$n$ 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

In Milikan’s experiment, an oil drop having charge $q$ gets stationary on applying a potential difference $V$ in between two plates separated by a distance $‘d’$. The weight of the drop is

A charge of magnitude $3e$ and mass $2m$ is moving in an electric field $\overrightarrow E .$ The acceleration imparted to the charge is

In a Thomson set-up for the determination of e/m, electrons accelerated by $2.5$ $kV$ enter the region of crossed electric and magnetic fields of strengths $3.6 \times {10^4}V{m^{ - 1}}$ and $1.2 \times {10^{ - 3}}T$ respectively and go through undeflected. The measured value of $e/m$ of the electron is equal to

The charge on electron was discovered by

Cathode rays are produced when the pressure is of the order of