Title 21.Magnetism and Matter Hard.pdf ✅

1. Two identical magnetic dipoles of magnetic moments 1.0 A- m2 each, placed at a separation of 2m with their axis perpendicular to each other. The resultant magnetic field at a point midway between the dipoles is (a) T 7 5 10 −  (b) T 7 5 10 −  (c) 2 T (d) None 2. The magnetic field at a point X on the axis of a small bar magnet is equal to the field at a point Y on the equator of the same magnet. The ratio of the distance of X and Y from the centre of the magnet is (a) 3 2 − (b) 1 / 3 2 − (c) 3 2 (d) 1 / 3 2 3. At a place the earth's horizontal component of magnetic field is 0.38 10 / . 4 2 weber m −  If the angle of dip at that place is 600 , then the vertical component of earth's field at that place in weber/m2 will be approximately (a) 4 0.12 10 −  (b) 4 0.24 10 −  (c) 4 0.40 10 −  (d) 4 0.62 10 −  4. A dip circle is so set that it moves freely in the magnetic meridian. In this position, the angle of dip is 400 . Now the dip circle is rotated so that the plane in which the needle moves makes an angle of 300 with the magnetic meridian. In this position, the needle will dip by the angle (a) 400 (b) 300 (c) More than 400 (d) Less than 400 5. Earth's magnetic field may be supposed to be due to a small bar magnet located at the centre of the earth. If the magnetic field at a point on the magnetic equator is 0.3×10–4 T. Magnet moment of bar magnet is (a) 8 2 7.8 10 amp  m (b) 22 2 7.8 10 amp m (c) 22 2 6.4 10 amp  m (d) None of these 6. A short bar magnet is placed with its south pole towards geographical north. The neutral points are situated at a distance of 20 cm from the centre of the magnet. If 4 2 BH 0.3 10 wb / m − =  then the magnetic moment of the magnet is (a) 9000 ab-amp × cm2 (b) 900 2 ab − amp  cm (c) 2 1200 ab − amp  cm (d) 2 225 ab − amp  cm 7. Two magnets of equal mass are joined at right angles to each other as shown the magnet 1 has a magnetic moment 3 times that of magnet 2. This arrangement is pivoted so that it is free to rotate in the horizontal plane. In equilibrium what angle will the magnet 1 subtend with the magnetic meridian (a)      −  2 1 tan 1 (b)      −  3 1 tan 1 (c) tan (1) −1 (d) 00 8. Two magnets are held together in a vibration magnetometer and are allowed to oscillate in the earth's magnetic field. With like poles together 12 oscillations per minute are made but for unlike poles together only 4 oscillations per minute are executed. The ratio of their magnetic moments is (a) 3 : 1 (b) 1 : 3 (c) 3 : 5 (d) 5 : 4 9. In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal component of earth's magnetic field is 2 sec. When a magnet is brought near and parallel to it, the time period reduces to 1 sec. The ratio H/F of the horizontal component H and the field F due to magnet will be (a) 3 (b) 3 1 (c) 3 (d) 3 1 10. A certain amount of current when flowing in a properly set tangent galvanometer, produces a deflection of 4500 . If the current be reduced by a factor of 3, the deflection would (a) Decrease by 300 (b) Decreases by 150 (c) Increase by 150 (d) Increase by 300 11. The angle of dip at a place is 60o . A magnetic needle oscillates in a horizontal plane at this place with period T. The same needle will oscillate in a vertical plane coinciding with the magnetic meridian with a period (a) T (b) 2T (c) 2 T (d) 2 T 12. A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds.The same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds. Then the angle of dip is (a) 00 (b) 300 (c) 450 (d) 900 13. A ferromagnetic substance of volume 10–3m3 is placed in an alternating field of 50 Hz. Area of hysteresis curve obtained is 0.1 M.K.S. unit. The heat produced due to energy loss per second in the substance will be (a) 5 J (b) 5  10–2 cal (c) 1.19  10–3 cal (d) No loss of energy 14. A magnetising field of 1600 A-m–1 produces a magnetic flux of 2.4  10–5Wb in an iron bar of cross-sectional area 0.2 cm2 . The susceptibility of an iron bar is 90° (1) (2) m1  S N N S m2 r = 20 cm N1 N E S W N S r = 20 cm N2 R S Magneticeq uator N
