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MULTIPLE CHOICE QUESTIONS, , wrest WITH ONE CORRECT ANSWER, , 5.1 THE BAR MAGNET, , 1. The length of a magnetized steel wire is, , , , (c) ¥2M,V3M; Zero ; Zero, (d) None of these, , / and its magnetic moment is M. It is 5. The distance between poles of horse shoe magnet, bent into the shape of L with two sides pole strength is 10 A m. The magnetic haa; « 8 10¢ and i, equal, The magnetic moment now will P midway between the poles is Nduction at @ Doing, pe (a) zero (b) 8x 10°T, @) > (b) 2M (c) 2x10°7T (d) 8x10" T, 2 6. A bar magnet is held perpendicular to a uniform fielg I, M couple acting on the magnet is to be halved by rotating ; : the, () ¥2M (d) v2 above position, the angle by which it is to be rotated js =, . The magnetic potential due to a magnetic dipole at a point on its (a) 30° (b) 60°, axis distant 40 cm from its centre is found to be 2-4 x 1079 J/A-m. (c) 40° (d) 90°, The magnetic moment of the dipole will be 7. Force between two identical short bar magnets whose centres, (a) 28-6 A-m? (b) 32:2 A-m? r metre apart is 8-1 N, when their axes are along the same ine., (c) 38-4 A-m2 (d) none of above separation is increased to 3 r and the axis are rearranged, . A magnetic needle is kept in a non-uniform magnetic field. It perpendicularly, the force between them would become, experiences (a) 24N (b) 1:2N, (a) aforce, but nota torque —_(b)_a force and a torque (c) O-IN (d) 0-05 N, (c) neither a force, nor a torque (d) a torque, but not a force 8. A magnetic needle suspended parallel to a magnetic field, (AIEEE 2005) requires a3 J of work to turn it through 60°. The torque needed to, _ What is the resultant magnetic moment of two magnets, each of maintain the needle in this position will be, ig gg :, magnetic moment M in Fig. 5.1.2 7 (a) 235 (b) 33, SAN, N 3, (a) (6) (c) WBJ (d) 53, 9. A bar magnet of magnetic moment 3-0 A-m? is placed in‘, uniform magnetic induction field of 2 x 10> T. If each pole of th, magnet experiences a force of 6 x 10~ N, the length of the, ‘ N S magnet is, S N S N (a) 05m (b) 0-3 m, () 02m (d) 0-1_m, e 10. A bar magnet of magnetic moment 2-0 Am? is free to rotate abou, a vertical axis through its centre. The magnet is released f°, rest from the east-west position. Find the kinetic energy se, magnet as it takes the north south position. The horizo# :, 60° component of the earth's magnetic field is B = 25 pT. Earth, S N magnetic field is from south to north., FIGURE 5.1.2 ee (b) 50 wJ, c, (d) 50J, . : : ; ‘ ; a, (a) V2M ; Zero; V3M ; Zero ah. 2 eingely magnetic needle is suspended from 1s ae, ‘ ‘ thread. Its upper end is now loaded with a mass of 50 ™, (6) V2M ; Zero ; Zero; 43M c with a m ais, . ~ : and the needle becomes horizontal. If the strength of ea EEE HO - te ROW aD, ' ; Et 6b 2d 8b 8d 100, , , , , , a, , Scanned with CamScanner

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Yr, 98-1 ab amp-cm and g = 98] cm/s?, of earth’s magnetic induction js, 0 gauss, (2) on - ” (6) 0-25 gauss, % Ss, (c) 0 = s ; (d) 0-05 gauss, magnets are sus a gi :, 12. Two mag pended by a given wire one by one. In order, , to deflect the first magnet through 45° 1 : j :, through 540° whereas with the second he wire has to be twisted, , —, , , , » then the vertical component, , (b) 372, , (d) 7/6, 13. Fig. 5.1.3 shows the various Positions, , (labelled by subscripts) of small 42, , magnetised needles P and Q. The oes, , arrows show the direction of their pv y, , magnetic moment. Which 4, , configuration corresponds to the es 0, fe ay Qs, , jowest potential energy among all the ‘ 7, , configurations shown ? Saape”, , (a) PQ; (b) PQ, To,, , (c) PQs (d) PQ, CS ey, 14. The ultimate individual unit of Magnetism in any magnet is, , called, , (a) North pole (b) South pole, , (c) Dipole (d) Quadrupole, , (MP PET 2002; J & K CET 2004), 15, How much work is done to rotate a magnet