Magnetism Exercise

Corporate Office: CP Tower, Road No.1, IPIA, Kota (Raj.), Ph: 0744-2434159 MAGNETISM 114

Total number of Questions in this chapter are :

(i) Level # 1 ....................... 68

(ii) Level # 2 ....................... 62

(iii) Level # 3 ....................... 26

(iv) Level # 4 ....................... 09

Total no. of questions ....................... 165

Preface

As you have gone through the theory part that consists of given fundamental principles, definitions,

concepts involved and solved problems. After going through theory part it becomes necessary to

solve the unsolved problems based on the concepts given. To solve this purpose we are providing

exercise part that comprises of various exercises based on the theory. By solving various kinds of

problems you can check your grasp on the topic and can determine whether you have been able to

find optimum depth in relevant topic or not.

Students are advised to solve the questions of exercises (Levels # 1, 2, 3, 4) in the same sequence

or as directed by the faculty members, religiously and very carefully.

Level # 3 is not for foundation course students, it will be discussed in fresher or target courses.

The list of exercises is as following :

MAGNETISM


LEVEL # 1Questionsbased on Bar magnet

Q.1 The ratio of magnetic fields due to a smallerbar magnet in the end on position to broadside on position is-(A) 1/4 (B) 1/2(C) 1 (D) 2

Q.2 Potential energy of a bar magnet of magneticmoment M placed in a magnetic field ofinduction B such that it makes an angle with the direction of B is -(A) MB sin (B) – MB cos (C) MB (1 - cos (D) MB (1+ cos

Q.3 In the above question, torque acting onmagnet is -(A) MB sin (B) – MB cos (C) MB cos (D) MB (1 - cos )

Q.4 In Q.No. 3 position of stable equilibrium ofmagnet is given by equal to -(A) 0º (B) 90º(C) 45º (D) 180º

Q.5 A current of 3 A is flowing in a plane circularcoil of radius 4 cm and number of turns 20.The coil is placed in a uniform magnetic fieldof magnetic induction 0.5 T. Then the dipolemoment of the coil is -(A) 3000 Am2 (B) 0.3 Am2

(C) 300 A m2 (D) 75 A m2

Q.6 A current carrying loop is placed in a uniformmagnetic field. The torque acting on it doesnot depend upon -(A) area of loop (B) shape of loop(C) value of current (D) magnetic field

Q.7 The points A and B are situated perpendicularto the axis of 2 cm long bar magnet at largedistances x and 3 x from the centre onopposite sides. The ratio of magnetic fieldsat A and B will be approximately equal to -(A) 27 : 1 (B) 1 : 27(C) 9 : 1 (D) 1 : 9

Q.8 A compass needle is placed at the magneticpole it -(A) points N–S(B) points EW(C) becomes vertical(D) may staying any direction

Q.9 A bar magnet is cut into two equal halved bya plane parallel to the magnetic axis. Of thefollowing physical quantities the one whichremains unchanged is -(A) pole strength(B) magnetic moment(C) Intensity of manetisation(D) Moment of inertia

Q.10 Two isolated point poles of strength 30 A.mand 60 A-m are placed at a distance of0.3 m. The force of repulsion S.(A) 2 × 10-3 N (B) 2 × 10-4 N(C) 2 × 105 N (D) 2 × 10-5 N

Q.11 Magnetic lines of force are -(A) continuous(B) discontinuous(C) sometimes continuous and sometimes

discontinuous(D) nothing can be said

Q.12 Units of pole strength of a magnet are -(A) A m-1 (B) A m2

(C) A m-2 (D) A m

Q.13 Magnetic monopoles cannot exist -(A) true(B) false(C) may be true or false(D) nothing can be said

Q.14 A tiny loop of current behaves as a magneticdipole -(A) true(B) false(C) may be true or false(D) nothing can be said

Q.15 Magnetic field intensity due to a dipole variesas dn, where n =(A) 2 (B) –2(C) 3 (D) – 3


Q.24 Calculate force exerted on a point N pole of3200 A-m placed 10 cm away from a pointsouth pole of 10 A-m in air.(A) 1 N (B) 0.32 N(C) 2 N (D) 3 N

Q.25 Force acting on a magnetic pole of 7.5×10–2

A-m is 1.5 N. Magnetic field at the point is-(A) 20 Wb/m2 (B) 50 Wb/m2

(C) 112.5 T (D) 2.0 T

Q.26 Magnetic potential at a point distant d froma magnetic pole of strength m is -

(A) 4

0 dm

(B) 20

dm

4

(C) dm2

40

(D) None of these

Q.27 Force between two magnetic poles dependson -(A) pole strength only(B) distance only(C) medium only(D) All the three above

Q.28 A point at which two or more magnetic fieldscancel each other is called.(A) focal point (B) inversion point(C) neutral point (D) none of these

