Quantum Theory Questions

VIDYANCHAL

The Pioneer Academy for IIT-JEE / PMT Coaching Page N o. ( 1)

1. The equation E= hν was deduced by: (a) Heisenberg (b) de Broglie (c) Einstein (d) Planck 2. Millikan's oil drop experiment is used to find: (a) e/m ratio of electron (b) Electronic charge (c) Mass of an electron (d) Velocity of an electron 3. The e/m for positive rays in comparison to cathode rays is: (a) Very low (b) High (c) Same (d) None 4. Which has highest e/m ratio? (a) He2+ (b) H+ (c) He+ (d) H 5. The ratio of e/m, i. e., specific charge for a cathode ray: (a) Has the smallest value when the discharge tube is filled with H2 (b) Is constant (c) Varies with the atomic number of gas in the discharge tube (d) Varies with the atomic number of an element forming the cathode 6. The velocity of a photon is: (a) Independent of its wavelength (b) Depends on its wavelength (c) Depends on its source (d) Equal to square of its amplitude 7. Which is not characteristics of Planck's quantum theory of radiation? (a) Radiation is associated with energy (b) Energy is not absorbed or emitted in whole number or multiples of quantum (c) The magnitude of energy associated with a quantum is proportional to the frequency (d) Radiation energy is neither emitted nor absorbed continuously but in small packets called quanta 8. Light, a well known form of energy, is treated as a form of matter, by saying that it consists of: (a) Photons or bundles of energy (b) Electrons or a wave like matter (c) Neutrons, since electrically neutral (d) None of the above 9. Which is not electromagnetic radiation? (a) Infrared rays (b) X-rays (c) Cathode rays (d) y-rays 10.Which wave property is directly proportional to energy of electromagnetic radiation: (a) Velocity (b) Frequency (c) Wave number (d) All of these 11. Cathode rays are produced when the pressure in the discharge tube is of the order of: (a) 76 cm of Hg (b) 10-6 cm of Hg (c) 1 cm of Hg (d) 10-2 to 10-3 mm of Hg 12. Positive rays or canal rays are: (a) Electromagnetic waves (b) A steam of positively charged gaseous ions (c) A stream of electrons (d) Neutrons 13. Photoelectric effect is the phenomenon in which: (a) Photons come out of a metal when it is hit by a beam of electrons (b) Photons come out of the nucleus of an atom under the action of an electric field (c) Electrons come out of a metal with a constant velocity which depends on the frequency and intensity of incident light wave (d) Electrons come out of a metal with different velocities not greater than a certain value which depends only on the frequency of the incident light wave and not on its intensity 14. Einstein's theory of photoelectric effect is based on: (a) Newtons corpuscular theory of light (b) Huygen's wave theory of light (c) Maxwell's electromagnetic theory of light (d) Planck's quantum theory of light 15. In photoelectric effect, the photo-current: (a) Increases with increase of frequency of incident photon (b) Decreases with increase of frequency of incident photon ~ (c) Does not depend on the frequency of photon but depends only on the intensity of incident light (d) Depends both on intensity and frequency of the incident photon 16. In photoelectric effect the number of photo- electrons emitted is proportional to: (a) Intensity of incident beam (b) Frequency of incident beam (c) Velocity of incident beam (d) Work function of photo cathode 17. Increase in the frequency of the incident radiations increases the: (a) Rate of emission of photo-electrons (b) Work function (c) Kinetic energy of photo-electrons (d) Threshold frequency 18. Threshold wavelength depends upon: (a) Frequency of incident radiation (b) Velocity of electrons (c) Work function (d) None of the above 19. The study of photoelectric effect is useful in understanding: (a) Conservation of energy (b) Quantization of charge (c) Conservation of charge (d) Conservation of kinetic energy 20. The work-function for photoelectric effect: (a) Depends upon the frequency of incident light (b) Is same for all metals (c) Is different for different metals (d) None of the above 21. Einstein's photoelectric equation states that Ek =hv- W. In this equation, Ek refers to: (a) Kinetic energy of all ejected electrons (b) Mean kinetic energy of emitted electrons

Concept by Devender singh

india 9897888342

VIDYANCHAL

The Pioneer Academy for IIT-JEE / PMT Coaching Page N o. ( 2)

