An elementary particle is:

Which particle leaves no track in a Wilson cloud chamber?

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.

Which of the following statements regarding cathode rays is incorrect?

Proton was discovered by

When beryllium is bombarded with $\alpha$-particles,extremely penetrating radiations which cannot be deflected by electrical or magnetic field are given out. These are