In Thomson experiment of finding $e/m$ for electrons, beam of electron is replaced by that of muons (particle with same charge as of electrons but mass $208$ times that of electrons). No deflection condition in this case satisfied if
$B$ is increased $208$ times
$E$ is increased $208$ times
$B$ is increased $14.4$ times
None of these
When electron beam passes through an electric field, they gain kinetic energy. If the same beam passes through magnetic field, then
In an electron gun the control grid is given a negative potential relative to cathode in order to
An electron is moving with constant velocity along $x - $ axis. If a uniform electric field is applied along $y - $ axis, then its path in the $x - y$ plane will be
The colour of the positive column in a gas discharge tube depends on
An oxide coated filament is useful in vacuum tubes because essentially