(a) 298 (b) 596 (c) 1192 (d) 1788 15. For iron it's density is 7500 kg/m3 and mass 0.075 kg. If it's magnetic moment is 8  10–7Ampm2 , it's intensity of magnetization is (a) 8 Amp/m (b) 0.8 Amp/m (c) 0.08 Amp/m (d) 0.008 Amp/m 16. The dipole moment of each molecule of a paramagnetic gas is 1.5  10–23Ampm2 . The temperature of gas is 27oC and the number of molecules per unit volume in it is 2  1026m–3 . The maximum possible intensity of magnetization in the gas will be (a) 3  103Amp/m (b) 4  10–3Amp/m (c) 5  105Amp/m (d) 6  10–4Amp/m 17. The coereivity of a small bar magnet is 4  103Amp/m. It is inserted inside a solenoid of 500 turns and length 1 m to demagnetise it. The amount of current to be passed through the solenoid will be (a) 2.5 A (b) 5 A (c) 8 A (d) 10 A 18. A uniform but time varying magnetic field exists in cylindrical region and directed into the paper. If field decrease with time and a positive charge placed at any point inside the region. Then it moves - × × × × × × × × 3 2 4 1 C P (a) Along 1 (b) Along 2 (c) Along 3 (d) Along 4 19. Two small pith balls, each carrying a charge q are attached to the ends of a light rod of length d, which is suspended from the ceiling by a thin torsion free fiber as shown in figure. There is a uniform magnetic field B pointing straight down, in the cylindrical region of radius R around the fiber. The system is initially at rest. If the magnetic field is turned off. Which of the following happen to the system - B field region fiber q q R (a) It rotate with an angular momentum qBR2 (b) It does not move at all (c) It rotate with an angular momentum 2 qBR 2 (d) None of the above[C] 20. In given figure, a wire loop has been bent so that it has three segments ab (a quarter circle), bc (a square corner) &ca (straight line). Here are three choices for a magnetic field through the loop– a a a z x y c b a (1) → B1 = i ˆ 3 + j ˆ 7 – k ˆ 5t (2) → B2 = i ˆ 5t – j ˆ 4 – k ˆ 15 (3) → B3 = i ˆ 2 – j ˆ 5t – k ˆ 12 Where B is in millitesllas and t is in second if the induced current in the loop due to → B1 , → B2 , → B3 are i1, i2, i3 respectively then - (a) i1> i2> i3 (b) i2> i1> i3 (c) i3> i2> i1 (d) i1 = i2 = i3 21. Two magnets each of magnetic moment M are placed so as to form a cross at right angle to each other. Magnetic moment of the system will be - (a) 2 M (b) M 2 (c) M/2 (d) M 2 22. The ratio of magnetic potentials due to magnetic dipole in the end-on position to that in the broad side on position for the same distance from it is - (a) Zero (b) 1 (c) 2 (d)  23. A specimen of iron of permeability 8 × 10–3 Weber/amp × metre is placed in a magnetic field of strength 160 amp/meter. Then magnetic induction in this iron is - (a) 20 × 103 wb/m2 (b) 1.28 wb/m2 (c) 5 × 10–5 wb/m2 (d) 0.8 wb/m2 24. A ferromagnetic material is placed in an external magnetic field. The size of magnetic domains - (a) Decreases only (b) Increases only (c) Sometimes increases and sometimes decreases (d) Remains unchanged only 25. A compass needle placed at a distance r from a short magnet in tanA position shows a deflection of 600 . If the distance is increased to r(3)1/3, then the deflection of the compass needle is - (a) 300 (b) 600 × (3)1/3 (c) 600 × (3)2/3 (d) 600 × (3)3/3 26. A magnetic needle of negligible breadth and thickness compared to its length, oscillates in a horizontal plane with a period T. The period of oscillation of each part obtained on