of dipole moment p,,,, in a magnetic field B through 180° ?, , B, (a) P,, 2 (b) p,, B, , (c) Pm = (d) 2p, B, , 16. A ber magnet of magnetic moment 3-0 A m? is placed in a uniform, magnetic induction field of 2 x 10~5 T. If each pole of the magnet, experiences a force of 6 x 10~+ N. The length of the magnet is, , (a) 0-5 m (b) 0-3 m, (c) 0-2 m (d)0-1m (EAMCET 2000), , 17. An iron rod of length L, and magnetic moments M is bent in the, form of a semicircle. Now the magnetic moment will be,, , (a) M (b) 2 Mix, , (c) Mix (d)Mx (Odisha JEE 2012), 18. A magnetic dipole is placed in a uniform magnetic field. The net, , Magnetic force on the dipole, , (a) Is always zero, , (b) depends on the orientation of the dipole, , (c) can never be zero, , (d) depends on the strength of the dipole (MP PET 2010), 19. A magnet of length 0-1 m and pole strength 10“ Am is kept in a, , Magnetic field of 30 Wb/m? at an angle of 30°. The couple acting, , On it is... x 10° N-m., , (a) 7-5 (b) 3-0, , fe) 1-5 (d) 60 (MP PET 2005), , %4. Points A und B are situated perpendicular to the axis of a 2 cm, long bar magnet at large distances x and 3 x from its centre on, , 16d 17.6, 27.6, , , , , , 21., , 22., , 23., , 25., , 27., , 18.4, , ; “I be, opposite sides. The ratio of the magnetic fields at A and B will, , approximately equal to, (a) 1:9 (b)2:9, , (¢)i27': 1 (d)9:1, , If a bar magnet of magnetic moment M is freely suspended ~ a, uniform magnetic field of strength B, work done in rotating the, magnet through an angle 8 is, (a) MB (1 — sin 8), , (c) MB cos 8, , (b) MB sin 8, (d) MB (1 — cos ®), , (Bihar CECE 2006), Two identical short bar magnets, each having magnetic moment, of 10 Am2, are arranged such that their 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 (Uy = 4 % x 10-7? Hm~'), , (b) V5 x 107? tesla, , (d) 45 x1073 tesla, (EAMCET 2005; Kerala PET 2011), , The magnetic induction in air at a distance d from an isolated, point pole of strength m unit will be, , (a) 42 x1077 tesla, (c) ¥2 x10-3 tesla, , m m, (a) = ), , (c) mS (d) md> (J & K CET 2005), A bar magnet of length 10 cm and having the pole strength equal, to 10-3 weber is kept in a magnetic field having magnetic, induction (B) equal to 4 x x 1073 tesla. It makes an angle of 30°, with the direction of magnetic induction. The value of the torque, acting on the magnet is ({ig = 4 m x 10~? weber/amp x m), (a)2xx107Nxm (b)2 xx 10°Nxm, (c)05Nxm (d) 0-5 x 107N xm, , (MP PET 2011), , 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) 3w (b) W, (c) By (d)2W (WB JEE 2012), , - Two identical thin bar magnets, each of length / and pole strength, , m units 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) 2 ml, , ], (c) J2 ml (d) qm! (MP PET 2002), , 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, , (MP PET 2005), , ANSWERS, , 19% ¢ Wc Ad = =622d, , urvarnS¢, Scanned with CamScanner

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28, ‘The magnetic potential at a point on the axial line of a bar magnet, of dipole moment M is V. What is the magnetic potential due to, bar magnet of magnetic moment. M/4 at the same point ?, , (a)4V (b)2V, (eo) VR (d) VIA, 29. A magnet of magnetic moment M is rotated through 360° in a, magnetic field H. The work done will be, (a) MH (6) 2 MH, (c) 2x MH (d) Zero (Roorkee 2000), , 30. A bar magnet of magnetic moment 200 A-m? is suspended in a, field of intensity 0-25 N/A-m. The couple required to, deflect it through 30° is, , (a) 50 N-m (6) 25 N-m, (c) 20 N-m (d) 15 N-m, (Pb. PET 2000; WB JEE 2013), , 31. Two similar bar magnets P and Q, each of magnetic moment M, are taken. If P is cut along the axial line and Q is cut along the, equatorial line all the four pieces obtained have, , (a) equal pole strength (6) magnetic moment M/4, (¢) magnetic moment M/2 (d) magnetic moment M, AND LAW, 1. SI unit of magnetic flux is, (a) tesla (b) tesla/m?, (c) tesla me? (d) none