Questionsbased on Earth magnet

Q.29 The horizontal component of earth’s magneticfield at any place is 0.36 × 10-4 Weber/m2.If the angle of dip at that place is 60º thenthe value of vertical component of earth’smagnetic field will be (in Wb/m2)(A) 0.12 × 104 (B) 0.24 × 104

(C) 0.40 × 104 (D) 0.62 × 104

Q.30 The value of angle of dip at a place on earthis 45º. If the horizontal component of earth’smagnetic field is 5 x 105 Tesla then thetotal magnetic of earth’s magnetic field ofearth will be

(A) 5 2 × 105 Tesla

(B) 10 2 × 105 Tesla

(C) 15 2 × 105 Tesla

(D) zero

Q.16 A short bar magnet place with its axis at30º, with a uniform external magnetic field of0.25 T experiences a torque of 4.5×10-2 N-mMagnetic moment of the magnet is -(A) 0.36 JT–1 (B) 0.72 JT–1

(C) 0.18 JT–1 (D) zero.

Q.17 A closely wound solenoid of 800 turns hasarea of cross section 2.5 cm2. Magneticmoment associated with it, when it carries acurrent of 3 A is -(A) 0.6 JT–1 (B) 0.06 JT–1

(C) 6 JT–1 (D) None of these

Q.18 The magnetic field strength at distance d dueto an isolated pole of strength m ampere is-

(A) 4

0 dm

(B) 4

0 3dm

(C) 4

0 )td(m

22 (D) 4

0 m/d2 .

Q.19 The magnetic field due to a magnetic dipoleof magnetic moment M at a point on the axisof the dipole and at a distance d from it(in cgs Unit) is given by -(A) M/d2 (B) 2M/d2

(C) 2M/d3 (D) 2M/d4

Q.20 The magnetic moment of a magnet is0.1 amp × m2 . It is suspended in a magneticfield of intensity 3 × 10-4 weber/m2. Thecouple acting upon it when deflected by 30ºfrom the magnetic field is -(A) 1 × 10–5 Nm (B) 1.5 × 10–5 Nm(C) 2 × 10–5 Nm (D) 2.5 × 10–5 Nm

Q.21 In the unmagnetized state, magnetic domainsof a magnetic substance are oriented at -(A) 60º (B) 90º(C) Randomly (D) zero

Q.22 The time period of a freely suspended magnetdoes not depend upon -(A) length of magnet(B) pole strength of magnet(C) horizontal component of earth’s field(D) length of the suspension

Q.23 The magnetic induction B and the force F ona pole m are related by -

(A) B = mF (B) F = mB

(C) F = mB (D) None of these


Q.31 At a certain place, horizontal component is

3 times the vertical component. The angle

of dip of this place is -(A) 0 (B) /3(C) /6 (D) none of these

Q.32 When a magnet marked N S is suspended ina horizontal position, so that it is free torotate, the pole marked N shall point towards-(A) south pole of earth’s magnet(B) north pole of earth’s magnet(C) geographic N pole(D) geographic S pole.

Q.33 Two bar magnets of the same mass, samelength and breadth but having magneticmoments M and 2 M are joined together polefor pole and suspended by a string. The timeperiod of assembly in a magnetic field ofstrength H is 3 seconds. If now the polarityof one of the magnets is reversed andcombination is again made to oscillate in thesame field, the time of oscillating is -

(A) 3 sec (B) 3 3 sec(C) 3 sec (D) 6 sec

Q.34 The periods of oscillation of two magnets inthe same field are in the ratio 2 : 1. If theirmoments of inertia are equal, ratio of theirmagnetic moments is -(A) 1 : 2 (B) 1 : 4(C) 2 : 1 (D) 4 : 1

Q.35 Time periods of vibration of two bar magnetsin sum and difference positions are 4 secand 6 sec respectively. The ratio of their

magnetic moments 2

1

MM

is -

(A) 6 : 4 (B) 30 : 16(C) 2.6 :1 (D) 1.5 : 1

Questionsbased on Instruments

Q.36 Two magnets A and B are equal in length,breadth and mass, but their magneticmoments are different. If the time period of Bin a vibration magnetometer is twice that ofA, then the ratio of magnetic moments willbe(A) 1/2 (B) 2(C) 4 (D) 12

Q.37 The time period of vibration of two magnetsin sum position is 3 sec. When polarity ofweaker magnet is reversed, the combinationmakes 12 oscillations per minute. Comparethe magnetic moments of two magnets.

