3. Modern Physics-PART TEST - 1

PART TEST - 1 (PT-1) TOPIC : MODERN PHYSICS (PHYSICS) Duration : 1 Hour Max. Marks : 90 GENERAL INSTRUCTIONS 1. This Question Paper contains 30 objective type questions. 2. Each question has 4 choices (A), (B), (C) and (D), out of which only one is correct. 3. For each question, you will be awarded 3 Marks if you give the correct answer and zero Mark if no answer is given. In all other cases, minus one (–1) Mark will be awarded. SECTION - I Straight Objective Type This section contains 30 Single choice questions. Each question has choices (A), (B), (C) and (D), out of which ONLY ONE is correct. 1. A radioactive nuclide A decays to nuclide B which further decays to C. Their disintegration constant are 1 and 2 respectively. At t = 0 only nuclei A are present. Number of nuclei A at t = 0 is N0. A 1 B 2  C t = 0 N0 0 0 t N1 N2 N3 In the above radioactive decay C is stable nucleus. Then: (A) rate of decay of A will first increase and then decrease (B) number of nuclei of B will first increase and then decrease (C) if 2 > 1, then activity of B will always be higher than activity of A (D) if 1 >> 2, then number of nucleus of C will always be less than number of nucleus of B. 2. An enclosure filled with helium is heated to a temperature of 400 K. Helium atom emerges out of the enclosure. The mean debroglie wavelength of the helium atoms is : (A) 0.44 Å (B) 0.63 Å (C) 0.77 Å (D) none of these 3. When a metallic surface is illuminated with monochromatic light of wavelength , the stopping potential is 5 V . When the same surface is illuminated with light of wavelength 3, the stopping potential is V . 0 0 Then the work function of the metallic surface is : hc (A) 6  hc (B) 5  hc (C) 4  (D) (D) 2 hc 4  4. No. of identical photons incident on a perfectly black body of mass m kept at rest on smooth horizontal surface. Then the acceleration of the body if n number of photons incident per second is (Assume wavelength of photon to be ) : (A) nh 2m nh (B) m (C) 2nh m m (D) nh 10. Both the frequency and the intensity of a beam of light falling on the surface of photoelectric material are increased by a factor of two. This will : (A) increase both, the maximum kinetic energy of the photo-electrons, as well as photoelectric saturation current by a factor of two. (B) increase the maximum kinetic energy of the photo-electrons by a factor greater than two and would increase the photoelectric saturation current by a factor of two. (C) increase the maximum kinetic energy of the photoelectrons by a factor greater than two and will have no effect on the magnitude of the photoelectric saturation current produced. (D) increase the maximum kinetic energy of the emitted photo-electrons by a factor of two but will have no effect on the saturation photoelectric current. 11. The photon radiated from hydrogen corresponding to 2nd line of Lyman series is absorbed by a hydrogen like atom ‘X’ in 2nd excited state. As a result the hydrogen like atom ‘X’ makes a transition to nth orbit. Then, (A) X = He+, n = 4 (B) X = Li++, n = 6 (C) X = B+++, n = 6 (D) X = Li++, n = 9 12. The angular momentum of an electron in first orbit of Li++ ion is : 3 h (A) 2  9 h (B) 2  h (C) 2  h (D) 6  13. An electron of mass ' m ', when accelerated through a potential V has deBroglie wavelength . The de Broglie wavelength associated with a proton of mass M accelerated through the same potential difference will be: (A)  (B)   M (C)   m (D)   m M 14. Two hydrogen atoms are in excited state with electrons residing in n = 2. First one is moving towards left and emits a photon of energy E1 towards right. Second one is moving towards left with same speed and emits a photon of energy E2 towards left. Taking recoil of nucleus into account during emission process (A) E1 > E2 (B) E1 < E2 (C) E1 = E2 (D) information insufficient 15. In a hydrogen atom following the