Practice MCQ on Origin of Quantum Mechanics with Answers

**MCQ on Origin of Quantum Mechanics with Answers**

**Q1. A particle of rest mass m _{0} is moving uniformly in a straight line with relativistic velocity βc, where c is the velocity of light in vacuum and 0 < β < 1. The phase velocity of the de Broglie wave associated with the particle is :**

- (A) βc
- (B)
^{c}/_{β} - (C) c
- (D)
^{c}/β^{2}

**Q2. The black body spectrum of an object O _{1} is such that its radiant intensity (i.e. intensity per unit wavelength interval) is maximum at a wavelength of 200 nm. Another object O_{2} has the maximum radiant intensity at 600 nm. The ratio of power emitted per unit area by O_{1 }to that of O_{2} is :**

- (A) 1/81
- (B) 1/9
- (C) 9
- (D) 81

**Q3. The speed of an electron, whose de-Broglie wavelength is equal to its compton wavelength, is (c is the speed of light)**

- (A) c
- (B)
^{c}/_{√2} - (C)
^{c}/_{2} - (D)
^{c}/2

**Q4. If the uncertainty in the location of a particle is equal to its de-Broglie wavelength, then the uncertainty in its velocity V is**

- (A)
^{V}/_{2} - (B) V
- (C)
^{V}/_{4 } - (D)
^{V}/_{3}

**Q5. The photoelectric threshold for tungsten is 2300 Å. The energy of the electrons emitted from the surface incident on the tungsten (h = 6.63 x 10 ^{-34} J-sec) is**

- (A) 2.39 x 10
^{-12}joule - (B) 2.39 x 10
^{-19}joule - (C) 1.48 x 10
^{-19}joule - (D) 3.56 x 10
^{-19}joule

**Q6. An electron has a speed of 300 m/sec accurate up to 0.01%. With what fundamental accuracy can locate the position of this electron (mass of electron, me = 9.1 x 10 ^{-31} kg, charge, e = 1.6 x 10^{-19} coulomb and Planck’s constant h = 6.64 x 10^{-34} joules / sec ) ?**

- (A) 2.4 cm
- (B) 1.2 cm
- (C) 1.8 cm
- (D) 3.6 cm

**Q7. X-rays of 10.0 p.m. are scattered from a target. The maximum energy of the recoil electron (h/mc for electron is 2.426 ×10 ^{-12} m) is**

- (A) 3.27 x 10
^{-15}joules - (B) 6.54 x 10
^{-15}joules - (C) 5.64 x 10
^{-15}joules - (D) 2.37 x 10
^{-15}joules

**Q8. In Compton scattering, wavelength shift is towards**

- (A) shorter wavelength
- (B) longer wavelength
- (C) shorter or longer depending on the angle of scattering
- (D) shorter or longer side depending on photon energy

**Q9. The photon energy for light of wavelength 3.1 x 10 ^{-7} m is [hc = 1.24 x 10^{-6} eVm]**

- (A) 3.1 eV
- (B) 6.2 eV
- (C) 2.4 eV
- (D) 4.0 eV

**Q10. The uncertainty relation holds for the following situation**

- (A) holds for particles only
- (B) does not hold for microscopic particles
- (C) holds for both microscopic and macroscopic particles
- (D) depends on the nature of the particle

**Q11. If the Broglie wavelength of an electron and proton are equal, then**

- (A) the velocity of proton is less than that of the electron
- (B) the velocities of proton and electron are equal
- (C) the velocity of proton is greater than that of the electron
- (D) the energy of electron is less than that of the proton

**Q12. The position and momentum of a 1 keV electron are simultaneously determined. If its position is located to within 1 Å, what is the percentage of uncertainty in its momentum?**

- (A) 0.61
- (B) 6.17
- (C) 61.73
- (D) 0.061

**Q13. The photoelectric equation is derived under the assumption that**

- (A) electrons are associated with waves of wavelength λ =
^{h}/_{p}where P is the momentum - (B) light is emitted only when electrons jump between the orbits
- (C) light is absorbed in quanta of energy E = hν
- (D) light behaves like a wave

**Q14. The number of electrons emitted increases if the incident light has**

- (A) higher frequency
- (B) higher wavelength
- (C) higher intensity
- (D) lower frequency

**Q15. The photoelectric threshold for a metal is 3000 Å. The kinetic energy of an electron ejected from it by radiation of wavelength 1200 Å is**

- (A) 3.1 eV
- (B) 12.6 eV
- (C) 6.2 eV
- (D) 21.4 eV

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*Answer Key* (if you find any answer wrong, feel free to Correct us)

*Answer Key*

01. | (B) | 06. | (A) | 11. | (A) |

02. | (D) | 07. | (B) | 12. | (D) |

03. | (B) | 08. | (B) | 13. | (C) |

04. | (B) | 09. | (D) | 14. | (C) |

05. | (B) | 10. | (C) | 15. | (C) |