(A) 4 (B) 817

(C) 813

(D) 41

Q.38 The period of oscillation of a bar magnet ina vibration magnetometer is 2 Sec. The periodof oscillation of a bar magnet whose magneticmoment is 4 times that of 1st magnet is -(A) 4sec (B) 1 sec(C) 2 sec (D) 0.5 sec

Q.39 The time period of oscillation of a magnet ina vibration magnetometer is 1.5 sec. The timeperiod of oscillation of another magnet similarin size, shape and mass but having 1/4magnetic moment than that of the 1st magnetoscillating at the same place will be –(A) 0.75 sec (B) 1.5 sec(C) 3.0 sec (D) 6.0 sec

Q.40 The period of oscillation of a magnet in avibration magnetometer is 2 seconds. Theperiod of oscillate of a magnet of moment ofinertia four times that of the first magnet is-(A) 1 sec (B) 4 sec(C) 8sec (D) 0.5 sec

Q.41 The arms of a deflection magnetometer inthe tangent B position are placed along(A) the east west direction(B) the north south direction(C) the north east-south west direction(D) the north west-south east direction .

Q.42 The arms of a deflection magnetometer inthe tangent B position are placed along(A) The east - west direction(B) The north - south direction(C) The north east, south west direction(D) The north west, south east direction.

Q.43 The direction of magnet in Tan B position isalong.(A) North south (B) East west(C) North west (D) South west


Questionsbased on Magnetic properties of material

Q.44 The correct curve between X and T1

for

paramagnetic magnetic is

(A) (B)

(C) (D)

Q.45 The volume susceptibility of a magneticmaterial is 30 x 104. Its relative permeabilitywill be -(A) 31 × 104 (B) 1.003(C) 1.0003 (D) 29 × 104

Q.46 A rod of ferromagnetic material withdimensions 10 cm x 0.5 cm × 0.2 cm isplaced in a magnetic field of strength0.5×104 amp/m as a result of which amagnetic moment of 5 amp-m2 is producedin the rod. The value of magnetic inductionwill be(A) 0.54 Tesla (B) 0.358 Tesla(C) 2.519 Tesla (D) 6.28 Tesla

Q.47 On placing a piece of ferromagnetic materialof cross-sectional area 1cm2 in magnetic fieldof 200 oersted, flux density of 3000 Gauss isproduced in it. The values of relativepermeability and magnetic susceptibility ofthe material will respectively be -(A) 11.9 and 150 (B) 150 and 11.9(C) 50 and 11.9 (D) 15 and 14

Q.48 The mass of an iron rod is 80 gm and itsmagnetic moment is 10 A-m2. If the densityof iron is 8 gm/C.C. then the value of intensityof magnetisation will be(A) 106 A/m (B) 104 A/m(C) 102 A/m (D) 10 A/m

Q.49 If µ0 is absolute permeability of vacuum andµr is relative magnetic permeability of anothermedium, then permeability µ of the mediumis -(A) µ0 µr (B) µ0/µr(C) µr/µ0 (D) 1/µ0µr

Q.50 Every atom of every substance is a completemagnet in itself.(A) true(B) false(C) may be true or fals(D) nothing can be said

Q.51 The dimensions of magnetic permeability are-(A) [MLT–2 A–2] (B) [ML2 T–2 A–2](C) [ML2 T–2 A–1] (D) [M–1LT–2 A–2]

Q.52 S.I. unit of magnetic permeability is -(A) A-m (B) Am2

(C) H-m (D) H/m

Q.53 For a diamagnetic material(A) µr > 1 m > 1 (B) µr > 1 m < 1(C) µr < 1 m < 0 (D) µr < 1 m > 0

Q.54 The most suitable metal for making electromagnets and transformer cores is -(A) steel (B) iron(C) copper (D) aluminium

Q.55 The most suitable metal for permanentmagnets is -(A) steel (B) iron(C) copper (D) aluminium

Q.56 Curie’s law states that(A) magnetic susceptibility is inversely

proportional to the absolute temperature(B) magnetic susceptibility is inversely

proportional the square root of the absolutetemperature

(C) magnetic susceptibi l i ty is directlyproportional to the absolute temperature

(D) magnetic susceptibility

Q.57 For a paramagnetic material, the dependenceof the magnetic susceptibility , on theabsolute temperature T is given by -(A) T(B) = constant T

(C) T1

(D) = constant.


Q.58 Domain formation is a necessary feature of -(A) diamagnetism (B) ferromagnetism(C) paramagnetism (D) all of the above.

Q.59 The permanent magnetic moment of atomsor molecules of a diamagnetic material is -

(A) small (B) large(C) negative (D) zero.

Q.60 The relation between magnetic susceptibilityxm and relative permeability µr, is -(A) xm = µr (B) xm – 1 = µr(C) µr = 1 + xm (D) µr = 1 – xm

Q.61 When a ferromagnetic material is heatedabove its Curie temperature,(A) it gets demagnetised(B) it becomes diamagnetic(C) behaves like a paramagnetic substance(D) remains unaffected

Q.62 If M is magnetic moment developed in thematerial having volume V, then intensity ofmagnetisation is given by the expression(A) MV (B) M/V(C) M V (D) M/ V

Q.63 The relative permeability of a medium is0.075. What is its magnetic susceptibility ?(A) 0.925 (B) - 0.925(C) 1.075 (D) - 1.075

Q.64 The moment of a magnet (15 cm × 2 cm ×1 cm) is 1.2 A-m2. What is its intensity ofmagnetisation ?(A) 4 × 104 Am-1 (B) 2 × 104 Am-1

(C) 104 Am-1 (D) None

Q.65 The hysterisis curve is studied generally for-(A) ferromagnetic materials(B) paramagnetic materials(C) diamagnetic materials(D) all of these

Q.66 In normal iron piece,(A) there are no magnetic dipoles(B) magnetic dipoles are arranged in a

paticular direction(C) magnetic dipoles are oriented randomly(D) none of the above.