(c) Minimum kinetic energy of emitted electrons (d) Maximum kinetic energy of emitted electrons 22. A photon is: (a) A quanta of light (or electromagnetic) energy (b) A quanta of matter (c) A positively charged particle (d) An instrument for measuring light intensity 23. Photoelectric effect can be caused by: (a) Visible light but not by X-rays (b) Gamma-rays but not by X-rays (c) Ultraviolet light only (d) Visible light, ultraviolet rays, X-rays and gamma rays also 24. If E1, E2 and E3 represent respectively the kinetic energies of an electron, an alpha particle and a proton each having same de Broglie wavelength then: (a) E1 >E3>E2 (b) E2 >E3>E1 (c) £, > E2 > E3 (d) E1 = E2 = E3 25. The best metal to be used for photoemission is: (a) Potassium (b) Sodium (c) Ceasium (d) Lithium 26. A quanta will have more energy if: (a) The wavelength is larger (b) The frequency is higher (c) The amplitude is higher (d) The velocity is lower 27. The minimum energy required to eject an electron from an atom is called: (a) Kinetic energy (b) Electrical energy (c) Chemical energy (d) Work function 28. When light is directed at the metal surface, the emitted electrons: (a) Are called photons (b) Have random energies(c) Have energies that depend upon intensity of light (d) Have energies that depend upon the frequency of light 29. The photoelectric effect occurs only when the incident light has more frequency than a certain minimum: (a) Frequency (b) Wavelength (c) Speed (d) Charge 30. The Planck's constant has a unit of: (a) Work (b) Energy (c) Angular momentum (d) Linear momentum 31. In photoelectric emission the energy of the emitted electrons is: (a) Larger than that of incident photon (b) Smaller than that of incident photon (c) Same as that of incident photon (d) Proportional to intensity of incident light 32. When the frequency of light incident on a metallic plate is doubled, the KE of the emitted photoelectrons will be: (a) Doubled (b) Halved (c) Increased but more than doubled of the previous KE (d) Unchanged 33. The energy of electromagnetic radiation depends on: (a) Amplitude and wavelength (b) Wavelength (c) Amplitude (d) Temperature of medium through which it passes 34. The ratio of the energy of a photon of 2000 Å wavelength radiation to that of 4000 Å radiation is: (a) 1/4 (b) 1/2 (c) 2 (d) 4 35. The frequency of a green light is 6 x 1014 Hz. Its wavelength is: (a) 500 nm (b) 5 nm (c)50,000nm (d) None of these 36. The maximum wavelength of light that can excite an electron from first to third orbit of hydrogen atom is: (a) 487 nm (b) 170 nm (c) 103 nm (d) 17 nm 37. The ratio of specific charge e/m of a proton to that of an α-particle is: (a) 1 : 4 (b) 1 : 2 (c) 1 : 1/4 (d) 1 : 1/2 38. The specific charge of a proton is 9.6 x 107 C kg-1, then for an α-particles it will be: (a) 2.4 x 107 Ckg-1 (b) 4.8x 107 Ckg-1 (c) 19.2 x 107 Ckg-1 (d) 38.4 x 107 C Kg-1 39. The rest mass of a photon of wavelength  is: (a) Zero (b) hc/  (c) h/c  (d) h/  40. The work function for a metal is 4 eV. To emit a photo electron of zero velocity from the surface of the metal, the wavelength of incident light should be: (a) 2700 Å (b) 1700 Å (c) 5900 Å (d) 3100 Å 41. Ultraviolet light of 6.2 eV falls on aluminium surface (work function = 4.2 eV). The kinetic energy (in joule) of the fastest electron emitted is approximately: (a) 3 x 10-21 (b) 3 x 10-19 (c) 3 x 10-17 (d) 3 x 10-15 42. The threshold wavelength for photoelectric effect on sodium is 5000 Å. Its work function is: (a) 4 x 10-19 J (b) 1 J (c) 2 x 10-19 J (d) 3 x 10-10 J 43. Photons of energy 6 eV are incidented on a potassium surface of work function 2.1 eV. What is the stopping potential?(a) -6V (b) -2.1V (c) -3.9V (d) -8.1V 44. Suppose 10-17 J of light energy is needed by the interior of human eye to see an object. The photons of green light (  = 550 nm) needed to see the object are: (a) 27 (b) 28 (c) 29 (d) 30 45. A photon of 300 nm is absorbed by a gas and then reemits two photons. One reemitted photon has wavelength 496 nm, the wavelength of second reemitted photon is:(a) 757 (b) 857 (c) 957 (d) 657 46. An atom emits energy equal to 4x 10-12 erg. To which part of electromagnetic spectrum it belongs: (a) UV region (b) Visible region (c) IR region (d) Microwave region 47. The energy ∆E corresponding to intense yellow line of sodium of  =589 nm is: (a) 2.10 eV (b) 43. 37 eV (c) 47.12 eV (d) 2.11 kcal 48. The momentum of a photon of frequency 5 x 1017 s -1 is nearly: (a) 1.1 x 10-24 kg ms-1 (b) 3.33 x 10-43 kg ms-1 (c) 2.27 x 10-40 kg ms-1 (d) 2.27 x 10-38 kg ms-1

