Title 24. Atomic Physics -1 Easy.pdf ✅

1. In the Millikan's experiment, the distance between two horizontal plates is 2.5 cm and the potential difference applied is 250 V. The electric field between the plates will be (a) 900 V/m (b) 10000 V/m (c) 625 V/m (d) 6250 V/m 2. The cathode rays have particle nature because of the fact that (a) They can propagate in vacuum (b) They are deflected by electric and magnetic fields (c) They produced fluorescence (d) They cast shadows 3. In Millikan's experiment for the determination of the charge on the electron, the reason for using the oil is (a) It is a lubricant (b) Its density is higher (c) It vapourises easily (d) It does not vapourise 4. The mass of a particle is 400 times than that of an electron and the charge is double. The particle is accelerated by 5 V. Initially the particle remained in rest, then its final kinetic energy will be (a) 5 eV (b) 10 eV (c) 100 eV (d) 2000 eV 5. An electron (charge = C 19 1.6 10 −  ) is accelerated through a potential of 100,000 V. The energy acquired by the electron is (a) J 24 1.6 10 −  (b) erg 14 1.6 10 −  (c) J 17 0.53 10 −  (d) J 14 1.6 10 −  6. While doing his experiment, Millikan one day observed the following charges on a single drop (i) C 19 6.563 10 −  (ii) C 19 8.204 10 −  (iii) C 19 11 .50 10 −  (iv) C 19 13 .13 10 −  (v) C 19 16 .48 10 −  (vi) C 19 18 .09 10 −  From this data the value of the elementary charge (e) was found to be (a) C 19 1.641 10 −  (b) C 19 1.630 10 −  (c) C 19 1.648 10 −  (d) C 19 1.602 10 −  7. When electron beam passes through an electric field, they gain kinetic energy. If the same beam passes through magnetic field, then (a) Their energy increases (b) Their momentum increases (c) Their potential energy increases (d) Energy and momentum both remains unchanged 8. Which of the following law is used in the Millikan's method for the determination of charge (a) Ampere's law (b) Stoke's law (c) Fleming's left hand rule (d) Fleming's right hand rule 9. The mass of the electron varies with (a) The size of the cathode ray tube (b) The variation of ‘g’ (c) Velocity (d) Size of the electron 10. When the speed of electrons increases, then the value of its specific charge (a) Increases (b) Decreases (c) Remains unchanged (d) Increases upto some velocity and then begins to decrease 11. An electron is accelerated through a potential difference of 1000 volts. Its velocity is nearly (a) 3.8 10 m /s 7  (b) 1.9 10 m /s 6  (c) 1.9 10 m /s 7  (d) 5.7 10 m /s 7  12. In an electron gun the control grid is given a negative potential relative to cathode in order to (a) Decelerate electrons (b) Repel electrons and thus to control the number of electrons passing through it (c) To select electrons of same velocity and to converge them along the axis (d) To decrease the kinetic energy of electrons 13. The ratio of momenta of an electron and an  − particle which are accelerated from rest by a potential difference of 100 V is (a) 1 (b) m 2me (c) m me (d) m me 2 14. When subjected to a transverse electric field, cathode rays move (a) Down the potential gradient (b) Up the potential gradient (c) Along a hyperbolic path (d) Along a circular path 15. The fact that electric charges are integral multiples of the fundamental electronic charge was proved experimentally by
(a) Planck (b) J.J. Thomson (c) Einstein (d) Millikan 16. In Millikan oil drop experiment, a charged drop of mass kg 14 1.8 10 −  is stationary between its plates. The distance between its plates is 0.90 cm and potential difference is 2.0 kilo volts. The number of electrons on the drop is (a) 500 (b) 50 (c) 5 (d) 0 17. The charge on electron was discovered by (a) J.J. Thomson (b) Neil Bohr (c) Millikan (d) Chadwick 18. From the following, what charges can be present on oil drops in Millikan's experiment (a) Zero, equal to the magnitude of charge on  − particle (b) 2 , 1.6 10 , 18 e C −  (c) 1.6 10 C, 2.5e −19  (d) 1.5e, e (Here e is the electronic charge) 19. A narrow electron beam passes undeviated through an electric field E 3 10 volt/m 4 =  and an overlapping magnetic field 3 2 B 2 10 Weber /m − =  . If electric field and magnetic field are mutually perpendicular. The speed of the electrons is (a) 60 m/s (b) 10.3 10 m /s 7  (c) 1.5 10 m /s 7  (d) 0.67 10 m /s −7  20. In Thomson's method of determining e/m of electrons (a) Electric and magnetic fields are parallel to electrons beam (b) Electric and