Q.67 As magnetising field on a ferromagneticmaterial is increased, its permeability -(A) increases (B) decreass(C) remains constant (D) cannot say.

Q.68 The hysteresis cycle for the material ofpermanent magnet is -(A) Short and wide (B) all and narrow(C) Tall and wide (D) Short and narrow


LEVEL # 2Q.1 A magnet is broken into three pieces in

length. The strength of the new poles is thestrength of the poles of original magnet.(A) the same as (B) one half(C) double (D) one third

Q.2 Magnetic field produced by electrons in aotmsand molecules is due to their -(A) spin motion only(B) orbital motion only(C) spin and orbital motion both(D) neither spin nor orbital motion.

Q.3 A steel wire of length has a magneticmoment M. It is then bent into a semicirculararc. The new mangetic moment is -(A) M (B) 2 M/(C) M/ (D) M

Q.4 Two identical thin bar magnets each of length and pole strength m are placed at rightangles to each other, with north pole of onetouching south pole of the other, then themagnetic momenta of the system is -(A) 1 m (B) 2 m

(C) 2 m (D) m/2.

Q.5 A sensitive magnetic instrument can beshielded very effectively from outside magneticfields by placing it inside a box of -(A) wood(B) plastic(C) metal of high conductivity(D) soft iron of high permeability

Q.6 The ratio of magnetic potentials due tomagnetic dipole in the end on position tothat in broadside on position for the samedistance from it is -(A) zero (B) (C) 1 (D) 2

Q.7 The magnetic potential at a point distant10 cm from the middle point of a magneticdipole on a line incline at an angle of 60ºwith the axis is 3 e.m.u. Then the magneticmoment of magnet is -

(A) 600 ab - amp cm2

(B) 300 ab - amp cm2

(C) 150 ab - amp cm2

(D) 300 3 ab - amp cm2

Q.8 A thin bar magnet of length 2 and breadth2b pole strength p and magnetic mometn Mis divided into four equal pars with length andbreadth of each part being half of originalmagnet. Then the pole strength of each partis-(A) p (B) p/2(C) 2p (D) p/4

Q.9 In the above question, manetic moment ofeach part is -(A) M/4 (B) M(C) M/2 (D) 2M

Q.10 When a magnet is heated, its strength –(A) always decreases(B) always increases(C) may increase or decrease(D) remains unaffected

Q.11 A magnetic needle is kept in a non–uniformmagnetic 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 force nor a torque

Q.12 Two points A and B are situated at a distancex and 2 x respectively from the nearer poleof a magnet 2 cm long. The ratio of magneticfield at A and B is –(A) 4 : 1 exactly(B) 4 : 1 approximately(C) 8 : 1 approximately(D) 1 : 1 approximately

Q.13 The magnet of pole strength m and magneticmoment M is cut into two pieces along itsaxis. Its pole strength and magnetic momentnow becomes –

(A) 2m

, 2M

(B) m, 2M

(C) 2m

, M (D) m, M


Q.14 The distance between two magnetic poles isdoubled and their pole strength is alsodoubled. Force between them –(A) remains unchanged(B) becomes twice(C) becomes 8 times(D) becomes 4 times

Q.15 A large magnet is broken into two pieces sothat their lengths are in the ratio 2 : 1. Thepole strengths of the two pieces will haveratio –(A) 2 : 1 (B) 1 : 2(C) 4 : 1 (D) 1 : 1

Q.16 A circular coil of radius 4 cm having 50 turnscarries a current of 2A. It is placed in uniformmagnetic field of intensity of 0.1 weber/m2.The work done to rotate the coil from theequilibrium position by 180° is –(A) 0.1 J (B) 0.2 J(C) 0.4 J (D) 0.8 J

Q.17 A circular coil of radius 4 cm having 20 turnscarries a current of 3 A. It is placed in amagnetic field of intesity 0.5 weber/m2. Thepotential energy of the magnetic dipole of thecoil is –(A) – 0.15 J (B) – 0.3 J(C) – 0.45 J (D) – 0.6 J

Q.18 A magnetic dipole is placed at right anglesto the direction of lines of force of magneticinduction B. If it is rotated through an angleof 180°, then the work done is –(A) MB (B) 2 MB(C) – 2 MB (D) Zero

Q.19 A magnetic field exerts no force on–(A) a magnet(B) an unmagnetised iron bar(C) a moving charge(D) a charge at rest

