Order of q/m ratio of proton, $\alpha $ -particle and electron is
$e > p > \alpha $
$p > \alpha > e$
$e > \alpha > p$
None of these
$n$ Millikan oil drop experiment, a charged drop of mass $1.8 \times {10^{ - 14}}kg $ is stationary between its plates. The distance between its plates is $0.90 cm$ and potential difference is $2.0$ kilo volts. The number of electrons on the drop is
Which one of the following devices makes use of the electrons to strike certain substances to produce fluorescence
Three particles having their charges in the ratio of $1 : 3 : 5$ produce the same spot on the screen in Thomson’s experiment. Their masses are in the ratio of
An electron of charge $‘e’$ coulomb passes through a potential difference of $V$ volts. Its energy in ‘joules’ will be
In an electron gun the control grid is given a negative potential relative to cathode in order to