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5.MAGNETISM AND MATTER Single Correct Answer Type 1. Magnetic intensity for an axial point due to a short bar magnet of magnetic moment M is given by a) μ 0 4π × M d 3 b) μ 0 4π × M d 2 c) μ 0 2π × M d 3 d) μ 0 2π × M d 2 2. To measure which of the following , is a tangent galvanometer used a) Charge b) Angle c) Current d) Magnetic intensity 3. A long magnet is placed vertically with its S −pole resting on the table. A neutral point is obtained 10 cm from the pole the geographic north of it. If H = 3. 2×10 T ,then the pole strength of magnet is −5 a) 8 ab-A-cm −1 b) 16 ab-A-cm −1 c) 32 ab-A-cm −1 d) 64 ab-A-cm −1 4. The magnetic moment of a magnet of length 10 cm and pole strength 4. 0 Am will be a) 0.4 Am 2 b) 1.6 Am 2 c) 20 Am 2 d) 8.0 Am 2 5. Two magnets held together in earth’s magnetic field with same polarity together make 12 vib − and when opposite poles together make 4 vib − The ratio of magnetic moments is a) 9 :1 b) 1 : 3 c) 1 : 9 d) 10 : 8 6. In which direction, the magnetic field on the axis at a distance z from the centre of the bar magnet would be? a) In the perpendicular direction of the magnetic moment (M) of the magnet b) In the direction of the magnetic dipole moment (M) of the magnet c) Its direction depends on the magnitude of the magnetic moment (M) of the magnet d) In the opposite direction of the magnetic dipole moment(M) of the magnet 7. Two short magnets have equal pole strengths but one is twice as long as other. The shorter magnet is placed 20 cm in tan Aposition from the compass needle. The longer magnet must be placed on the other side of the magnetometer for no deflection at a distance equal to a) 20 cm b) 20×(2) 1/3 cm c) 20×(2) 2/3 cm d) 20×(2)cm 8. Electromagnets are made of soft iron because soft iron has a) Low susceptibility and low retentivity b) Low susceptibility and high retentivity c) High permeability and low retentivity d) High permeability and high coercivity 9. A long magnet is cut into two equal parts, such that the length of each half is same as that of original magnet. If the period of original magnetic is T, the period of new magnet is a) T b) T 2 c) T 4 d) 2T 10. If the B − H curves of two samples of Pand Q of iron are as shown below, then which one of the following statements is correct? Page| 1
a) Both P and Q are suitable for making permanent magnet b) Pis suitable for making permanent magnet and Q for making electromagnet c) Pis suitable for making electromagnet and Qis suitable for permanent magnet d) Both Pand Qare suitable for making electromagnets 11. A short magnetic needle is pivoted in a uniform magnetic field of strength 1 T. When another magnetic field of strength 3T is applied to the needle in a perpendicular direction, the needle deflects through an angle θ, where θ is a) 30° b) 45° c) 90° d) 60° 12. The magnetic susceptibility does not depend upon the temperature in a) Ferrite substances b) Ferromagnetic substances c) Diamagnetic substances d) Paramagnetic substances 13. The area of hysteresis loop of a material is equivalent to 250 joule. When 10 kg material is magnetized by an alternating field of 50 Hz then energy lost in one hour will be (density of material is 7. 5 gm/cm ) 3 a) 6×10 4 J b) 6×10 4 erg c) 3×10 2 J d) 3×10 2 erg 14. A magnetic dipole is placed in two perpendicular magnetic fields B and and is in equilibrium taking → H → angle θwith B. Then → a) B = H b) B cosθ = H sin sin θ c) B sin sin θ = H cos cos d) B = H tan tan θ 15. Keeping dissimilar poles of two magnets of equal pole strength and length same side, their time period will be a) Zero b) One second c) Infinity d) Any value 16. When two magnetic moments are compared using equal distance method the deflections produced are 45° and 30°. If the length of magnets are in the ratio 1 : 2, the ratio of their pole strength is a) 3 : 1 b) 3 : 2 c) 3 : 1 d) 2 3 : 1 17. If a magnetic dipole of dipole moment M rotated through an angle θ with respect to the direction of the field H, then the work done is a) MH sin sin θ b) MH(1 − sin sin θ ) c) MH cos cos θ d) MH(1 − cos cos θ ) 18. The radius of the coil of a tangent galvanometer which has 10 turns is 0.1 m. The current required to produce a deflection of 60° B is H = 4×10 −5 ( T) a) 3 A b) 1.1 A c) 2.1 A d) 1.5 A 19. At a temperature of 30° C, the susceptibility of a ferromagnetic material is found to be X. Its susceptibility at 333° C is Page| 2