Q.20 The line joining a point to the centre of ashort magnet makes angles with the axis.Potential at a point distant d from the centreof magnet, on this line is –

(A) 20

d4sinMµ

(B) 2

0

d4cosMµ

(C) 30

d4Mµ

(D) none of these

Q.21 Potential at any point on equatorial line ofdipole is –(A) µ0 M/4 d2 (B) µ0 M/4 d3

(C) zero (D) none of these

Q.22 The value of angle of dip is zero at themagnetic equator because on it –(A) V and H are equal(B) the value of V and H is zero(C) the value of V is zero(D) the value of H is zero

Q.23 The error in measuring the current with atangent galvanometer is minimum when thedeflection is about –(A) 0° (B) 30°(C) 45° (D) 60°

Q.24 The needle of a dip circle when placed at ageomagnetic pole stays along –(A) South north direction only(B) East west direction only(C) Vertical direction(D) None of the above

Q.25 Earth’s magnetic field always has a horizontalcomponent except at –(A) equator(B) magnetic pole(C) a latitude of 60°(D) an inclination of 60°

Q.26 The lines of force due to earth’s horizontalmagnetic field are –(A) parallel and straight(B) concentric circle(C) elliptical(D) curved lines

Q.27 The vertical component of earth’s magneticfield is zero at –(A) magnetic equator (B) magnetic pole(C) geographic poles (D) at 90° latitude

Q.28 A dip needle which is free to move in a verticalplane perpendicular to magnetic meridian willremain –(A) horizontal(B) vertical(C) neither horizontal nor vertical(D) nothing can be said


Q.29 The angles of dip at the poles and the equatorrespectively are –(A) 30°, 60° (B) 90°, 0°(C) 30°, 90° (D) 0°, 0°

Q.30 The angle of dip at a certain place where thehorizontal and vertical components of theearth’s magnetic field are equal is –(A) 30° (B) 75°(C) 60° (D) 45°

Q.31 If a magnet is suspended at angle 30° to themagnetic meridian, the dip needle makes anangle of 45° with the horizontal. The real dipis –

(A) tan–1 ( 2/3 ) (B) tan–1 ( 3 )

(C) tan–1 ( 3 /2) (D) tan–1 (2/ 3 )

Q.32 A magnetic dipole is placed in two

perpendicular magnetic fields B

and H

and

is in equilibrium making angle with B

. Then(A) B = H(B) B cos = H sin (C) B sin = H cos (D) B = H tan

Q.33 When a magnet is suspended horizontally atneutral point, its frequency of oscillation is –(A) zero(B) infinity(C) neither of the two(D) nothing can be said

Q.34 A deflection magnetometer can be used formeasuring –(A) declination(B) dip(C) horizontal component(D) all these

Q.35 Lines passing through points of zerodeclination are –(A) isogonic lines (B) isoclinic lines(C) agonic lines (D) aclinic lines

Q.36 A mariner’s compass shows –(A) geographic NS direction(B) magnetic NS direction(C) both of (A) and (B)(D) none of these

Q.37 A hydrogen atom is a paramagnetic. Ahydrogen molecule is –(A) Diamagnetic (B) Paramagnetic(C) Ferromagnetic (D) None of these

Q.38 The magnetic moment of atomic neon isequal to –

(A) zero (B) 21

µB

(C) 23

µB (D) 2 µB

Q.39 The core of an electromagnet is made of softiron, because –(A) the susceptibility of soft iron is very high(B) coercivity of soft iron is very low(C) both of these(D) none of these

Q.40 A permanent magnet –(A) attracts all substances(B) attracts only ferromagnetic substances(C) attacts ferromagnetic substances and

repels all others(D) attracts some substances and repels

others

Q.41 Ferromagnetics owe their properties to –(A) filled inner subshells(B) vacant inner subshells(C) partially filled inner subshells(D) all the subshells equally filled

Q.42 The relative permeability of a substance X isslightly less than unity and that of substanceY is slightly more than unity then –(A) X is paramagnetic and Y is ferromagnetic(B) X is diamagnetic and Y is ferromagnetic(C) X and Y both are paramagnetic(D) X is diamagnetic and Y is paramagnetic


Q.43 Hysterisis is the phenomenon of lagging of –(A) behind B (B) B behind (C) and B behind H (D) H behind

Q.44 The magnetising field required to be appliedin opposite direction to reduce residualmagnetism is zero is called –(A) coercivity (B) retentivity(C) hysterisis (D) none of these

Q.45 When magnetising field on a bar of steel isincreased, its magnetisation –(A) goes on decreasing(B) goes on increasing(C) goes on increasing first and then

decreases(D) goes on increasing till it becomes

constant

Q.46 If relative permeability of iron is 2000. itsabsolute permeability in S.. units is –(A) 8 × 10–4 (B) 8 × 10–3