magnetic fields are perpendicular to each other and perpendicular to electrons beam (c) Magnetic field is parallel to the electrons beam (d) Electric field is parallel to the electrons beam 21. Cathode rays enter into a uniform magnetic field perpendicular to the direction of the field. In the magnetic field their path will be (a) Straight line (b) Circle (c) Parabolic (d) Ellipse 22. The specific charge of an electron is (a) coulomb 19 1.6 10 −  (b) stat coulomb 10 4.8 10 −  (c) 1.76 10 coulomb / kg 11  (d) 1.76 10 coulomb / k g −11  23. An electron is moving with constant velocity along x − axis. If a uniform electric field is applied along y − axis, then its path in the x −y plane will be (a) A straight line (b) A circle (c) A parabola (d) An ellipse 24. Cathode rays are similar to visible light rays in that (a) They both can be deflected by electric and magnetic fields (b) They both have a definite magnitude of wavelength (c) They both can ionise a gas through which they pass (d) They both can expose a photographic plate 25. Which one of the following devices makes use of the electrons to strike certain substances to produce fluorescence (a) Thermionic valve (b) Photoelectric cell (c) Cathode ray oscilloscope (d) Electron gun 26. An oxide coated filament is useful in vacuum tubes because essentially (a) It has high melting point (b) It can withstand high temperatures (c) It has good machanical strength (d) It can emit electrons at relatively lower temperatures 27. Gases begin to conduct electricity at low pressure because (a) At low pressure, gases turn to plasma (b) Colliding electrons can acquire higher kinetic energy due to increased mean free path leading to ionisation of atoms (c) Atoms break up into electrons and protons (d) The electrons in atoms can move freely at low pressure 28. A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength 1 20 − Vm and 0.5 T at right angles to the direction of motion of the electrons. What is the velocity of the electrons (a) 20 −1 ms (b) 40 −1 ms (c) 8 −1 ms (d) 5.5 −1 ms 29. Kinetic energy of emitted cathode rays is dependent on (a) Only voltage (b) Only work function (c) Both (a) and (b) (d) It does not depend upon any physical quantity 30. The radius of the orbital of electron in the hydrogen atom 0.5 Å. The speed of the electron is 2 10 m /s 6  . Then the current in the loop due to the motion of the electron is
(a) 1 mA (b) 1.5 mA (c) 2.5 mA (d) mA 2 1.5 10 −  31. The kinetic energy of an electron which is accelerated through a potential of 100 volts is (a) J 17 1.602 10 −  (b) 418.6 calories (c) K 4 1.16 10 (d) 34 6.626 10 −  W- sec 32. When a proton is accelerated with 1 volt potential difference, then its kinetic energy is (a) eV 1840 1 (b) 1840 eV (c) 1 eV (d) 1840 c 2 eV 33. Energy of electrons can be increased by allowing them (a) To fall through electric potential (b) To move in high magnetic field (c) To fall from great heights (d) To pass through lead blocks 34. Cathode rays and canal rays produced in a certain discharge tube are deflected in the same direction if (a) A magnetic field is applied normally (b) An electric field is applied normally (c) An electric field is applied tangentially (d) A magnetic field is applied tangentially 35. In a Millikan's oil drop experiment the charge on an oil drop is calculated to be C 19 6.35 10 −  . The number of excess electrons on the drop is (a) 3.9 (b) 4 (c) 4.2 (d) 6 36. Cathode rays consist of (a) Photons (b) Electrons (c) Protons (d)  -particles 37. A metal plate gets heated, when cathode rays strike against, it due to (a) Kinetic energy of cathode rays (b) Potential energy of cathode rays (c) Linear velocity of cathode rays (d) Angular velocity of cathode rays 38. Cathode rays are (a) Positive rays (b) Neutral rays (c) He rays (d) Electron waves 39. An electron of charge ‘e’ coulomb passes through a potential difference of V volts. Its energy in ‘joules’ will be (a) V / e (b) eV (c) e /V (d) V 40. An electron is accelerated through a potential difference of 200 volts. If e /m for the electron be 11 1.6  10 coulomb/kg, the velocity acquired by the electron will be (a) 8 10 m /s 6  (b) 8 10 m /s 5  (c) 5.9 10 m /s 6  (d) 5.9 10 m /s 5  41. Which is not true with respect to the cathode rays (a) A stream of electrons (b) Charged particles (c) Move with speed same as that of light (d) Can be deflected by magnetic fields 42. In Milikan’s experiment, an