Concept by Devender singh

india 9897888342

VIDYANCHAL

The Pioneer Academy for IIT-JEE / PMT Coaching Page N o. ( 3)

49. When a gold sheet is bombarded by a beam of α-particles, only a few of them get deflected whereas most go straight, undeflected. This is because (a) the force of attraction exerted on the α-particles by the oppositely charged electrons is not sufficient (b) a nucleus has a much smaller volume than that of an atom (c) the force of repulsion acting on the fast-moving a-particles is very small (d) the neutrons in the nucleus do not have any effect on the α-particles 50. In which of the following is the radius of the first orbit minimum? (a) A hydrogen atom (b) A tritium atom (c) Triply ionized beryllium (d) Doubly ionized helium 51. From the α-particle scattering experiment, Rutherford concluded that (a) α-particles can come within a distance of the order of 10-14 m of the nucleus (b) the radius of the nucleus is less than 10-14 m(c) scattering follows Coulomb's law (d) the positively charged parts of the atom move with extremely high velocities 52. Rutherford's scattering formula fails for very small scattering angles because (a) the full nuclear charge of the target atom is partially screened by its electron (b) the impact parameter between the α-particle source and the nucleus of the target is very large compared to the size of the nucleus (c) the kinetic energy of the α-particles is large (d) the gold foil is very thin 53. Choose the correct statements. (a) Every object emits radiation whose predominant frequency depends on its temperature. (b) The quantum energy of a wave is proportional to its frequency. (c) Photons are quanta of light. (d) The value of the Planck constant depends on energy. 54. Calculate the number of protons, neutrons and electrons in 8035Br. 55. Find out the atomic number, mass number, number of protons, electrons and neutrons present in the element with the notation 23892U. 56. The number of electrons, protons and neutrons in a species are equal to 18, 16 and 16 respectively. Assign the proper symbol to the species. 57. Neutrons can be found in all atomic nuclei except in one case. Which is this atomic nucleus and what does it consist of? 58. How many nucleons are present in an atom of Nobelium, 254102No? How many electrons are present in the atom? How many nucleons may be considered as neutrons? 59. Complete the following table:

60. Calculate (a) wave number and (b) frequency of yellow radiations having Wavelength of 5800 Å. 61. Calculate the frequency of infrared radiations having wavelength, 3 x 106 nm. 62. Calculate the range of frequencies of visible light from 3800–7600 Å. 63. How long would it take a radiowave of frequency, 6 x 103 sec-1 to travel from Mars to the Earth, a distance of 8 x 107 km? 64. Calculate the wave number of radiations having a frequency of 4 x 1014 Hz. 65. The Vividh Bharati station of All India Radio, Delhi broadcasts at a frequency of 1368 kHz (kilohertz). Calculate the wavelength of the electromagnetic radiation emitted by the transmitter. Which part of the electromagnetic spectrum does it belong to? 66. The wavelength range of the visible spectrum extends from violet (400 nm) to red (750 nm). Express these wavelengths in frequencies (Hz) (1 nm = 10-9 m) 67. Calculate (a) wave number (b) frequency of yellow radiation having wavelength of 5800 Å. 68. Calculate the kinetic energy of the electron ejected when yellow light of frequency 5.2 x 1014 sec-1 falls on the surface of potassium metal. Threshold frequency of potassium is 5 x 1014 sec-1. 69. Calculate the energy of a mole of photons of radiations whose frequency is 5 x 1014 Hz? 70. Which has a higher energy: a photon of red light with a wavelength of 7500 Å or a photon of green light with a wavelength of 5250 Å? 71. In the ultraviolet region of the atomic spectrum of hydrogen, a line is obtained at 1026 Å Calculate the energy of photon of this wavelength (h = 6.626 x 10-34 J-sec). 72. In the infrared region of the atomic spectrum of hydrogen, a line is obtained at 3802 cm-1. Calculate the energy of this photon (h = 6.626 X 10-34 J sec).

