Fill in the blanks:
$(i)$ $R. A. Millikan$ developed the ......... method to determine the charge of an electron.
$(ii)$ The positively charged particles in a modified cathode ray tube are called ............ .
$(iii)$ The smallest and lightest positive ion obtained from hydrogen is ........... .
$(iv)$ In the year $1932$,$Chadwick$ discovered ........... .

Alpha particles are $...$ times heavier (approximately) than neutrons.

Fill in the blanks given below:
$(i)$ The circular path around the nucleus in which electrons revolve at high speed is called ......... .
$(ii)$ Electrons and the nucleus are held together by ......... force.
$(iii)$ The number of $P^{+}$ in the nucleus and the sum of the number of $P^{+}$ and $n^{\circ}$ in the nucleus are represented by the symbols ...... and ......... respectively.
$(iv)$ The sum of the number of $P^{+}$ and $n^{\circ}$ in the nucleus is represented by the term ...... and the symbol .... respectively.

The mass of the proton is $1840$ times that of an electron. If a proton is accelerated through a potential difference of $1 \,kV$,the kinetic energy of the proton would be

Who determined the charge-to-mass ratio $(e/m_e)$ of an electron and how? Explain.

Identify the correct increasing order of $e/m$ ratio for the following particles: $n, p, e, \alpha$.