(C) 800/ (D) 5 × 109/

Q.47 Maximum magnetisation of a paramagneticand ferromagnetic sample is –(A) of the same order(B) smaller for para and larger for ferro(C) smaller can be predicted(D) nothing can be predicted

Q.48 A dip needle in a plane perpendicular tomagnetic meridian will remain –(A) vertical(B) horizontal(C) In any direction(D) At an angle of dip to the horizontal

Q.49 A dip needle arranged to move freely in themagnetic meridian dips by an angle 0. If thevertical plane in which the needle moves isrotated through an angle to the magneticmeridian, then the needle will dip by an angle(A) (B) (C) More than (D) Less than

Q.50 Of dia, para and ferromagnetism, the universalproperty of all substances is –(A) Diamagnetism (B) Paramagnetism(C) Ferromagnetism (D) All the above

Q.51 The magnetic field due to a short magnet ata point in Tan A position at a distance x cmfrom the middle point of the magnet is 200gauss. The magnetic field at a point in TanB position at a distance x cm from the middleof the magnet is –(A) 100 gauss (B) 400 gauss(C) 50 gauss (D) 200 gauss

Q.52 A uniform magnetic field parallel to the planeof paper, existed in space initially directedfrom left to right. When a bar of soft iron isplaced in the field parallel to it, the lines offorce passing through it will be representedby Fig.

(A)

(B)

(C)

(D)

(A) A (B) B(C) C (D) D

Q.53 A magnet is placed on a paper in a horizontalplane for locating neutral points. A dip needleplaced at the neutral point will be horizontalat the –(A) Magnetic poles(B) Magnetic equator(C) Latitude angle 45°(D) Latitude angle of 60°


Q.54 A bar magnet 8 cms long is placed in themagnet i c m eri di an wi th the N–polepointing towards geographical north. Twoneutral points separated by a distance of6 cms are obtained on the equatorial axisof the magnet. If horizontal component ofearth’s field = 3.2 × 10–5 T, then pole strengthof magnet is –(A) 5 ab-amp × cm(B) 10 ab-amp × cm(C) 2.5 ab-amp × cm(D) 20 ab-amp × cm

Q.55 The variation of magnetic susceptibility (x)with absolute temperature T for a diamagneticmaterial is given by –

(A)

(B)

(C)

(D)

Q.56 A bar magnet 20 cms in length is placedwith its south pole towards geographicalnorth. The neutral points are situated ata distance of 40 cms from centre of themagent. If horizontal component of earth’sfield – 3.2 × 10–5 weber/metre2 then polestrength of magnet is –(A) 9000 ab-amp × cm(B) 90 ab-amp × cm(C) 450 ab-amp × cm(D) 225 ab-amp × cm

Q.57 A dip needle lies initially in the magneticmeridian when it shows an angle of dip ata place. The dip circle is rotated through anangle x in the horizontal plane and then it

shows an angle of dip . Then

tantan

is –

(A) xcos1

(B) xsin1

(C) xtan1

(D) cos x

Q.58 The time of vibration of a dip needle vibratingin the vertical plane in the magnetic meridianis 3 seconds. When the same magneticneedle is made to vibrate in the horizontalplane, the time of vibration is 3 2 second.Then the angle of dip is –(A) 30° (B) 45°(C) 60° (D) 90°

Q.59 Two short magnets have equal pole strengthsbut one is twice as long as the other. Theshorter magnet is placed 20 cms in tan Aposition from the compass needle. The longermagnet must be placed on the other side ofthe magnetometer for no deflection at adistance equal to –(A) 20 cms (B) 20 (2)1/3 cms(C) 20 (2)2/3 cms (D) 20 (2)3/3 cms

Q.60 A dip needle vibrates in the vertical planeperpendicular to the magnetic meridian. Thetime period of vibration is found to be2 seconds. The same needle is then allowedto vibrate in the horizontal plane, and thetime period is again found to be 2 seconds.Then the angle of dip is –(A) 0° (B) 30°(C) 45° (D) 90°


Q.61 Two identical thin bar magnets each of lengthl and pole strength m are placed at rightangles to each other with north pole of onetouching the south pole of other, magneticmoment of the system is -(A) 1 ml (B) 2 ml

(C) 2 ml (D) 21

ml

Q.62 A steel wire of length l has a magneticmoment M. It is bent into L-shape as shownin fig. The new magnetic moment is-

/2

/2

(A) M (B) M/ 2(C) M/2 (D) 2M


LEVEL # 3Q.1 A wire of length L metre carrying a current

i ampere is bent into a square. Themagnitude of its magnetic moment will be :

(A) 4

iL2(B)

4iL2

(C) 8

iL2(D)

16iL2

Q.2 Two identical magnetic dipoles of magneticmoment 1.0 A-m2 each, placed at aseparation of 2m with their axis perpendicularto each other. The resultant magnetic field ata point midway between dipoles is

