Magnetism and Matter Questions and Answers

21 The magnetic needle of a vibration magneto meter makes 12 oscillations per minute in the horizo ntal 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 inter changed the number of oscillations it takes per minute is 1 61 2 63 3 65 4 67

A uniform disc of radius R having charge Q distributed uniformly all over its surface is placed on a smooth horizontal surface A magnetic field B kx t where k is a constant r is the distance in metre from the centre of the disc and r is the time in second is switched on perpendicular to the plane of the disc Find the torque in N m acting on the disc after 15 sec Take 4kQ 1 S I unit and R 1m

origin d the work done to move a charged particle along closed path away from the region will not be zer 2 Two point charges of I C and 1 uC are separate by a distance of 100 A A point P is at a distance c 10 cm from the midpoint and on the perpendicula bisector of the line joining the two charges Th electric field at P will be a 9 NC 1 c 90 NC b 0 9 NC d 0 09 NC

c 6 28 x 10 m s 35 A particle with charge q is moving along a circle of radius R with uniform speed v The associated magnetic moment u is given by a 1 v R 2 b 4 d 3 14 10 m s qvR 1 c qvR 2 d 1 q vR 2 D with its

Two concentric coplanar circ loops 0 2 m and 2 m A time varying potential difference 4 2 5 t volt is applied to the larger loop Calculate current in the smaller loop sol The magnetic field at the centre O due to the current in the larger loop is B Hol 2R If p is the resistance per unit length then potential difference 4 2 5t B No 4 2 5t 2R 2 Rp resistance 2 R p r R so the field B can be taken almost constant over the entire area of the smaller loop I 4 2 5t the flux linked with the smaller loop is Bxr Ho 2R 2 Rp do Hor dt 4R p The corresponding current in the smaller loop is I then Induced emf e x 2 5 V 4 2 5t S r

neet prep High Yielding Test Series Part Test 6 magnetising fields Following graph has been plotted for 1 200 V B versus H Choose the wrong statement 2 100 V 3 50 V Contact Number 9667591930 8527521718 1 There is a limit of direct and reverse external magnetising field at which the magnetisation and hence the magnetic induction saturates 2 Even after removing the external magnetising field some residual magnetisation called retentivity is left over in the substance 3 On increasing the reverse magnetising field the magnetic field decreases to zero for a value of 4 150 V 167 A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5 0 ms at right angle to the horizontal component of the earth s magnetic field 0 30 10 4 Wb m2 The instantaneous value of the emf induced in the wire is 1 2 5 10 v 2 1 5 10 4 V 3 2 5 10 4 V 4 1 5 10 v

The area of a rectangular loop of wire is 3 0 x 10 m The loop is placed in a magnetic held that changes from 0 20 T to 0 80 T in 1 6 s The plane of the loop is perpendicular to the direction of the magnetic field What is the magnitude of the induced emf in that loop 2 8 x 10 V 011 10 V 3 0 10 V OOV O 18 10 V

What is the general expression for the acceleration v of a simple damped mechanical oscillator driven by a force Focos ut Derive an expression to give the frequency of maximum acceleration and show that if r sm then the acceleration amplitude at the frequency of velocity resonance equals the limit of the acceleration amplitude at high frequencies

At some location on earth the horizontal component of earth s magnetic field is 18 10 6 T At this location magnetic needle of length 0 12 m and pole strength 1 8 Am is suspended from its mid point using a thread it makes 45 angle with horizontal in equilibrium To keep this needle horizontal the vertical force that should be applied at one of its ends is 3 6 10 N 1 8 x 10 5 N 1 3 x 10 5 N 6 5 10 5 N

S and S are the two coherent point sources of light located in the x y plane at points 0 0 and 0 3X respectively Here is wavelength of light At which one of the following points givenas co ordinates the interference is maximum

in the figure a copper bar is in contact with a pair of parallel metal rails and is in motion with velocity v A uniform magnetic field is present pointing downward as shown The bar the rails and the resistor R are all in the same plane What is the reduced current through the resistor R 141 B R MMMM

The figure illustrate how B the flux density inside a sample of unmagnetised ferromagnetic material varies with Bo the magnetic flux density in which the sample is kept For the sample to be suitable for making a permanent magnet B R Question Type Single Correct Type 10Q should be large OR should be small 2 OQ and OR should both be large 3 OQ should be small and OR should be large Be

At a certain place the component Bo and the horizontal vertical tota at a mir 1 3 component Vo of the earth s magnetic field are equal in magnitude The total intensity at the place will be 1 Bo 2 B 3 2 Bo 4 2B0 11 Th is

neet prep Mini Test 15 Earth s Magnetism Contact Number 9667591930 8527521718 is tan plane inclined at an angle of 30 with and then it shows an angle of dip 0 Then tan fr magnetic meridian is 1 1 cos x a tan 2 1 sin x 3 1 tan x b tan 2 4 cos x

