Tiêu đề 21.Magnetism and Matter Medi.pdf ✅

1. The primary origin of magnetism lies in (a) Atomic current and intrinsic spin of electrons. (b) Polar and non polar nature of molecules. (c) Pauli exclusion principle. (d) Electronegative nature of materials. 2. If BE represents equatorial magnetic field and BA represents axial magnetic field due to a bar magnet. Which of the following relationships between BE and BA is correct? (a) BE = 2BA (b) BA = 2 BE (c) BE = 4 BA (d) BA = 4 BE 3. Which of the following is not correct about the magnetic field lines? (a) The magnetic field lines of a magnet form continuous closed loops. (b) The tangent to the field line at a given point represents the direction of the net magnetic field B at that point. (c) The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B. (d) The magnetic field lines may intersect to each other in certain conditions. 4. Which of the following is correct about magnetic monopole? (a) Magnetic monopole exist. (b) Magnetic monopole does not exist. (c) Magnetic monopole have constant value of monopole momentum. (d) The monopole momentum increase due to increase at its distance from the field. 5. The torque and magnetic potential energy of a magnetic dipole in most stable position in a uniform magnetic field ( B  ) having magnetic moment ( m  ) will be (a) -mB, zero (b) mB, zero (c) zero, mB (d) zero, -mB. 6. A solenoid of cross-sectional area 2 x 10~4 m2 and 900 turns has 0.6 A m2 magnetic moment. Then the current flowing through it is (a) 2.24 A (b) 2.34 m A (c) 3.33 A (d) 3.33 Ma 7. The work done in moving a dipole from its most stable to most unstable position in a 0.09 T uniform magnetic field is (dipole moment of this dipole = 0.5 A m2 ) (a) 0.07 J (b) 0.08 J (c) 0.09 J (d) 0.1 J 8. A magnetic needle has a magnetic moment 5.0 × 10-2 A m2 and moment of inertia 8.5 x 10-7 Kg m2 . It performs oscillation of time period 0.65 s. What is the magnitude of the magnetic field? (a) 0.0016 T (b) 0.16 T (c) 1.6 T (d) 16 T. 9. The magnitude of the equatorial magnetic field due to a bar magnet of length 2 cm at a distance of 1 m from its mid-point is (magnetic moment of the bar magnet is 2 0.60 A m ) (a) 5.0 x 10-5 T (b) 6.0xl0-8 T (c) 7.0 x 10-7 T (d) 8.0 x 10-8 T 10. What is the magnitude of axial field due to a bar magnet of length 3 cm at a distance of 75 cm from its mid-point if its magnetic moment is 0.6 A m2 ? (a) 0.013T (b) 0.113T (c) 0.213T (d) 0.313T 11. A short bar magnet placed with its axis at 30° with a uniform external magnetic field of 0.35 T experiences a torque of magnitude equal to 4.5 10-2 J. The magnitude of magnetic moment of the given magnet is (a) 26 J T-1 (b) 2.6 J T-1 (c) 0.26 J T-1 (d) 0.026 J T-1 12. A closely wound solenoid of 750 turns and area of cross section of 5 x 10-4 m2 carries a current of 3.0 A. Its associated magnetic moment is (a) 4.12 J T -1 (b) 3.12 J T-1 (c) 2.12 J T-1 (d) 1.13 J T -1 13. A circular coil of 25 turns and radius of 12 cm is placed in a uniform magnetic field of 0.5 T normal to the plane of coil. If the current in the coil is 5 A, then total torque experienced by the coil is (a) 1.5 Nm (b) 2.5 N m (c) 3.5 N m (d) Zero 14. A short bar magnet has a magnetic moment of 0.48 J T-1 . The magnitude and direction of magnetic field produced by the magnet at a distance of 10 cm from the centre of the magnet on its axis is (a) 0.48 × 10-4 along N-S direction (b) 0.28 × 10-4 T along S-N direction (c) 0.28 × 10-4 T along N-S direction (d) 0.96 × 10-4 T along S-N direction 15. A closely wound solenoid of 1000 turns and area of cross section 1.4 x 10-4 m2 carrying a current of 3 A is suspended through its centre allowing it to turn in a horizontal plane the magnetic moment associated with this solenoid is (a) 0.22 J T-1 (b) 0.32 J T-1 (c) 0.42 JT-1 (d) 0.52J-1 16. If a solenoid is having magnetic moment of 0.65 J T-1 is free to turn about the vertical direction and has a uniform horizontal magnetic field of 0.25 T applied. What is the magnitude of the
