A beam of electrons is undeflected when it passes simultaneously through an electric field of 10 N/C perpendicular to its path and a magnetic field of 2 × 10^-4 T perpendicular both to its path and to the electric field. The speed of the electrons is approximately

Question

Quizplus · Accepted Answer

The electrons are undeflected when the electric force equals the magnetic force. Using the formula $E = vB$, where $E$ is the electric field, $v$ is the speed, and $B$ is the magnetic field, we find $v = \frac{E}{B} = \frac{10}{2 \times 10^{-4}} = 5 \times 10^4$ m/s.

A Beam of Electrons Is Undeflected When It Passes Simultaneously