Q37 of 43 Page 409

Answer the following question:

The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations:



But while the value of λ is physically significant, the value of ν (and therefore, the value of the phase speed ν λ) has no physical significance. Why?

We understand that momentum and wavelength of photons have physical significance as it is evident from X-diffraction crystallography. But Energy of photon which is related to the frequency is arbitrary to within an additive constant, hence absolute value of frequency has no physical significance.


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37

Answer the following question:

Quarks 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?

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Answer the following question:

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

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Answer the following question:

Why should gases be insulators at ordinary pressures and start conducting at very low pressures?

 37

Answer the following question:

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?