of the above, (NCERT Based), , 2. The dimensional formula of magnetic flux is, , () (ML? TA At} (b) (MLT* A}, , (c) IM L° TA} (d) (M°L' T? A}, , (NCERT Based), , 3. Isolated magnetic poles, called magnetic monopoles do not exist., , This is the conclusion of, , (a) Gauss’s theorem in electrostatics, , (6) Gauss's theorem in magnetism, , (c) Both (a) and (b) (d) Neither (a) nor (b), 4. Net magnetic flux through any closed surface is always, , (a) Negative (b) Positive ;, , (c) Zero (d) None of the above, , = a ew (NCERT Based), S. The magnetic lines of force inside a bar magnet, (¢) are from N-pole to S-pole of the magnet, (d) are from S pole to N-pole of the magnet (AIEEE 2003), & The magnetic Meld lines doe to a bar magnet ae conectly shown, 2 gE r : sh %, , fa) tm AF) tf, Ane, , (ce) (d), , Retna, I ire, 7. Magnetic lines of force a SePeehing 209, (a) always intersect, (b) are always closed curves,, (c) tend to crowd away from poles of magnet, (d) do not pass through vacuum, 8. The magnetic lines of force inside a bar magne;, (a) are from south pole to north pole of magnet, (b) are from north pole to south pole of magnet, (c) do not exist, (d) depend upon area of cross-section of bar magne;, 9, The incorrect statement regarding the lines of force of, magnetic field B is the, , (a) magnetic intensity is a measure of lines of fore,, through unit area held normal to it, , (b) magnetic lines of force form a close curve, , (c) inside a magnet, its magnetic lines of force move from, pole of a magnet towards its south pole North, , (d) due to a magnet, magnetic lines of force never cut each Other, 5.3 THE EARTH'S MAGNETISM, 1. A bar magnet 20 cm in length is placed with its south pole, , towards geographic north. The neutral points are situated y ,, distance of 40 cm from the centre of the magnet. If B,, = 3.2 ,, , 10~ Wb/m?, then the pole strength of the magnet is, (a) 9000 ab-amp x cm (b) 900. ab-amp x cm, (c) 225 ab-amp x cm (d) 450 ab-amp x cm, , 2. A dip circle is so set that its needle moves freely in the magnetic, meridian. In this position, the angle of dip is 40°. Now the dip, circle is rotated so that the plane in which the needle moves, makes an angle of 30° with the magnetic meridian. In this, position, the needle will dip by an angle, , a) 40° (b) 30°, (c) more than 40° (d) less than 40°, , 3. The angle of dip at a certain place is 30°. If the horizontal, component of the earth’s magnetic field is H, the intensity of the, total magnetic field is, , Passing, , H 2H, Oz » FF, © A @ wf, , (MP PMT 2002; MP PET 2000; Pb. PET 200°, 4. If a magnet is suspended at an angle of 30° to the magne®, , meridian, the dip needle makes an angle of 45° with, horizontal. The real dip is, , , , 7 =e, , , , ocanned WITN Lait 1Sc, , Scanned with CamScanner

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(b) 40°, (d) 60°, , imagnetic poles of the earth, a compass needle wil be, , (DCE 2003), , north (N)-pole, tance of 15 cm, , par magnet is 10 cm long, and is kept with its, ing north. A neutral point is formed at a dis, , m each pole. Given the horizontal Bamicsarne cs a, 0-4 Gauss, the pole strength of the inacnerse earth's field to, (b) 6-75 A-m, (d) 13-5 A-m, , ' (EAMCET 2009), long magnet is placed vertically with one pole on the table., , “point was found at 20 cm from the pole. What is the, if the horizontal component of earth’s field is 0-4 x, , 164 (b) 8 A-m, (o) Am (d) none, The angle of dip at a place is 40-6° and the intensity of the vertical, , component of the earth’s magnetic field V = 6 x 10° tesla. The, - total intensity of the earth’s magnetic field (J) at this place is, , , , , , , , , , , , Pe a, a 7 x 10° tesla (b) 6 x 10> tesla, (0) 5x 10° tesla (d) 92x 105 tesla, 74 S09. (Kerala PET 2009), , _ {6 The time of vibration of a dip needle vibrating in the vertical, pe’ the magnetic meridian is 3 seconds. When the same, etic