While doing his experiment, Millikan one day observed the following charges on a single drop

$(i)$ $6.563 \times {10^{ - 19}}C$       $  (ii)$ $8.204 \times {10^{ - 19}}C$

$(iii)$ $11.50 \times {10^{ - 19}}C$       $ (iv)$ $13.13 \times {10^{ - 19}}C$

$(v)$ $16.48 \times {10^{ - 19}}C$       $ (vi)$ $18.09 \times {10^{ - 19}}C$

From this data the value of the elementary charge $(e)$ was found to be

In a parabola spectrograph, the velocities of four positive ions $P,Q,R$ and $S$ are $v_1$, $v_2$, $v_3$ and $v_4$ respectively

An electron gun with its collector at a potential of $100\; V$ fires out electrons in a spherical bulb containing hydrogen gas at low pressure $(\sim 10^{-2} \;mm$ of $Hg$ . A magnetic field of $2.83 \times 10^{-4}\; T$ curves the path of the electrons in a circular orbit of radius $12.0 \;cm .$ (The path can be viewed because the gas tons in the path focus the beam by attracting electrons, and emitting light by electron capture; this method is known as the 'fine beam tube' method.) Determine $e / m$ from the data.

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

$1$ $J$ is equal to how many electron volt? 

Particle nature and wave nature of electromagnetic waves and electrons can be shown by