Bohr’s postulates the product of linear momentum and angular momentum is proportional to (n)x where ‘n’ is the orbit number. Then ‘x’ is : (A) 0 (B) 2 (C) –2 (D) 1 16. One of the lines in the emission spectrum of Li2+ has the same wavelength as that of the 2nd line of Balmer series in hydrogen spectrum. The electronic transition corresponding to this line is : (A) n = 4  n = 2 (B) n = 8  n = 2 (C) n = 8  n = 4 (D) n = 12  n = 6 17. The ratio of wave length of a photon of energy E and deBroglie wavelength of an electron of mass 'm' having the kinetic energy also E is : (Speed of light = c) (A) (B) (C) 2mc 2 E (D) mc2 E 18. An orbital electron in the ground state of hydrogen has an angular momentum L1 and an orbital electron in the first orbit in the ground state of lithium (double ionised positively charged) has an angular momentum L2 .Then : (A) L1 = L2 (B) L1 = 3L2 (C) L2 = 3L1 (D) L2 = 9L1 A nswers 1. (B) 2. (B) 3. (A) 4. (A) 5. (B) 6. (C) 7. (B) 8. (B) 9. (A) 10. (C) 11. (D) 12. (C) 13. (B) 14. (B) 15. (A) 16. (D) 17. (A) 18. (A) 19. (A) 20. (C) 21. (D) 22. (C) 23. (B) 24. (A) 25. (B) 26. (D) 27. (A) 28. (D) 29. (C) 30. (B) 4. If first excitation potential of a hydrogen like atom is V volt, then the ionization energy of this atom will be : (A) V electron volt (B) 3 V electron volt 4 4 V (C) 3 electron volt (D) cannot be calculated by given information. 5. The element which has a k x-rays line of wavelength 1.8 Å is (R = 1.1 × 107 m–1, b = 1 and = 0.39) (A) Co, Z = 27 (B) Fe, Z = 26 (C) Mn, z = 25 (D) Ni, z = 28 6. The radii of nuclei of two atoms are in ratio 3 . Assuming them to be Hydrogen like atom, the ratio of 2 their orbital radius for K shell will be (assume no. of proton = No. of neutron for each atom) 27 (A) 8 (B) 8 27 4 (C) 9 (D) None 7. A radioactive nucleus can decay by either emitting an  particle or by emitting a  particle. Probability of  decay is 75% while that of  decay is 25%. The decayconstant of  decay is  and that of  1 decay is  .  2 is 1 (A) 3 (B) 3 (C) 1 (D) cannot be said 8. A radioactive nucleus ' X' decays to a stable nucleus ' Y '. Then the graph of rate of formation of ' Y' against time ' t ' will be : (A) (B) (C) (D) SECTION - II Multiple Correct Answers Type This section contains 4 Multiple choice questions. Each question has 4 choices (A), (B), (C) and (D), out of which ONE OR MORE may be correct. 15. Statement-1 : When cathode rays (accelerated with high voltage 10 kVolts) strikes a hard metallic surface, highly penetrating radiation is obtained. Statement-2 : Due to conversion of electron's kinetic energy into photon's energy, the shortest wavelength limit of X-rays produced is inversely proportional to the accelerating voltage. (A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1 (B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (C) Statement-1 is True, Statement-2 is False (D) Statement-1 is False, Statement-2 is True. 16. Statement-1 : Heavy nuclides tend to have more number of neutrons than protons. Statement-2 : In heavy nuclei, as there is coloumbic repulsion between protons, so excess of neutrons are preferable. (A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1 (B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (C) Statement-1 is True, Statement-2 is False (D) Statement-1 is False, Statement-2 is True. SECTION - IV Comprehension Type This section contains 2 Paragraphs. Based upon each paragraph, 3 Multiple choice questions have to be answered. Each question has 4 choices (A), (B), (C) and (D), out of which ONLY ONE is correct. Paragraph for Question Nos. 17to 19 An experimental setup of verification of photoelectric effect is shown in the diagram. The voltage across the electrodes is measured with the help of an ideal voltmeter and which can be varied by moving jockey ‘J’ on the potentiometer wire. The battery used in potentiometer circuit is of 20 V and its