Tiêu đề 21.Magnetism and Matter Easy.pdf ✅

1. An iron rod of length L and magnetic moment M is bent in the form of a semicircle. Now its magnetic moment will be (a) M (b)  2M (c)  M (d) M 2. Unit of magnetic flux density (or magnetic induction) is (a) Tesla (b) Weber/metre2 (c) Newton/ampere-metre (d) All of the above 3. Magnetic intensity for an axial point due to a short bar magnet of magnetic moment M is given by (a) 3 0 4 d M    (b) 2 0 4 d M    (c) 3 0 2 d M    (d) 2 0 2 d M    4. A magnet is placed in iron powder and then taken out, then maximum iron powder is at (a) Some away from north pole (b) Some away from south pole (c) The middle of the magnet (d) The end of the magnet 5. A magnet of magnetic moment M and pole strength m is divided in two equal parts, then magnetic moment of each part will be (a) M (b) M / 2 (c) M / 4 (d) 2M 6. Points A and B are situated along the extended axis of 2 cm long bar magnet at a distance x and 2x cm respectively. From the pole nearer to the points, the ratio of the magnetic field at A and B will be (a) 4 : 1 exactly (b) 4 : 1 approx. (c) 8 : 1 exactly (d) 8 : 1 approx. 7. If a magnet of pole strength m is divided into four parts such that the length and width of each part is half that of initial one, then the pole strength of each part will be (a) m / 4 (b) m / 2 (c) m / 8 (d) 4m 8. The distance of two points on the axis of a magnet from its centre is 10 cm and 20 cm respectively. The ratio of magnetic intensity at these points is 12.5 : 1. The length of the magnet will be (a) 5 cm (b) 25 cm (c) 10 cm (d) 20 cm 9. The magnetism of magnet is due to (a) The spin motion of electron (b) Earth (c) Pressure of big magnet inside the earth (d) Cosmic rays 10. The pole strength of a bar magnet is 48 ampere-metre and the distance between its poles is 25 cm. The moment of the couple by which it can be placed at an angle of 30o with the uniform magnetic intensity of flux density 0.15 Newton /ampere-metre will be (a) 12 Newton × metre (b) 18 Newton × metre (c) 0.9 Newton × metre (d) None of the above 11. 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 distances 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 12. A magnet of magnetic moment 20 C.G.S. units is freely suspended in a uniform magnetic field of intensity 0.3 C.G.S. units. The amount of work done in deflecting it by an angle of 30o in C.G.S. units is (a) 6 (b) 3 3 (c) 3(2 − 3) (d) 3 13. A bar magnet having centre O has a length of 4 cm. Point P1 is in the broad side-on and P2 is in the end side-on position with OP1 = OP2 = 10 metres. The ratio of magnetic intensities H at P1 and P2 is (a) : 16 : 100 H1 H2 = (b) : 1 : 2 H1 H2 = (c) : 2 : 1 H1 H2 = (d) : 100 : 16 H1 H2 = 14. The magnetic field due to a short magnet at a point on its axis at distance X cm from the middle point of the magnet is 200 Gauss. The magnetic field at a point on the neutral axis at a distance X cm from the middle of the magnet is (a) 100 Gauss (b) 400 Gauss (c) 50 Gauss (d) 200 Gauss 15. Which of the following, the most suitable material for making permanent magnet is (a) Steel (b) Soft iron (c) Copper (d) Nickel 16. In the case of bar magnet, lines of magnetic induction (a) Start from the north pole and end at the south pole (b) Run continuously through the bar and outside (c) Emerge in circular paths from the middle of the bar (d) Are produced only at the north pole like rays of light from a bulb

29. If the magnetic flux is expressed in weber, then magnetic induction can be expressed in (a) Weber/m2 (b) Weber/m (c) Weber-m (d) Weber-m2 30. A magnetic needle is kept in a non-uniform magnetic field. It experiences (a) A force and a torque (b) A force but not a torque (c) A torque but not a force (d) Neither a torque nor a force 31. The magnetic induction in air at a distance d from an isolated point pole of strength m unit will be (a) d m (b) 2 d m (c) md (d) 2 md 32. A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60°. The torque required to maintain the needle in this position will be (a) 3 W (b) W (c) W 2 3 (d) 2W 33. A long magnetic needle of length 2L, magnetic moment M and pole strength m units is broken into two pieces at the middle. The magnetic moment and pole strength of each piece will be (a) 2 , 2 M m (b) 2 , m M (c) m M , 2 (d) M,m 34. Two identical thin bar magnets each of length l and pole strength m are placed at right angle to each other with north pole of one touching south pole of the other. Magnetic moment of the system is (a) ml (b) 2ml (c) 2ml (d) ml 2 1 35. Magnetic induction is a (a) Scalar quantity (b) Vector quantity (c) Both (a) and (b) (d) None of the above 36. What happens to the force between magnetic poles when their pole strength and the distance between them are both doubled (a) Force increases to two times the previous value (b) No change (c) Force decreases to half the previous value (d) Force increases to four times the previous value 37. Force between two unit pole strength placed at a distance of one metre is (a) 1 N (b) N 4 10 −7 (c) N 7 10 − (d) N 7 4 10 −   38. A small bar magnet of moment M is placed in a uniform field H. If magnet makes an angle of 30° with field, the torque acting on the magnet is (a) MH (b) 2 MH (c) 3 MH (d) 4 MH 39. If a hole is made at the centre of a bar magnet, then its magnetic moment will (a) Increase (b) Decrease (c) Not change (d) None of these 40. The small magnets each of magnetic moment 10 A-m2 are placed end-on position 0.1m apart from their centres. The force acting between them is (a) N 7 0.6  10 (b) N 7 0.06  10 (c) 0.6N (d) 0.06N 41. Magnetic lines of force (a) Always intersect (b) Are always closed (c) Tend to crowd far away from the poles of magnet (d) Do not pass through vacuum 42. Rate of change of torque  with deflection  is maximum for a magnet suspended freely in a uniform magnetic field of induction B, when (a)  = 0 (b)  = 45 (c)  = 60 (d)  = 90 43. A magnet of magnetic moment M is rotated through 360° in a magnetic field H, the work done will be (a) MH (b) 2MH (c) 2MH (d) Zero 44. The direction of line of magnetic field of bar magnet is (a) From south pole to north pole (b) From north pole to south pole (c) Across the bar magnet (d) From south pole to north pole inside the magnet and from north pole to south pole outside the magnet