oil drop having charge q gets stationary on applying a potential difference V in between two plates separated by a distance ‘d’. The weight of the drop is (a) qVd (b) V d q (c) Vd q (d) d V q 43. Electron volt is a unit of (a) Potential (b) Charge (c) Power (d) Energy 44. In Thomson experiment of finding e /m for electrons, beam of electron is replaced by that of muons (particle with same charge as of electrons but mass 208 times that of electrons). No deflection condition in this case satisfied if (a) B is increased 208 times (b) E is increased 208 times (c) B is increased 14.4 times (d) None of these 45. The colour of the positive column in a gas discharge tube depends on (a) The type of glass used to construct the tube (b) The gas in the tube (c) The applied voltage (d) The material of the cathode 46. Cathode rays are produced when the pressure is of the order of (a) 2 cm of Hg (b) 0.1 cm of Hg (c) 0.01 mm of Hg (d) 1 m of Hg 47. The speed of an electron having a wavelength of m 10 10 − is (a) 7.25 10 m /s 6  (b) 6.26 10 m / s 6  (c) 5.25 10 m /s 6  (d) 4.24 10 m /s 6 
48. Which of the following is not the property of a cathode ray (a) It casts shadow (b) It produces heating effect (c) It produces flurosence (d) It does not deflect in electric field 49. In a Thomson set-up for the determination of e/m, electrons accelerated by 2.5 kV enter the region of crossed electric and magnetic fields of strengths 4 1 3.6 10 −  Vm and T 3 1.2 10 −  respectively and go through undeflected. The measured value of e /m of the electron is equal to (a) 11 1 1.0 10 - −  C kg (b) 11 1 1.76 10 - −  C kg (c) 11 1 1.80 10 - −  C kg (d) 11 1 1.85 10 - −  C kg 50. The ratio of specific charge of an  -particle to that of a proton is (a) 2 : 1 (b) 1 : 1 (c) 1 : 2 (d) 1 : 3 51. In Bainbridge mass spectrograph a potential difference of 1000 V is applied between two plates distant 1 cm apart and magnetic field in B = 1T. The velocity of undeflected positive ions in m/s from the velocity selector is (a) 10 m /s 7 (b) 10 m /s 4 (c) 10 m /s 5 (d) 10 m /s 2 52. When cathode rays (tube voltage ~ 10 kV) collide with the anode of high atomic weight then we get (a) Positive rays (b) X-rays (c) Gamma rays (d) Canal rays 53. In Thomson's experiment if the value of q/m is the same for all positive ions striking the photographic plate, then the trace would be (a) Straight line (b) Parabolic (c) Circular (d) Elliptical 54. In a discharge tube at 0.02 mm, there is a formation of (a) FDS (b) CDS (c) Both space (d) None of these 55. Electric field and magnetic field in Thomson mass spectrograph are applied (a) Simultaneously, perpendicular (b) Perpendicular but not simultaneously (c) Parallel but not simultaneously (d) Parallel simultaneously 56. The current conduction in a discharged tube is due to (a)Electrons only (b) +ve ions and electrons (c) – ve ions and electrons (d) + ve ions, – ve ions and electrons 57. In Milikan's oil drop experiment, a charged drop falls with terminal velocity V. If an electric field E is applied in vertically upward direction then it starts moving in upward direction with terminal velocity 2V. If magnitude of electric field is decreased to 2 E , then terminal velocity will become (a) 2 V (b) V (c) 2 3V (d) 2V 58. An electron is accelerated through a p.d. of 45.5 volt. The velocity acquired by it is (in ms-1 ) (a) 6 4 10 (b) 4 4 10 (c) 6 10 (d) Zero 59. A cathode emits 14 1.8 10 electrons per second, when heated. When 400V is applied to anode all the emitted electrons reach the anode. The charge on electron is C 19 1.6 10 −  . The maximum anode current is (a) 2.7A (b) 29 A (c) 72A (d) 29 mA 60. Order of q/m ratio of proton,  -particle and electron is (a) e  p  (b) p   e (c) e   p (d) None of these 61. A charge of magnitude 3e and mass 2m is moving in an electric field E. The acceleration imparted to the charge is (a) 2Ee / 3m (b) 3Ee / 2m (c) 2m / 3Ee (d) 3m / 2Ee 62. An electron initially at rest, is accelerated through a potential difference of 200 volt, so that it acquires a velocity 8.4 10 / . 6  m s The value of e/m of electron will be (a) 2.76 10 C / kg 12  (b) 1.76 10 C / kg 11  (c) 0.76 10 C / kg 12  (d) None of these 63. An  particle is accelerated through a p.d of 6 10 volt then K.E. of particle will be (a) 8 MeV (b) 4 MeV (c) 2 MeV (d) 1 MeV 64. Positive rays consists of (a) Electrons (b) Neutrons (c) Positive ions (d) Electro magnetic waves