needle is made to vibrate in the horizontal plane, the, : of vibration is 3/2 second, Then the angle of dip is, (b) 45°, (d) 90°, needle which is allowed to move in a horizontal plane, er iO geomagr oti pole. It, ill become rigid showing no movement, will ay in any position, il stay along N-S only, will stay along E-W only :, eneks of dip at two places are 30° and 45° respectively. The, ‘horizontal components of earth’s magnetic field at two, , , , , , , (b) 1:42, , (d) 1:2 (WB JEE 2013), , ———__—, , (d) 30°, , (AEMC 2000; WB JEE 2009; Kerala PET 2008), 14, The angle of dip at the magnetic equator is, , (a) 0° (b) 30° |, , (c) 45° (d) 90°, 15. The line on the earth’s surface joining the points where the field, , is horizontal is, , (a) magnetic meridian, , (c) magnetic line (d) magnetic equator, , (e) isogonic line (Pb. PET 2004), 16. The angle of dip at a certain place is 30°. If the horizontal, , component of the earth’s magnetic field is H, the intensity of the, total magnetic field is, , (c) 90°, , (b) magnetic axis, , H 2H, (a) a (b) 3, (c) H¥2 (@) HN3, , (UPSEAT 2000; MP PMT 2002; MP PET 2000; Pb. PET 2003), , 17. The angle of dip at a certain place on earth is 60° and the, magnitude of earth’s horizontal component of magnetic field is, 0:26 G. The magnetic field at the place on earth is, , (a) 0:13G (b) 0:26 G, (c) 0:52 G (d) 0-65 G, (AMU Engg. 2010 ; J & K CET 2010), 18. Which of the following relations is correct in magnetism ?, (a) R? = V+ H? (b)R=V+H, (c) V=R? + H? (d)V-=R+H, (Karnataka CET Engg. 2001), 19. Magnetic meridian is a, (a) point, (c) vertical plane, , (b) horizontal plane, (d) Line along N.S., , (Odisha JEE 2002), 20. The value of the horizontal component of the earth’s magnetic, , field and angle of dip are 1:8 x 10-5 weber/m? and 30°, , respectively at some place. The total intensity of earth’s magnetic, field at that place will be, , (a) 2:08 x 10-5 weber/m?, (b) 3-67 x 107 weber/m2, (c) 3-18 x 10-5 weber/m2, (d) 5-0 x 1075 weber/m2, , 21. A compass needle will show which of the following directions at, the earth’s magnetic pole ?, (a) vertical, (b) no particular direction, (c) Bent at 45° to the vertical, (d) horizontal, , 5.4 MAGNETIC INSTRUMENTS, , 1. The period of oscillation of a freely suspended bar magnet is 4, second. If it is cut into two equal parts in length, then the time, , (c) 0-5 sec _ d) 025 see ~— (AIMS 2010), , >cannea witn LamSc, Scanned with CamScanner

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2. Using a bar magnet P, a vibration magnetometer has time period 2, seconds, When a bar magnet Q (identical to P in mass and size) is, placed on top of P, the time period is unchanged. Which of the, followin: statements is true?, , (a) Q is of non-magnetic matenal, (6) @ is a bar magnet identical to P, and its north pole is placed, on top of P’s north pole, , (©) @ is of unmagnetised ferromagnetic material, (d) nothing can be said about properties of QO, , 3. In Tan A position, two short bar magnets of moments in the ratio, 1 : 1-7321 are placed at the same distance separately. If the, deflection produced for the first magnet is 30°, the deflection, produced for the second magnet will be, (a) 60° (b) 30°, , (c) 45° (d) 42°, , 4. The length, breadth and mass of two bar magnets are same but, their magnetic moments are 3 M and 2 M respectively. These are, joined pole to pole and are suspended by a string. When, oscillated in a magnetic field of strength B, the time period, obtained is 5 s. If the poles of either of the magnets are reversed,, then the time period of the combination in the same magnetic, field will be, , (a) 2V2s (b) 5V5s, , (c) Is (d) 373s, , 5. A vibration magnetometer consists of two identical bar magnets, placed one over the other such that they are perpendicular and, bisect each other. The time period of oscillation in a horizontal, magnetic field is 2 sec. One of the