torque on the solenoid when its axis makes an angle of 30° with the direction of applied field? (a) 0.075 N m (b) 0.080 N m (c) 0.081 N m (d) 0.091 N m 17. A short bar magnet has a magnetic moment of 0.39 J T-1 . The magnitude and direction of the magnetic field produced by the magnet at a distance of 20 cm from the centre of the magnet on the equatorial line of the magnet is (a) 0.049 G, N-S direction (b) 4.95 G, S-N direction (c) 0.0195 G, S-N direction (d) 19.5 G, N-S direction 18. Which of the following is not showing the essential difference between electrostatic shielding by a conducting shell and magneto static shielding? (a) Electrostatic field lines can end on charges and conductors have free charges. (b) Magnetic field lines can end but conductors cannot end them. (c) Lines of magnetic field cannot end on any material and perfect shielding is not possible. (d) Shells of high permeability materials can be used to divert lines of magnetic field from the interior region. 19. The magnetic induction at a point 1 o A away from a proton measured along its axis of spin is (magnetic moment of the proton is 1.4 x l0-26 A m2 ) (a) 0.28 mT (b) 28 mT (c) 0.028 mT (d) 2.8 mT 20. A wire is placed between the poles of two fixed bar magnets as shown in the figure. A small current in the wire is into the plane of the paper. The direction of the magnetic force on the wire is (a)  (b)  (c) → (d)  21. A circular coil of 300 turns and diameter 14 cm carries a current of 15 A. The magnitude of magnetic moment associated with the loop is (a) 51.7 JT-1 (b) 69.2 JrT1 (c) 38.6 JT-1 (d) 19.5 JT-1 22. The pole strength of 12 cm long bar magnet is 20 A m. The magnetic induction at a point 10 cm away from the centre of the magnet on its axial line is       =  0 −7 −1 10 H m 4 (a) 1.17 x 10-3 T (b) 2.20 10 T −3  (c) 1.17 x 10-2 T (d) 2.20 10 T −2  23. A current carrying loop is placed in a uniform magnetic field in four different orientations as shown in figure. Arrange them in the decreasing order of potential energy. (a) 4,2,3,1 (b) 1,4,2,3 (c) 4,3,2,1 (d) 1,2,3,4 24. A long solenoid has 1000 turns per metre and carries a current of 1 A. It has a soft iron core of ( r = 1000. The core is heated beyond the Curie temperature Tc . (a) The H field in the solenoid is (nearly) unchanged but B field decreases drastically. (b) The H and B fields in the solenoid are nearly uncharged. (c) The magnetisation in the core reverses direction. (d) The H field in the solenoid decreases but B field increases drastically. 25. A bar magnet of magnetic moment M and moment of inertia I (about centre perpendicular to length) is cut into two equal pieces perpendicular to length. Let T be the period of oscillations of the original magnet about an axis through the midpoint perpendicular to length in magnetic field B. The similar period T’ for each piece would be (a) 2 T (b) 4 3T (c) 2 5T (d)T 26. There are two current carrying planar coils made each from identical wires of length L. C is circular (radius R) and C2 is square (side a). They are so constructed that they have same frequencies of oscillation when they are placed in the same uniform magnetic field B and carry the same current I. The relation between a and R is (a) a = 2R (b) a = 3R (c) 3a = R (d) a = 4R 27. A dipole of magnetic moment m  30 2 ˆ j A m is placed along they-axis in a uniform magnetic field B = (2i + 5j)T. The torque acting on it is (a) − 40 k ˆ N m (b) − 50 k ˆ N m (c) − 60 k ˆ Nm (d) − 70k ˆ N m 28. A closely wound solenoid of 3000 turns and area of cross section 2 x 10-4 m2 , carrying a current of 6 A is suspended through its centre allowing it to turn in a horizontal plane. The magnetic moment associated with this solenoid is (a) 1 1.2 J T − (b) 1 2.4 J T − (c) 1 3.0J T − (d) 1 3.6 J T −