An electron and proton are in uniform electric field the ratio of their respective acceleration will be O Zero O Unity O The ratio of the masses of proton and electron O The ratio of the masses of electron and proton

A 13 7 kg mass is suspended on a 1 10 N m spring The mass oscillates up and down from the equilibrium position yeq 0 according to y t A sin wt o At time to 0 the mass is at 29 6 cm and moving unward at velocity 6 32 m s

58 On a ship sailing in pacific ocean where temp is 23 4 C A balloon is filled with 2L air what will be the volume of balloon when the ship reaches Indian ocean where temp is 26 1 C 1 12 01L 2 6 01L 3 2 01L 4 1 02L

Q 17 How will the conductor carrying current I rotate immediately after it is released in following three cases consider magnetic force only a Conductor carrying current I is placed symmetrically above poles of a fixed U shaped magnet figure a b Conductor carrying current I is placed symmetrically at a distance from a fixed current 1 carrying wire fig b c An insulated circular current carrying wire is held fixed in vertical plane Conductor carrying current lo is in the shape of a circle of diameter nearly equal to that of the fixed insulated circle The planes of the two circles are perpendicular to each other fig c with xy as common diameter Fixed N a S Fixed b 60

1 A moving coil galvanometer has 100 turns and each turn has an area 2 0 cm 2 The magnetic field produced by the magnet is 0 01 T The deflection in the coil is 0 05 radian when a current of 10 mA is passed through it Find the torsional constant of the suspension wire

al oxygen are 12 14 and 16 respectively among the following pairs of gases the pair that will diffuse at the same rate is 1 Carbon dioxide and nitrous oxide 2 Carbon dioxide and nitrogen peroxide 3 Carbon dioxide and carbon monoxide 4 Carbon dioxide and nitric oxide

The following data were obtained on a thin sheet of silicon steel Compute the hysteresis loss and eddy current loss at 60 Hz Frequency Hz Flux density T Magnetic loss W kg 1 1 1 5 1 1 25 25 60 0 669 0 401 0 791 0 419 0 791 0 411 0 4 0 8 1 2

In the following the most sensitive method to compare the magnetic moment of two bar magnets with a deflection magneto meter is A B C tan A null method tan A equidistant tan B equidistant

A dip needle lies initially in the magnetic meridian when it shows an angle of dip at a place The dip circle is rotated through am angle x in the horizontal plane and then it shows an angle of dip 9 Then tan 0 is tan 0 1 COS X 2 1 sin x 3 1 tan x 4 cos x

A thin wire of length and mass m is bent in the form a semicircle as shown Its moment of inertia about an axis joining its free ends will be x mar 19x x 4 22 MR J4x S 88MR 1 ml O Y 2 Zero 3 X ml 2 4 ml 2

A bar magnet has coercivity 4 x 103 Am It is desired to demagnetize it by inserting it inside a solenoid 12 cm long and having 60 turns What current should be sent through the solenoid

Two parallel rails with negligible resistance are 1 00E 1m apart and are connected by a 4 000 resistor The circuit also contains two metal rods having resistances of R 12 200 and R 20 000 siding along the rails see figure The rods are pulled away from the resistor at constant speeds v4 00m s and v2 00m s respectively A uniform magnetic field of magnitude 0 0100 is applied perpendicular to the plane of the rails Determine the current in the 4 00ohm resistor

19 A bar magnet of length 10cm and pole streng 20A m is deflected through 30 from the magnetic meridian If earth s horizontal component field is A m The moment of the deflecting couple is 320 4t 1 160 10 7 Nm 3 320 10 7Nm 2 320x107 Nm 4 160 10 7Nm

The area of hysteresis loop of a material is equivalent to 250 m When 10 kg material is magnetised by an alternating field of 50 Hz then energy lost in one hour will be if the density of material is 7 5 gm cm 1 6 104 J 3 3 x 10 1 2 6 104 erg 4 3 x 10 10 ar

A negatively charged particle is revolving is circle of radius r out of the following which on fig represents the correct direction of I and M L is angular momentum of particle and M magnetic moment of the particle 3 M M 2 4 M Q M LA I

4 29 A magnet 10cm long and having a pole strength of 2 Am is deflected through 30 from the magnetic meridian Th horizontal component of earth s induction is 0 32 10 T TH value of deflecting couple is A 16x 10 7Nm C 48x 10 7Nm B 32x 10 7Nm D 64 x 10 7Nm

Properties related to diamagnetism are given below select wrong statement 1 Diamagnetic material does not have permanent magnetic moment 2 Diamagnetism is explained in terms of eletromagnetic induction Diamagnetic substances have small positive magnetic susceptibility 4 Magnetic moments of different eletrons cancel each other RPMT 2010 umber of turns are 48 and area of coil is 4 x 102 m If intensity of

Select the incorrect alternative s When a ferromagnetic material goes through a complete cycle of magnetisation the magnetic suscept 1 has a fixed value 2 may be zero 3 may be infinite 4 may be nagative should have

