A beam of electrons is moving with constant velocity in a region having electric and magnetic fields

Question

A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength $20 \mathrm{~V} \mathrm{~m}^{-1}$ and 0.5 T at right angles to the direction of motion of the electrons. What is the velocity of the electrons?\

Professor PC Thomas Classes · Answer

(d): Electric field $(E)=20 \mathrm{~V} / \mathrm{m}$ and magnetic field $(B)=0.5 \mathrm{~T}$.\ The force on electron in a magnetic field $=e v B$\ Force on electron in an electric field $=e E$\ Since the electron is moving with constant velocity, therefore the resultant force on electron is zero.\ i.e., $e E=e v B \Rightarrow v=E / B=20 / 0.5=40 \mathrm{~m} \mathrm{~s}^{-1}$\