = 9.1 \cdot 10^{-31}$ kg and charge $q = 1.6 \cdot 10^{-19}$ C enters a magnetic field $B = 0.01$ T with speed $v = 2 \cdot 10^6$ m/s perpendicular to the induction lines. Find the period of revolution of the electron.
The radius and period of circular motion of a charge in a magnetic field:
$$T = \frac{2\pi m}{qB}$$
$$T = \frac{2\pi \cdot 9.1 \cdot 10^{-31}}{1.6 \cdot 10^{-19} \cdot 0.01} = \frac{5.72 \cdot 10^{-30}}{1.6 \cdot 10^{-21}} \approx 3.57 \cdot 10^{-9} \text{ s}$$
$T \approx 3.57 \cdot 10^{-9}$ s