Answer the following questions: (a) Quarks inside protons and neutrons are thought to carryfractional charges [(+2/3)e ; (–1/3)e]. Why do they not show upin Millikan’s oil-drop experiment? (b) What is so special about the combination e/m? Why do we notsimply talk of e and m separately? (c) Why should gases be insulators at ordinary pressures and startconducting at very low pressures? (d) Every metal has a definite work function. Why do allphotoelectrons not come out with the same energy if incidentradiation is monochromatic? Why is there an energy distributionof photoelectrons? (e) The energy and momentum of an electron are related to thefrequency and wavelength of the associated matter wave by therelations:E = h ν, p = λhBut while the value of λ is physically significant, the value of ν(and therefore, the value of the phase speed ν λ) has no physicalsignificance. Why?
a)
The fractional charges are ( + 2 3 ) e , ( − − 1 3 ) e to carry quarks inside the protons and neutrons respectively and when the protons and neutrons are pulled apart then the nuclear force will be increased extremely due to this quarks carry fractional charges inside protons and neutrons. So the fractional charges may exist in nature but the observational charges will be still the integral multiple of an electrical charge.
Thus, the quarks do not show up in Millikan’s oil drop experiment.
b)
The velocity in electric field is given as,
υ = 2 V ( e m )
The velocity in magnetic field is given as,
υ = B r ( e m )
Where, the velocity is υ , the electric charge is e , the mass is m , the potential is V , the radius is r and the magnetic field is B .
From the above two relations it can be observed that the dynamics of an electron is determined by the ratio of e and m .
Therefore, we do not simply talk of e and m separately.
c)
At ordinary pressure, the number of ions and electrons produced by ionization are very high. So, the mean free path is less and there are frequent collisions with the gas molecules. Thus, there is very less chances for ions of gasses to reach their respective electrodes at atmospheric pressure and gases behave like an insulator.
At low pressure, the density of ions and electrons produced by ionization decreases. So, the mean free path becomes larger and they acquire sufficient energy under the effect of external high voltage to reach their respective electrodes and gases behave like a conductor.
d)
The minimum energy required for a conduction electron to get out from the metal surface will be the work function of a metal. So the energy level will not be same for all the electrons.
When a photon ray is incident on a metal surface then the electrons will come out from different levels with different energies.
Thus, the emitted electrons from the metal surface will show different energy distributions.
e)
The absolute value of energy of a particle is arbitrary within the additive constant. So the frequency that is associated with an electron has no direct physical significance and the wavelength will be significant.
The group speed is given as,
υ G = p m
Where, the momentum is p and the mass is m .
Thus, the quantity in the group speed has a physical meaning and the phase speed has no physical significance.
a)
The fractional charges are
Thus, the quarks do not show up in Millikan’s oil drop experiment.
b)
The velocity in electric field is given as,
The velocity in magnetic field is given as,
Where, the velocity is
From the above two relations it can be observed that the dynamics of an electron is determined by the ratio of
Therefore, we do not simply talk of
c)
At ordinary pressure, the number of ions and electrons produced by ionization are very high. So, the mean free path is less and there are frequent collisions with the gas molecules. Thus, there is very less chances for ions of gasses to reach their respective electrodes at atmospheric pressure and gases behave like an insulator.
At low pressure, the density of ions and electrons produced by ionization decreases. So, the mean free path becomes larger and they acquire sufficient energy under the effect of external high voltage to reach their respective electrodes and gases behave like a conductor.
d)
The minimum energy required for a conduction electron to get out from the metal surface will be the work function of a metal. So the energy level will not be same for all the electrons.
When a photon ray is incident on a metal surface then the electrons will come out from different levels with different energies.
Thus, the emitted electrons from the metal surface will show different energy distributions.
e)
The absolute value of energy of a particle is arbitrary within the additive constant. So the frequency that is associated with an electron has no direct physical significance and the wavelength will be significant.
The group speed is given as,
Where, the momentum is
Thus, the quantity in the group speed has a physical meaning and the phase speed has no physical significance.