29. A uniform horizontal magnetic field of 7.5 x 10-2 T is set up at an angle of 30° with the axis of an solenoid and the magnetic moment associated with it is 1.28 J T-1 . Then the torque on it is (a) 4.8 x 10-2 N m (b) 1.6x10-2N m (c) 1.13 x 10-2 kg m (d) 4.8 x 10-4 N m 30. A circular coil of magnetic moment 0.355 J T-1 rests with its plane normal to an external field of magnitude 5.0 x 10-2 T. The coil is free to turn about an axis in its plane perpendicular to the field direction. When the coil is turned slightly and released, it oscillates about its stable equilibrium with a frequency of 2 Hz. The moment of inertia of the coil about its axis of rotation is (a) 1.13 x 10-1 kg m2 (b) 2 2 1.13 10 kg m −  (c) 3 2 1.13 10 kgm −  (d) 4 2 1.13 10 kg m −  31. A magnetic dipole is under the influence of two magnetic fields. The angle between the field directions is 60° and one of the fields has a magnitude of 1.2 x 10-2 T. If the dipole comes to stable equilibrium at an angle of 30° with this field, then the magnitude of the field is (a) 1.2 x 10-4 T (b) 2.4 x 10-2 T (c) 1.2 10 T −2  (d) 2.4 10 T −2  32. Two short bar magnets of magnetic moments m each are arranged at the opposite corners of a square of side d such that their centres coincide with the corners and their axes are parallel. If the like poles are in the same direction, the magnetic induction at any of the other corners of the square is (a) 3 0 d m 4  (b) 3 0 d 2m 4  (c) 3 0 2d m 4  (d) 3 3 0 2d m 4  33. Point out the correct direction of magnetic field in the given figures. (a) (b) (c) (d) 34. The earth behaves as a magnet with magnetic field pointing approximately from the geographic (a) North to South (b) South to North (c) East to West (d) West to East 35. The strength of the earths magnetic field is (a) Constant everywhere (b) Zero everywhere (c) Having very high value (d) Vary from place to place on the earths surface 36. The equatorial magnetic field of earth is 0.4 G. Then its dipole moment on equator is (a) 1.05 x 1023 A m2 (b) 2.05 x 1023 Am2 (c) 1.05 x 1021 Am2 (d) 2.05 x l021Am2 37. In the magnetic meridian of a certain place the horizontal component of earth’s magnetic field is 0.25 G and dip angle is 60°. The magnetic field of the earth at this location is (a) 0.50 G (b) 0.52 G (c) 0.54 G (d) 0.56 G 38. The dip angle at a location in southern India is about 18°. Then the dip angle in Britain will be (a) Greater than 18° (b) Lesser than 18° (c) Equal to 18° (d) Zero 39. At a certain location in Africa, compass points 12° west of geographic north. The north tip of magnetic needle of a dip circle placed in the plane of magnetic meridian points 60° above the horizontal. The horizontal component of earth’s field is measured to be 0.16 G. The magnitude of earth’s field at the location is (a) 0.32 G (b) 0.42 G (c) 4.2 G (d) 3.2 G 40. A compass needle whose magnetic moment is 60 A m2 pointing geographical north at a certain place where the horizontal component of earths magnetic field is 40 x 10-6 Wb m-2 experiences a torque of 1.2 x 10-3 N m. The declination of the place is (a) 20° (b) 45° (c) 60° (d) 30° 41. Let the magnetic field on earth be modelled by that of a point magnetic dipole at the centre of earth. The angle of dip at a point on the geographical equator is (a) Always zero (b) Positive, negative or zero (c) Unbounded (d) Always negative 42. The vertical component of earths magnetic field at a place is 3 times the horizontal component the value of angle of dip at this place is (a) 30° (b) 45° (c) 60° (d) 90° 43. Consider the plane S formed by the dipole axis and the axis of earth. If P be the point of intersection of the geographical and magnetic equators then the declination and dip angle at point P are (a) 0°, 11.3° (b) 11.3°, 0° (c) 11.3°, 11.3° (d) 0°, 0° 44. The angles of dip at the poles and the equator respectively are (a) 30°, 60° (b) o o 0 ,90