(A) T105 7 (B) T103 7

(C) T102 7 (D) zero

Q.3 Two short barmagnet of magnetic momentsM1 and M2 are kept on X and Y axis asshown is figure. If resultant magnetic field at

origin is zero, Then 2

1MM

will be

2d

d

N

M2

S OM1

NS

(A) 1 : 4 (B) 4 : 1(C) 2 : 1 (D) 8 : 1

Q.4 A magnet of length 14 cm and magneticmoment is broken into two parts of length 6cm and 8 cm. They are put at right angles toeach other with opposite poles together. Themagnetic dipole moment of the combination is-

(A) 4.1

(B)

(C) 1.4 (D) 2.8

Q.5 If 1 ,2 ,3 and 4 are the magnetic torque

acting on the bar magnet when it kept at an

angles of 30°, 60°, 90° and 135° with the

direction of magnatic field. Then-

(A) 1 > 2 > 3 > 4

(B) 3 > 1 > 2 > 4

(C) 4 > 3 > 2 > 1

(D) 3 > 2 > 4 > 1

Q.6 The potential energy of a bar magnet havingmagnetic moment M in kept in uniformmagnetic field B as shown is

N

S60° B

(A) 2MB

(B) 2

MB

(C) MB (D) –MB

Q.7 Torques 1 and 2 are required for a magneticneedle to remain perpendicular to themagnetic fields at two different places. Themagnetic field at those places are B1 and B2

respectively, then 2

1BB

is

(A) 2

1

(B) 1

2

(C) 21

21

(D) 21

21

Q.8 In a diflection magneto meter experiment thedeflections produced seprately by two shortbar magnets kept at same distance are 45°and 30°. Then the ratio of the magnaticmoments of the two magnets is :

(A) 2:3 (B) 1:3

(C) 1:2 (D) 3:1

2M

S

S NN


Q.9 A rod of a paramagnetic substance is placed ina non-uniform magnetic field. Which of thefollowing figure shows its alighnment in thefield?

(A) N S

(B) N S

(C) N S

(D) N S

Q.10 The work done in turning a magnet of magneticmoment M by an angle of 90° from themeridian is n times the corresponding workdone to turn it through an angle of 60°. Then-

(A) 21n (B) n = 2

(C) 41n (D) n = 1

Q.11 A magnetic needle vibrates in a vertical planeparallel to the magnetic meridian about ahorizontal axis passing through its centre. Itsfrequency is n. If the plane of oscillation isturned about a vertical axis by 90°, thefrequency of its oscillation in vertical plane willbe-(A) n (B) zero(C) less then n (D) more then n

Q.12 A magnetised wire of moment M is bentinto an arc of a circle subtending an angle of

60° at the centre; then the new magneticmoment is –(A) (2M/) (B) (M/)

(C) )/M33( (D) (3M/)

Q.13 Find the angle through which a magnet is tobe rotated from rest position when it issuspended in a magnetic field so that itexperiences half of the maximum couple:(A) 60° (B) 30°(C) 45° (D) 90°

Q.14 A magnet is parallel to a uniform magnetic field.If it is rotated by 60°, the work done is 0.8 J.How much work is done in moving it 30° further?(A) 0.8 × 107 ergs (B) 0.4 J(C) 8 J (D) 0.8 ergs

Q.15 A magnetic needle lying paral lel to amagnetic field required W units of work toturn it through 60°. The torque required tomaintain the needle in this position will be :

(A) W3 (B) W

(C) 2/W3 (D) 2W

Q.16 The magnet of a vibration magnetometer isheated so as to reduce its magneticmoment by 19%. By doing this the periodictime of the magnetometer will:(A) increase by 19% (B) increase by 11%(C) decrease by 19% (D) decrease by 21%

Q.17 A magnet is suspended in such a way that itoscillates in the horizontal plane. It makes 20oscillations per minute at a place where dipangle is 30° and 15 oscillations per minuteat a place where dip angle is 60°. Ratio ofthe total earth's magnetic field at the twoplaces is:

(A) 8:33 (B) 39:16

(C) 4 : 9 (D) 9:32

Q.18 The tangent galvanometers having coils of thesame radius are connected in series. Acurrent flowing in them produces deflectionsof 60° and 45° respectively. The ratio of thenumber of turns in the coil is:

(A) (4/3) (B) 1/)13(

(C)

1313

(D) 1/3


Q.19 A certain amount of current when flowing in aproperly set tangent galvanometer produces adeflection of 45°. If the current be reduced bya factor of 3 , the deflection would :

(A) decrease by 30° (B) decrease by 15°(C) increase by 15° (D) increase by 30°

Q.20 The work done in rotating a magnet ofmagnetic moment 2 A-m2 in a magnetic fieldof 5 ×10–3 T from the direction along themagnetic field to opposite direction to themagnetic field is :(A) zero (B) 2 × 10–2 J(C) 2 × 10+2 J (D) 10–2 J

Q.21 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

25/4 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) 21/4 (B) 21/2

(C) 2 (D) 25/4

Statements type question :

Each of the questions given below consist ofStatement – I and Statement – II. Use thefollowing Key to choose the appropriateanswer.