74 A square coil of edge L having n turns carries a current i It is kept on a smooth horizontal plate A uniform magnetic field B exists in a direction parallel to an edge The total mass of the coil is M What should be the minimum value of B for which the coil will start tipping over a c Mg niL Mg AniL b d Mg 2niL 2Mg niL

4 42 A magnetic needle vibrates in the vertical plane perpendicular to the magnetic meridian Its time period is 2 seconds if the same needle vibrates in the horizontal plane and the time period is again 2 seconds what is the angle of dip at that place A 30 C 60 B 45 D None of the above

The primary origin of magnetism lies in 1 atomic current and intrinsic spin of electrons 2 polar and non polar nature of molecules 3 pauli exclusion principle

A circular loop of mass m and radius r lies on a table in x y plane as shown in figure A uniform magnetic field B is switched on along positive x axis The current in the loop so that loop just lift from table is B mg 2rB mg TUB mg ar B mg 4 TUB

A Column I with Colum shown in figure Match side a is placed on a frictionless horizontal surface A vertical force F is applied to edge as 200 A B Column I Mg Mg p Cube will move up F 4 2 F Mg 2 C F Mg Mg 4 D F q Column II r Cube will not exhibit motion Cube will begin to rotate and slip at A Normal reaction s a A p B q C s D r b A r B s C q D p c Aq B r C p D s d A s B p C r D q effectively at a 3 from A no motion 7 9 Moment of Inertia 47 Analogue of mass in rotational motion is a moment of inertia b torque c radius of gyration d angular momentu 48 The moment of inertia of a body depends upon

dgnet is broken into two equal pieces 23 Assertion For shown situation a small body A can be levitated in mid air if it is made of paramagnetic material A S be reduced to half Reason In non uniform external magnetic field paramagnetic material is attracted to regions of greater magnetic field

4 55 The two infinite plates shown in cross section in figure 4 268 carry amperes of current out of the page per unit width of plate Find the magnetic field at points P and Q P Q Figure 4 268

4 61 A vibration magnetometer consists of two identical bar magnets placed one over the other such that they are mutually perpendicular and bisect each other The time period of oscillation in a horizontal magnetic field is 4s If one of the magnets is taken away find the period of oscillation of the other in the same field from magr magnets Ans M 4 67 A resistivi consist and ne

agnet producing Find the couple apere is passed Ets plane o identical bar are mutually e period of 4 66 A magnet is suspended in the magnetic meridian with a untwisted wire The upper end of the wire is rotated through 180 to deflect the magnet by 30 from magnetic meridian Now this magnet is replaced by another magnet Now the upper end of the wire is rotated through 270 to deflect the magnet 30 from magnetic meridian Compare the magnetic moments of magnets Ans M M 5 8

a bar magnet of pole strength m and magnetic moment M is cut equally 4 times parallel t ts axis and 3 times perpendicular to its axis then the pole strength and magnetic moment o each piece are respectively m M 11 21 m M 21 m M 11 m M

The parameter of an equivalent circuit of a three phase induction motor affected by reducing the rms value of the supply voltage at the rated frequency is 1 rotor resistance

3 Two magnets A and B are identical and these are arranged as shown in the figure Their length is negligible in comparison to the separation between them A magnetic needle is placed between the magnets at point P which gets deflected through ar angle under the influence of magnets The ratio of distances d1 and d will be A d A 2 tan 0 1 3 B 2 tan 0 3 C 2 cot 0 1 3 D 2 cot 0 3 B

The angle of dip at a certain place on the earth is 45 The apparent angle of dip measured by a dip circle when its plane is at an angle 37 with the magnetic meridian is 45 tan 3 tan 1 1 Im 3 tan 1 5

A ferromagnetic material is placed in an external magnetic field The magnetic domains A increase in size B decrease in size C may increase or decrease in size D have no relation with the field Your Answer A Answer C

Maik Which of the following is not a vector quantity Magnetic field Magnetic susceptibility Intensity of magnetisation Magnetising field intensity hr n

A current carrying wire of length l is bent to form a circular coil of one turn After that it is again bent to form a circular coil of two turns Find ratio of magnetic moment of coils respectively Question Type Single Correct Type 1 1 2 2 1 4 3 2 1

A bar magnet is placed coaxially from a smal magnetic needle and frequency of smal oscillations of the needle is found to f rev s now bar magnet is reversed in direction and frequency of oscillations of the needle is found to be f2 f1 rev s The frequency of the needle if bar magnet is completely removed from this place and magnetic needle is allowed to oscillate only in earth s magnetic field is 2 ff 1 TS 4 dations 1 1 2 2

68 A toroid of n turns mean radius R and cross sectional radius a carries current I It is placed on a horizontal table taken as XY plane Its magnetic NCERT Exemplar moment m a is non zero and points in the Z direction by symmetry b points along the axis of the toroid m m c is zero otherwise there would be a field falling as large distances outside the toroid d is pointing radially outwards 1 3 r at