(c) 45°, 90° (d) o o 90 ,0 45. At a given place on earth’s surface the horizontal component of earths magnetic field is 2 x 10-5 T and resultant magnetic field is 4 x 10-5 T. The angle of dip at this place is (a) 30° (b) 60° (c) o 90 (d) o 45 46. The earth’s field departs from its dipole shape substantially at large distance (greater than about 3000 Km). The responsible factor for this distortion is (a) Motion of ions in earth’s ionosphere (b) Motion of ions in earth’s atmosphere (c) Motion of ions in earth’s lithosphere (d) Motion of ions in the space. 47. A vector needs three quantities for its specification. Which of the following independent quantities is not used to specify the earth’s magnetic field? (a) Magnetic declination (  ). (b) Magnetic dip (  ). (c) Horizontal component of earths field (BH ). (d) Vertical component of earth’s field (Bv ). 48. If you made a map of magnetic field lines at melbourne in Australia, then the magnetic field lines seem to be (a) Go into the ground (b) Come out of the ground (c) Maintain a spiral path on the surface of earth (d) Move on helical path above the surface of ground 49. The angle of dip at a certain place where the horizontal and vertical components of the earth’s magnetic field are equal is (a) 30° (b) 75° (c) 60° (d) 45° 50. Which of the following is responsible for the earth’s magnetic field? (a) Convective currents in earth’s core. (b) Diversive current in earth’s core. (c) Rotational motion of earth. (d) Translational motion of earth. 51. A solenoid has a core of a material with relative permeability of 500. The windings of the solenoid are insulated from the core and carry a current of 2 A. If the number of turns is 1000 per meter, then magnetisation is (a) 7.78 x 105 A m-1 (b) 8.88xl05Am-1 (c) 9.98 x 105 A m-1 (d) 10.2 x 10s A m-1 52. A circular coil of 25 turns and radius of 20 cm carrying a current of 1 A rests with its plane normal to an external field of magnitude 5.0 x 10-2 T. The coil is free to turn about an axis in its plane perpendicular to the field direction. When the coil is turned slightly and released its oscillates about its stable equilibrium with a frequency of 2 s-1 . The moment of inertia of the coil about its axis of rotation (a) 2.4 x 10-4 kg m2 (b) 1.2x10-4 kg m2 (c) 9.95 x 10-4 kg m2 (d) 9.25 x 10-4 kg m2 53. A permanent magnet in the shape of a thin cylinder of length 10 cm has magnetisation (M) = 106 A m-1 . It’s magnetization current IM is (a) 105A (b) 106A (c) 107A (d) 108A 54. Which of the following is not correct about relative magnetic permeability ( )? r (a) It is a dimensionless pure ratio. (b) For vacuum medium its value is one. (c) For ferromagnetic materials 1 r   (d)For paramagnetic materials 1 r  55. A permanent magnet in the shape of a thin cylinder of length 50 cm has intensity of magnetisaton 106 m-1 . The magnetisation current is (a) 5 x 105 A (b) 6 x 10s A (c) 5 x 104 A (d) 6 x 104 A 56. A solenoid has a core of a substance with relative permeability 600. What is the magnetic permeability of the given substance? (a) 20  10-5NA-2 (b) 21  10-5 N A-2 (c) 22  10-5 N A-2 (d) 24  10-5 N A-2 57. A domain in ferromagnetic iron in the form of cube is having 5 x 1010 atoms. If the side length of this domain is 1.5  m and each atom has a dipole moment of 8 × 10-24 A m2 , then magnetisation of domain is (a) 11.8 x 105 Am-1 (b) 1.18 x 104Am-1 (c) 11.8 x 104 A m_1 (d) 1.18 x 10s A m-1 58. A ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. The magnetic field in the core for a magnetising current of 1.2 A is (a) 2.48 T (b) 3.48 T (c) 4.48 T (d) 5.48 T 59. A thin magnetic needle oscillates in a horizontal plane with a period T. It is broken into n equal parts. The time period of each part will be (a) nT (b) n 2T (c) n T (d) 2 n T 60. A magnetising field of 2 x 103 A m-1 produces a magnetic flux density of 8  T in an iron rod. The relative permeability of the rod will be (a) 102 (b) 1 (c) 4 10 (d) 3 10 61. A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of