(A) If both Statement- I and Statement- II aretrue, and Statement - II is the correctexplanation of Statement– I.

(B) If both Statement - I and Statement - II aretrue but Statement - II is not the correctexplanation of Statement – I.

(C) If Statement - I is true but Statement - II isfalse.

(D) If Statement - I is false but Statement - II istrue.

Q.22 Statement I : A freely suspended magnetpoints along north-south direction.Statement II : Since earth behaves as magnet.

Q.23 Statement I : Poles of a magnet can neverbe separated.Statement II : Since each atom of a magneticmaterial is a magnet in itself.

Q.24 Statement I : To protect any instrument fromexternal magnetic field , it put inside an iron box.Statement II : Iron is magnetic substance.

Q.25 Statement I : Reduction factor (K) of atangent galvanometer helps in reducingdeflection of current.Statement II : As reduction factor increaseswith increase of current.

Q.26 Statement I : The susceptibility of diamagneticmaterials does not depend upon temperature.Statement II : Every atom of a diamagneticmaterial is not a complete magnetic in itself.


LEVEL # 4(Question asked in previous AIEEE & IIT-JEE)

Q.1 A thin rectangular magnet suspended freely hasa period of oxcillation equal to T. Now it is brokeninto two equal halves (each having half of theoriginal length) and one piece is made to oscillatefreely in the same field. If its period of oscillationis T´, the ratio T´/T is – [AIEEE-2003](A) 1/2 (B) 2(C) 1/4 (D) 1/ 22

Q.2 A magnetic needle lying parallel to a magneticfield requires W units of work to turn it through60º. The torque needed to maintain the needlein this position will be – [AIEEE-2003]

(A) W (B) W23

(C) 2 W (D) W3

Q.3 The magnetic lines of force inside a bar magnet – [AIEEE-2003]

(A) Do not exist(B) Depend upon the area of cross-section of

the bar magnet(C) Are from south-pole to north-pole of the

magnet(D) Are from north-pole to south-pole of the

magnet

Q.4 Curie temperature is the temperature abovewhich – [AIEEE-2003](A) A paramagnetic material becomes

diamagnetic(B) A ferromagnetic material becomes

diamagnetic(C) A paramagnetic material becomes

ferromagnetic(D) A ferromagnetic material becomes

paramagnetic

Q.5 The length of a magnet is large compared to itswidth and breadth. The time period of itsoscillation in a vibration magnetometer is 2s.The magnet is cut along its length into threeequal parts and these parts are then placed oneach other with their life poles together. The timeperiod of this combination will be –

[AIEEE-2004]

(A) 2s (B) 32

s

(C) 2 3 s (D) 3

2s

Q.6 The materials suitable for making electromagnetsshould have – [AIEEE-2004](A) High retentivity and high coercivity(B) Low retentivity and low coercivity(C) High retentivity and low coercivity(D) Low retentivity and High coercivity

Q.7 A magnetic needle is kept in a non-uniformmagnetic field. It experiences–

[AIEEE-2005](A) a torque but not a force(B) neither a force nor a torque(C) a force and a torque(D) a force but not a torque

Q.8 Needles N1, N2 and N3 are made of aferromagnetic, a paramagnetic and adiamagnetic substance respectively. A magnetwhen brought close to them will –

[AIEEE 2006](A) attract N1 strongly, but repel N2 and N3

weakly(B) attract all three of them(C) attract N1 and N2 strongly but repel N3(D) attract N1 strongly, N2 weakly and repel N3

weakly

Q.9 Relative permittivity and permeability of a material

are r and r, respectively. Which of the following

values of these quantities are allowed for a

diamagnetic material ? [AIEEE 2008]

(A) r = 1.5 , r = 0.5 (B) r = 0.5 , r = 0.5

(C) r = 1.5 , r = 1.5 (D) r = 0.5 , r = 1.5


ANSWER KEY

LEVEL # 1

LEVEL # 2

Q.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Ans. D B A A B B A D C A A D A A D A A D C B C D C B AQ.No 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50Ans. A D C D A C A B B C C B B C B B B B A B D D A A BQ.No 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68Ans. A D C B A A C B D C C B B A A C A C

Q.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Ans. A C B C D B A B A A A C A A D A A D D B C C C C BQ.No 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50Ans. A A B B D C C A C C B A A C D C D C A D A A A C AQ.No 51 52 53 54 55 56 57 58 59 60 61 62Ans. A B B A D C A C B C C B

LEVEL # 3

LEVEL # 4

Q.No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Ans. D A B A D B A B A B C D B A A B B D B BQ.No 21 22 23 24 25 26Ans. C A A B C A

Q.No 1 2 3 4 5 6 7 8 9Ans. A D C D B B C D A

Documents

Magnetism Exercise