breaking the magnet into n equal parts and perpendicular to the length is - (a) T (b) T/n (c) Tn (d) 1Tn 27. The tangent galvanometers having coils of the same radius are connected in series. A current flowing in them produces deflections of 600 and 450 respectively. The ratio of the number of turns in the coil is - (a) (4/3) (b) ( 3 + 1)/1 (c)         + 3 –1 3 1 (d) 3 /1 28. Two identical short bar magnets each having magnetic moment M are placed at a distance of 2d with their axes ⊥ to each other in a horizontal plane. The magnetic induction at a point midway between them is - (a) 3 0 d M2 4  (b) 3 0 d M ( 3) 4  (c) 3 0 d M 4 2         (d) 3 0 d M ( 5) 4  29. There is magnetic material of coercivity 2 × 103 A/m. What current should flow through solenoid of length 15 cm having 150 turns to demagnetise the substance completely? (a) 4 A (b) 2.5 A (c) 2 A (d) 3.5 A 30. A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current I passes through the coil, the magnetic field at the centre is- (a) b NI 0 (b) a 2 NI 0 (c) 2(b – a) NI 0 log a b (d) 2(b – a) 0 IN log b a 31. When a magnet is suspended at an angle 300 from the magnetic meridian, it makes an angle 45o with horizontal. What will be the actual angle of dip? (a) tan–1         2 3 (b) tan–1 ( 3) (c) 450 (d) 300 32. The magnetic needle of a vibration magnetometer makes 12 oscillations per minute in the horizontal component of earth's magnetic field. When an external short bar magnet is placed at some distance along the axis of the needle in the same line, it makes 15 oscillations per minute. If the poles of the bar magnet are interchanged, the number of oscillations it makes per minute is- (a) 61 (b) 63 (c) 65 (d) 67 33. A magnetising field of 2000 A/m produces a flux 4 6.28 10 −  weber in a rod. If the area of cross-section is 2 10 . 5 2 m −  Then the relative permeability of the substance is (a) 2 0.75 10 −  (b) 4 1.25 10 (c) 0.25 (d) 1.01 34. Due to a small magnet intensity at a distance x in the end on position is 9 Gauss. What will be the intensity at a distance 2 x on broad side on position (a) 9 Gauss (b) 4 Gauss (c) 36 Gauss (d) 4.5 Gauss 35. The magnetic moment produced in a substance of 1gm is 6 10 . 7 2  ampere −metre − If its density is 5 / , 3 gm cm then the intensity of magnetisation in A/m will be (a) 6 8.3 10 (b) 3.0 (c) 7 1.2 10 −  (d) 6 3 10 −  36. The distance between the poles of a horse shoe magnet is 0.1 m and its pole strength is 0.01 amp-m. The induction of magnetic field at a point midway between the poles will be (a) T 5 2 10 −  (b) T 6 4 10 −  (c) T 7 8 10 −  (d) Zero 37. A cylindrical rod magnet has a length of 5 cm and a diameter of 1 cm. It has a uniform magnetisation of 5.30 × 103Amp/m3 . What its magnetic dipole moment (a) 1 10 J / T −2  (b) 2.08 10 J / T −2  (c) 3.08 10 J / T −2  (d) 1.52 10 J / T −2  38. A bar magnet has a magnetic moment of 1 2.5 − JT and is placed in a magnetic field of 0.2T. Work done in turning the magnet from parallel to anti-parallel position relative to field direction is (a) 0.5J (b) 1J (c) 2J (d) 0 J 39. A bar magnet with it's poles 25 cm apart and of pole strength 24 amp×m rests with it'scentre on a frictionless pivot. A force F is applied on the magnet at a distance of 12 cm from the pivot so that it is held in equilibrium at an angle of 30° with respect to a magnetic field of induction 0.25 T. The value of force F is (a) 5.62 N (b) 2.56 N (c) 6.52 N (d) 6.25 N 40. Two identical bar magnets with a length 10 cm and weight 50 gm – weight are arranged freely with their like poles facing in a arranged vertical glass tube. The upper magnet hangs in the air above the lower one so that the distance between the nearest pole of the magnet is 3mm. Pole strength of the poles of each magnet will be (a) 6.64 amp m (b) 2 amp m (c) 10.25 amp m (d) None of these 41. If the angles of dip at two places are 300 and 450 respectively, Then the ratio of horizontal components of earth's magnetic field at the two places will be (a) 3 : 2 (b) 1: 2 (c) 1: 3 (d) 1 : 2 N S S N