magnets is removed and if, the other magnet oscillates in the same field, then the time period, in seconds is :, , (a: 24 (b) 212, (c) 2 (d) 24 (EAMCET 2003), , 6. Two tangent galvanometers A and B have coils of radii 8 cm and, 16 cm respectively and resistance 8 Q each. They are connected, in parallel with a cell of emf 4 V and negligible internal, - resistance. The deflections produced in the tangent, , A and B are 30° and 60° respectively. If A has 2, * tums, then B must have, , {a) 1S tums (b) 12 turns, (c) 6 ums (d) 2 turns, (Karnataka CET 2007), , 7. A bar magnet used in a vibration magnetometer is heated so as to, reduce its magnetic moment by 19%. The periodic time of the, magnetometer will, (a) increase by 11% (b) decrease by 19%, , {c) increase by 19% (d) decrease by 11%, , 8. Two uniform magnetic fields B and H are perpendicular to each, other at a place. When a magnetic needle is placed in the field, it, rests making angle 60° and 30° with B and H respectively. The, , value of B : H is, (a) 1:2 (6) 2:1, enti: 0 Pein (@) 1:43 (MP PET 2007), 9. The period of oscillation of a magnet in vibration magnetometer, , is 2 sec. The period of oscillation of a magnet whose magnetic, moment is four times that of the first magnet is, , , , (a) 1 sec (b) 4 sec SS, (c) 8 sec (d) 0-5 sec y ql, 10. Two magnets are held together in a Vibratio OP, are allowed to oscillate in the earth’s ma ; MaBNeton, 240,, poles together. 12 oscillations per minut weOc ss d ~, , leld ,,., . © are Ww and, poles together, only 4 oscillations made by fort, ratio of their magnetic moments is, , ij, Per Minute are cree, (a) 3:1 (6) 133, (ec) 3:5 (dq) 5:4 i, 11. A certain amount of current when flowing jn UMrry, , tangent galvanometer produces a deflection of 4s a Properly :, Sey, , ie: If, be reduced by a factor of ¥3, the deflection would n, , (a) decrease by 30° (6) increase by 3¢p, (c) increase by 15° (d) decrease by 150, 12. The magnetic needle of an oscillation magnetomet, oscillations per minute under the action of earth's er, alone. When a bar magnet is placed at some dist, axis of the needle, it makes 14 oscillations per mi, , magnet is turned so that its poles interchange thei, the new frequency of oscillation of the needle is, , (a) 10 vibrations per minute, (c) 4 vibrations per minute, 13. For protecting a sensitive equipment from the externa] ma, field, it should be, (a) placed inside an aluminium case, (b) placed inside an iron case, (c) wriapped with insulation, (d) surrounded with fine copper sheet., 14. A tangent galvanometer is connected directly to an ideal battery, If the number of turns in the coil is doubled, the deflection yili, (a) increase (b) decrease, (c) remain unchanged (d) either increase or decrease, (MP PET 2010), , 15. At a certain place, a magnet makes 30 oscillations per minute. At, another place where the magnetic field is double, its time period, will be, , (a) 4 sec (b) 2 sec, , (c) 1/2 sec (d) V2 sec (Kerala PET 2012), , 16, Two uniform magnetic fields B and H are perpendicular to each, other at a place. When a magnetic needle is placed in the field, it, rests making angles 60° and 30° with B and H respectively. The, value of B : H is, , (a) 1:2 (b) 2:1, , (c) ¥3:1 (d) 1:¥3.— (MP PET 2007), , 17. The radius of the coil of a Tangent galvanometer which yd, turns is 0-1 m. The current required to produce a deflection of, (By =4 x 10° T) is, (a)3A (b) 1-1 A is, (c)2-1A (d) 1-5A (MP PET, , ‘ 9, , 18. A magnet oscillating in a horizontal plane has a time period, second at a place where the angle of dip is 30° and 3 $y, , 0, , another place where the angle of dip is 60°. The rati, magnetic fields at the two places is, , CUtren,, , m makes, ®gnetic fj, , el, , ance along =, , NUte. If the :, , * Position, then, , 19, , (6) 14 vibrations Per Minute, (d) 2 vibrations per Minute, , ENetic, , aga 14, , >cannea woth,, , Scanned with CamScanner