Concept by Devender singh

india 9897888342

VIDYANCHAL

The Pioneer Academy for IIT-JEE / PMT Coaching Page N o. ( 4)

73. Light of wavelength 4000 Å falls on the surface of cesium. Calculate the energy of the photo-electron emitted. The critical wavelength for photoelectric effect in cesium is 6600 Å 74. What is the ratio between the energies of two radiations, one with a wavelength of 6000 Å and the other with 2000 Å [1Å=10-10 m]? 75. The threshold energy for photo-electric emission of electrons from a metal is 3.056 x 18-15 joule. If light of 4000 Å wave, length is used, will the electrons be ejected or not? (h = 6.63 x 10-34. Joule sec). 76. Calculate the wavelength of a photon in Angstrom units having energy of one electron volt. 77. Why cathode rays are produced only when the pressure of the w\$ inside the discharge tube is very low? 78. Give two s from everyday life where cathode ray tubes are used. 79. What is the difference in the origin of cathode rays and anode rays? 80. In one discharge tube, H2 gas is taken and in the other O2 gas is taken. Will the electrons and positive ions in the cathode rays and in the anode rays be same or different? 81. When α-rays hit a thin foil of gold, very few α-particles are deflected back. What does it prove? 82. What is the difference between atomic mass and mass number? 83. Give one of each of the following:(i) Isotope of 3517Cl(ii) Isobar of 4018Ar (iii) Isotone of 146C 84. What is the main difference between electromagnetic wave theory and Planck's quantum theory? 85. What is the difference between a quantum and a photon? 86. How are frequency and wave number related to each other? 87. Arrange X-rays, cosmic rays and radiowaves according to frequency. Answers:1. (b)2.(b)3. (a)4.(b)5. (b)6.(a)7.(b)8.(a)9.(c)10.(d)11.(d) 12.b)13.(d)14.(d)15.(c)16.(a)17.(c)18.(c) 19. (b)20.(c)21.(d) 22.(a)23.(d)24.(a) 25.(c)26.(b)27.(d)28.(d)29.(a)30.(c)31.b)32.(c)33.(b)34.(c) 35.(a)36.c)37.d)38. (b)39.(a)40.(d)41.(b)42.(a) 43.(c)44.b)45.(a)46.(b)47.(a) 48.(a)49.(b)50.(c) 51.(a)(b)(c)52.(a)(b)53.(a)(b)(c)54.35 ,45,35 55.92 ,238 ,92 ,92 ,146 56.Electrons = 18, Protons = 16, Neutrons = 16 57.The nucleus of hydrogen atom does not contain any neutrons. It consists of only one proton. 58. Nucleons = 254, electrons = 102 and neutrons = 254—102 = 152

59. 60. (a) Calculation of the wave 11 -1 number 61. 10 s 62.[ 3.95 x 1014 to 7.89 x 1014 s-1] 63. 64.[ 1.33 4 -1 44 x 10 cm ] 65. [ 219.3 m, Radiowave]66. [ 4.0 x 10 to 7.5 x 1014 Hz) 67. [ (a) 1.724 x 104 cm-1 (b) 5.172 x 1014 s-1] 68. K.E. of the ejected electron is given by 1.325x 10-20 joules 69. [ 199.51 kJ mol-1] 70. [ Green] 71. [1.937 x 10-18 J] 72. [ 7.56 x 10-20J] 73. [ 195 x 10-19 joule] 74. 1/3 75. [ No] 76. 12.40 x 103 Å 77. At higher pressure (e.g., at 1 atmospheric pressure), no electric current flows through the tube because gases are poor conductor of electricity. 78. (i) Television picture tube (ii) fluorescent light tubes. 79. Cathode rays originate from the cathode whereas anode rays are not produced from the anode. They are produced from the gaseous atoms by knock out of the electrons by high speed cathode rays. 80. Electrons will be same but positive ions will not be same. 81. There is a very small heavy body present within the atom, called nucleus. 82. Mass number is a whole number because it is the sum of number of protons and numbers of neutrons whereas atomic mass is fractional because it is the average relative mass of its atoms as compared with mass an atom of C – 12 isotope taken as 12. 83. 84. According to electromagnetic wave theory, the energy is emitted or absorbed continuously whereas according to Planck's quantum theory, energy is emitted or absorbed discontinuously, i.e., in certain definite packets called 'quanta'. 85. The smallest packet of energy of any radiation is called a quantum whereas that of light is called photon. 86. where c is velocity of light, v is frequency and v is wave number. 87. Cosmic rays > X-rays > Radio waves

Concept by Devender singh

india 9897888342

VIDYANCHAL

The Pioneer Academy for IIT-JEE / PMT Coaching Page N o. ( 5)

Concept by Devender singh

india 9897888342