42. The magnetic needle of a tangent galvanometer is deflected at an angle 300 due to a magnet. The horizontal component of earth's magnetic field 0.34×10–4T is along the plane of the coil. The magnetic intensity is (a) T 4 1.96 10 −  (b) T 5 1.96 10 −  (c) T 4 1.96 10 (d) T 5 1.96 10 43. A magnet freely suspended in a vibration magnetometer makes 10 oscillations per minute at a place A and 40 oscillations per minute at a place B. If the horizontal component of earth's magnetic field at A is 36 10 , 6 T −  then its value at B is (a) T 6 36 10 −  (b) T 6 72 10 −  (c) T 6 144 10 −  (d) T 6 288 10 −  44. The magnet of a vibration magnetometer is heated so as to reduce its magnetic moment by 19%. By doing this the periodic time of the magnetometer will (a) Increase by 19% (b) Increase by 11% (c) Decrease by 19% (d) Decrease by 21% 45. A magnet makes 40 oscillations per minute at a place having magnetic field intensity 5 0.1 10 − BH =  . At another place, it takes 2.5 sec to complete one-vibration. The value of earth's horizontal field at that place (a) T 6 0.25 10 −  (b) T 6 0.36 10 −  (c) T 8 0.66 10 −  (d) T 6 1.2 10 −  46. When 2 amp. current is passed through a tangent galvanometer, it gives a deflection of 30°. For 60° deflection, The current must be (a) 1 amp. (b) 2 3 amp. (c) 4 amp. (d) 6 amp. 47. In vibration magnetometer the time period of suspended bar magnet can be reduced by (a) Moving it towards south pole (b) Moving it towards north pole (c) Moving it toward equator (d) Any one them 48. The time period of a freely suspended magnet is 2 sec. If it is broken in length into two equal parts and one part is suspended in the same way, then its time period will be (a) 4 sec (b) 2 sec (c) 2 sec (d) 1 sec 49. A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30o and 15 oscillations per minute at a place where dip angle is 60o . The ratio of total earth's magnetic field at the two places is (a) 3 3 : 8 (b) 16 : 9 3 (c) 4 : 9 (d) 2 3 : 9 50. If 1 and 2 are the deflections obtained by placing small magnet on the arm of a deflection magnetometer at the same distance from the compass box in tan A and tan B positions of the magnetometer respectively then the value of 2 1 tan tan   will be approximately (a) 1 (b) 2 (c) 2 1 (d) 2 51. The units for molar susceptibility (a) m 3 (b) kg-m –3 (c) kg–1m 3 (d) No units 52. The ratio of the area of B-H curve and I-H curve of a substance in M.K.S. system is (a) 2 0 (b) 2 0 1  (c) 0 (d) 0 1  53. If the magnetic lines of force are shaped like arcs of concentric circles with their centre at point O in a certain section of a magnetic field: O (a) The intensity of the field in this section should at each point be inversely proportional to its distance from point O (b) The intensity of the field in this section should at each point be inversely proportional to square of its distance from point O (c) The intensity of the field in this section should at each point be inversely proportional to cube of its distance from point O (d) Nothing can be said 54. A magnet is suspended horizontally in the earth's magnetic field. When it is displaced and released, it oscillates in a horizontal plane with a period T. If a piece of wood of same M.I as the magnet is attached to the magnet is attached to the magnet, the new period of oscillation of the system would be - (a) 3 T (b) 2 T (c) 2 T (d) 2T 55. A short magnet produces a deflection of 30° when placed at certain distance in tanA position of magnetometer. If another short magnet of double the length and thrice the pole strength is placed at the same distance in tanB position of the magnetometer, the deflection produced will be – (a) 600 (b) 300 (c) 450 (d) None 56. If a Bismuth rod is introduced in the air coil as shown then current in the coil - ~ V= 10 sin t