internal resistance is 2. The resistance of 100 cm long potentiometer wire is 8. The photocurrent is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm2 at separation 0.5 mm are used in the vacuum tube. Photo current in the circuit is very small so we can treat potentiometer circuit an independent circuit. The wavelengths of various colours is as follows : 23. Using Bohr’s model for H–like atom, match the following. Here n = orbit number, Z = nuclear charge, m = mass of electron Column-I Column-II (A) Due to revolving electron, the magnetic field produced (p) n–5 at its centre is proportional to (B) Magnetic moment of revolving electron is proportional to (q) n (C) De-Broglie wave length of revolving electron is proportional to (r) Z3 (D) Areal velocity of revolving electron about nucleus is (s) independent of Z proportional to (t) m–1 24. Match the statements given in column-I with their corresponding possible results in column-II. Column-I Column-II elements is  81  Number of elements having PART TEST - 3 (PT-3) TOPIC : MODERN PHYSICS Duration : 1 Hour Max. Marks : 90 GENERAL INSTRUCTIONS 1. This Question Paper contains 22 questions. 2. For each question in Section I, you will be awarded 3 Marks if you give the correct answer and zero Mark if no answer is given. In all other cases, minus one (–1) Mark will be awarded. 3. For each question in Section II, you will be awarded 4 Marks if you give the correct answer. There is no negative marking. 4. For each question in Section III, you will be awarded 3 Marks if you give the correct answer and zero Mark if no answer is given. In all other cases, minus one (–1) Mark will be awarded. 5. For each question in Section IV, you will be awarded 4 Marks if you give the correct answer and zero Mark if no answer is given. In all other cases, minus one (–1) Mark will be awarded. 6. For each question in Section V, you will be awarded 6 Marks if you give ALL the correct answer(s) or awarded : (i) 1 Mark for correct answer in one row. (ii) 2 Marks for correct answer in two rows. (iii) 4 Marks for correct answer in three rows. 7. For each question in Section VI, you will be awarded 6 Marks if you give the correct answer. There is no negative marking. SECTION - I Straight Objective Type This section contains 8 Single choice questions. Each question has choices (A), (B), (C) and (D), out of which ONLY ONE is correct. 4 1. The wavelengths of K x-rays of two metals ‘A’ and ‘B’ are 1875 R 1 and 675 R respectively, where ‘R’ is Rydberg constant. The number of elements lying between ‘A’ and ‘B’ according to their atomic numbers is (A) 3 (B) 6 (C) 5 (D) 4 2. A free neutron decays to a proton but a free proton does not decay to a neutron out side nucleus. This is beacuse (A) neutron is a composite particle made of a proton and an electron where as proton is fundamental particle (B) neutron is an uncharged particle whereas proton is a charged particle (C) neutron has larger rest mass than the proton (D) weak forces can operate in a neutron but not in a proton. 10. Ionization energy of a hydrogen-like ion B is less than that of hydrogen like ion A. Let r, u, E and L represent the radius of the orbit, speed of the electron, energy of the atom and orbital angular momentum of the electron respectively. In ground state (A) rA > rB (B) uA > uB (C) EA > EB (D) LA > LB 11. Mark the correct options. (A) An atom with a vacancy has smaller energy than a neutral atom (B) K X-ray is emitted when a hole makes a jump from the K shell to some other shell (C) The wavelength of K X-ray is smaller than the wavelength of L X-ray of the same material (D) The wavelength of K X-ray is smaller than the wavelength of K X-ray of the same material 12. An electron makes a transition from n = 2 to n = 1 state in a hydrogen like atom. (A) magnetic field at the site of nucleus is decreased by 16 times. (B) magnetic field at the site of nucleus is increased by 32 times (C) angular momentum of electron is decreased (D) angular momentum of electron is increased SECTION - III Reasoning Type This section contains 2 Reasoning type questions. Each question has 4 choices (A), (B), (C) and (D), out of which ONLY ONE is correct. 