a) X b) 0. 5 X c) 2 X d) 0. 09 X 20. Magnetic moment of bar magnet is M. The work done to turn the magnet by 90° of magnet in direction of magnetic field Bwill be a) Zero b) 1 2 MB c) 2 MB d) MB 21. Two identical short bar magnets, each having magnetic moment of 10 Am , are arranged such that their 2 axial lines are perpendicular to each other and their centres be along the same straight line in a horizontal plane. If the distance between their centres is 0. 2 m, the resultant magnetic induction at a point midway between them is (μ 0 = 4π×10 −7Hm −1 ) a) 2 × 10 −7 tesla b) 5 × 10 −7 tesla c) 2 × 10 −3 tesla d) 5 × 10 −3 tesla 22. Relative permeability of iron is 5500, then it magnetic susceptibility will be a) 5500×10 7 b) 5500×10 −7 c) 5501 d) 5499 23. A very small magnet is placed in the magnetic meridian with its south pole pointing north. The null point is obtained 20 cm away from the centre of the magnet. If the earth’s magnetic field (horizontal component) at this point is 0. 3 gauss, the magnetic moment of the magnet is a) 8. 0×10 2 e. m. u b) 1. 2×10 3 e. m. u c) 2. 4×10 3 e. m. u d) 3. 6×10 3 e. m. u 24. Hysteresis loss is minimized by using a) Alloy of steel b) Shell type of core c) Thick wire which has low resistance d) Mu metal 25. A magnet of length 0.1 m and pole strength 10 A-m is kept in a magnetic field of 30 Wb at an angle −4 m −2 30°. The couple acting on it is ........× 10 Nm. −4 a) 7.5 b) 3.0 c) 4.5 d) 1.5 26. If the angular momentum of an electron is Jthen the magnitude of the magnetic moment will be → a) eJ m b) eJ 2m c) eJ 2m d) 2m eJ 27. A deflection magnetometer is adjusted in the usual way. When a magnet is introduced, the deflection observed is θ, and the period of oscillation of the needle in the magnetometer is T. When the magnet is removed, the period of oscillation is T .Find the relation between is 0 T andT 0 a) T 2 = T 0 2 cos θ b) T = T cos 0 θ c) T = T 0 cosθ d) T 2 = T 0 2 cosθ 28. 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) M 2 , m 2 b) M, m 2 c) M 2 , m d) M, m 29. A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1A. The number of turns of the solenoid is 500 per metre. The magnetization of the material is nearly a) 2. 5×10 3 Am −1 b) 2. 5×10 5 Am −1 c) 2. 0×10 3 Am −1 d) 2. 0×10 5 Am −1 Page| 3
30. Two short magnets with their axes horizontal and perpendicular to the magnetic meridian are placed with their centres 40 cm east and 50 cm west of magnetic needle. If the needle remains undeflected, the ratio of their magnetic moments M is 1 : M 2 a) 4 : 5 b) 16 : 25 c) 64 : 125 d) 2 : 5 31. The lines of force due to earth’s horizontal component of magnetic field are a) Parallel straight lines b) Concentric circles c) Elliptical d) Parabolic 32. The coil in a tangent galvanometer is 16 cm in radius. If a current of 20 mA is to produce a deflection of 45° then the number of turns wound on it, is (Take horizontal component of earth’s magnetic field = 0. 36×10 ) −4 T and μ 0 = 4π×10 −7Wb A −1 m −1 a) 229 b) 458 c) 689 d) 916 33. A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It a) Will become rigid showing no movement b) Will stay in any position c) Will stay in north-south direction only d) Will stay in east-west direction only 34. The magnetic moment of a diamagnetic atom is a) Much greater than one b) 1 c) Between zero and one d) Equal to zero 35. A tangent galvanometer has a coil with 50 turns and radius equal to 4 cm. A current of 0. 1 A is passing through it. The plane of the coil is set parallel to the earth’s magnetic meridian. If the value of the earth’s horizontal component of the magnetic field is 7×10 and , then the −5 tesla μ 0 = 4π×10 −7 weber/amp×m deflection in the galvanometer needle will be a) 45° b) 48. 2° c) 50. 7° d) 52. 7° 36. With a standard rectangular bar magnet of length (l), breadth (b; b << l) and magnetic momentM, the time period of the magnet in vibration magnetometer is 4 s. If the magnet is cut normal to its length into four equal pieces, the time period (in second) with one of the pieces a) 16 b) 2 c) 1 d) 1 4 37. A wire of length Lmetre carrying current i, ampere is bent in the form of a circle. What is the magnitude of magnetic of magnetic dipole moment? a) iL 2 /4π b) i 2 L 2 /4π c) i 2 L/8π d) iL 2 /8π 38. Two tangent galvanometer having coils of the same radius are connected in series. A current flowing in them produces of 60°and 45° 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 39. Two identical bar magnets with a length 10 cm and weight 50 g-weight are arranged freely with their poles facing in a inverted vertical glass tube. The upper magnet hangs in the air above the lower one so that Page| 4