The charge on an $\alpha -$ particle is ........... units.

The increasing order (lowest first) for the values of $e/m$ (charge/mass) for:

Electrons in a cathode ray tube have been emitted with a velocity of $1000 \, m \, s^{-1}$. The number of following statements which is/are true about the emitted radiation is
Given : $h = 6 \times 10^{-34} \, Js$,$m_{e} = 9 \times 10^{-31} \, kg$.
$(A)$ The de Broglie wavelength of the electron emitted is $666.67 \, nm$.
$(B)$ The characteristic of electrons emitted depend upon the material of the electrodes of the cathode ray tube.
$(C)$ The cathode rays start from cathode and move towards anode.
$(D)$ The nature of the emitted electrons depends on the nature of the gas present in cathode ray tube.

The ratio of specific charge of a proton and an $\alpha$-particle is

An elementary particle is:

The relationship between the radius of the nucleus $(R)$ and the mass number $(A)$ is given by .......