The cathode rays have particle nature because of the fact that

  • A

    They can propagate in vacuum

  • B

    They are deflected by electric and magnetic fields

  • C

    They produced fluorescence

  • D

    They cast shadows

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Answer the following questions:

$(a)$ guarks inside protons and neutrons are thought to carry fractional charges $[(+2 / 3) e ; (-1 / 3) e] .$ Why do they not show up in Millikan's oil-drop experiment?

$(b)$ What is so special about the combination $e / m ?$ Why do we not simply talk of $e$ and $m$ separately?

$(c)$ Why should gases be insulators at ordinary pressures and start conducting at very low pressures?

$(d)$ Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?

$(e)$ The energy and momentum of an electron are related to the frequency and wavelength of the assoctated matter wave by the relations:

$E=h v, p=\frac{h}{\lambda}$

But while the value of $\lambda$ is physically significant, the value of $v$ (and therefore, the value of the phase speed $v \lambda$ ) has no physical significance. Why?