13. Statement–1 : Z XA undergoes 2  decays, 2 decays (negative ) and 2  decays. As a result the daughter product is Z2 YA8 . Statement–2 : In  decay the mass number decreases by 4 unit and atomic number decreases by 2 unit. In  decay (negative ) the mass number remains unchanged and atomic number increases by 1 unit. In  decay, mass number and atomic number remains unchanged. (A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1 (B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (C) Statement-1 is True, Statement-2 is False (D) Statement-1 is False, Statement-2 is True. 14. Statement–1 : In the duration electron jumps from first excited state to ground state in a stationary isolated hydrogen atom, angular momentum of the electron about the nucleus is conserved. Statement–2 : As the electron jumps from first excited state to ground state, in a hydrogen atom, the electrostatic force on electron is always directed towards the nucleus. (A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1 (B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (C) Statement-1 is True, Statement-2 is False (D) Statement-1 is False, Statement-2 is True. SECTION - IV Comprehension Type This section contains 1 Paragraphs. Based upon each paragraph, 3 Multiple choice questions have to be answered. Each question has 4 choices (A), (B), (C) and (D), out of which ONLY ONE is correct. 15. A hydrogen atom in ground state passes through a magnetic field that has a gradient of 16mT/m in the vertical direction. If vertical component magnetic moment of the atom is 9.3 × 10–24 J/T, then force on it due to the magnetic moment of the electron is : (A) 5.8 × 10–22 N (B) 1.5 × 10–25 N (C) 5.8 × 10–24 N (D) 1.5 × 10–24 N → 16. In the Stern–Gerlach experiment conducted with silver atoms, the magnetic field B has a magnitude of 620 mT. If magnetic moment of a silver atom is 5.8 × 10–5 eV/T, then the energy difference between the orientation of the silver atoms in the two subbeams is : (A) 3.6 × 10–5 eV (B) 3.6 × 10–2 eV (C) 7.2 × 10–5 eV (D) 7.2 × 10–2 eV 17. In the previous question, the minimum frequency of radiation that may induce a transition between these two states is (h = 4.14 × 10–15 eV.s) : (A) 8.7 × 109 Hz (B) 3 × 1010 Hz (C) 6.2 × 1010 Hz (D) 1.74 × 1010 Hz SECTION - V Matrix - Match Type This section contains 1 questions. Each question has four statements (A, B, C and D) given in Column-I and five statements (p,q,r, s and t) in Column-II. Any given statement in Column-I can have correct matching with ONE OR MORE statement(s) in Column-II. The answers to these questions have to be appropriately marked as illustrated in the following example. If the correct matches are A-p, A-r, B-p, B-s, C-r, C-s, D-q and D-t then the answer should be written as : A  p,r ; B p, s ; C  r, s ; D  q, t. 18. In column-I, consider each process just before and just after it occurs. Initial system is isolated from all other bodies. Consider all product particles (even those having rest mass zero) in the system. Match the system in column-I with the result they produce in column-II. Column-I Column-II (A) Spontaneous radioactive decay of an (p) Number of protons is increased uranium nucleus initially at rest as given by reaction 238U  234Th  4He  ... 92 90 2 (B) Fusion reaction of two hydrogen nuclei (q) Momentum is conserved as given by reaction 1H  1H  2H  ..... 1 1 1 0 92 56 36 0 A nswers 1. (D) 2. (C) 3. (C) 4. (B) 5. (B) 6. (B) 7. (A) 8. (A) 9. (C) 10. (D) 11. (B,C) 12. (B,C) 13. (A) 14. (D) 15. (B) 16. (C) 17. (D) 18. A-qrst; B-qrs; C-qrs; D-pqrst 19. 3 20. 28 21. 6 22. 55