NCERT Solutions for Class 12 Physics Chapter 11

NCERT Solutions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter Exercises Solutions and Additional Exercises Solutions to study online without downloading or download Apps and Solutions based on updated NCERT Books for 2019-20.


Class:12
Subject:Physics
Chapter 11:Dual Nature of Radiation and Matter

NCERT Solutions for Class 12 Physics Chapter 11

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12 Physics Chapter 11 Exercises

NCERT Solutions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter exercises are given below to use it online. Click here to see the Additional Exercises questions of this chapter or go to 12 Physics main page.
NCERT Solutions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter
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12 Physics Chapter 11 Additional Exercises

NCERT Solutions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter additional exercises are given below to use it online. Click here to see Exercises Questions or move to Top of the page or go to 12 Physics main page.
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Previous Chapter: Wave Optics
Next Chapter: Atom



Questions for Practice
  1. What is the stopping potential applied to a photocell, in which electrons with a maximum kinetic energy of 5.6 eV are emitted.
  2. If the amount of a radioactive substance is increased four times then how many times will the number of atoms disintegrating per unit time be increased?
  3. Why does only a slow neutron (.03eV energy) cause the fission in the uranium nucleus and not the fast one?
  4. In Bohr’s atomic model, the potential energy is negative and has a magnitude greater than the kinetic energy, what does this imply?
  5. The half life of a radioactive element A is same as the mean life time of another radioactive element B. Initially, both have same number of atoms. B decay faster than A. Why?



Try These
  • The work function of the following metal is given Na = 2.75 eV, K = 2.3 eV, Mo = 4.14 eV, Ni = 5.15 eV which of these metal will not give a photoelectric emission for radiation of wave length 3300 A0 from a laser
    source placed at 1m away from the metal. What happens if the laser is brought nearer and placed 50 cm away.
  • Why photo-electrons ejected from a metal surface have different kinetic energies although the frequency of incident photons are same?
  • Define distance of the closest approach. An alpha-particle of kinetic energy ‘K’ is bombarded on a thin gold foil. The distance of the closet approach is ‘r’. What will be the distance of closest approach for an alpha-particle of double the kinetic energy?
  • If the total number of neutrons and protons in a nuclear reaction is conserved how then is the energy absorbed or evolved in the reaction?
  • Particle of mass M at rest decays into two particles of masses m1 and m2 having velocities V1 and V2 respectively. Find the ratio of de-Broglie Wavelengths of the two particles.

In an experiment on photoelectric effect, the slope of the cut-off voltage versus frequency of incident light is found to be 4.12 × 10^−15 V s. Calculate the value of Planck’s constant.

The slope of the cut-off voltage (V) versus frequency (ν) of an incident light is given as: V/v=4.12×〖10〗^(-15) Vs
V is related to frequency by the equation
hv = eV
Where, e = Charge on an electron = 1.6 × 10^−19 C and
h = Planck’s constant
Therefore,
h = e×V/v
= 1.6×〖10〗^(-19) × 4.12 ×〖10〗^(-15)
= 6.592 ×〖10〗^(-34) Js
Hence, the value of Plank’s constant is 6.592×〖10〗^(-34) Js.

Show that the wavelength of electromagnetic radiation is equal to the de Broglie wavelength of its quantum (photon).

The momentum of a photon having energy (hν) is given as: p=hv/c=h/λ
⇒λ=h/p … (i)
Where, λ = Wavelength of the electromagnetic radiation
c = Speed of light
h = Planck’s constant
De Broglie wavelength of the photon is given as: λ=h/mv
But p=mv, therefore
λ=h/p … (ii)
Where, m = Mass of the photon
v = Velocity of the photon
Hence, it can be inferred from equations (i) and (ii) that the wavelength of the electromagnetic radiation is equal to the de Broglie wavelength of the photon.

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?

Quarks inside protons and neutrons carry fractional charges. This is because nuclear force increases extremely if they are pulled apart. Therefore, fractional charges may exist in nature; observable charges are still the integral multiple of an electrical charge.

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

At atmospheric pressure, the ions of gases have no chance of reaching their respective electrons because of collision and recombination with other gas molecules. Hence, gases are insulators at atmospheric pressure. At low pressures, ions have a chance of reaching their respective electrodes and constitute a current. Hence, they conduct electricity at these pressures.

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?

The work function of a metal is the minimum energy required for a conduction electron to get out of the metal surface. All the electrons in an atom do not have the same energy level. When a ray having some photon energy is incident on a metal surface, the electrons come out from different levels with different energies. Hence, these emitted electrons show different energy distributions.