Magnetic Field Questions and Answers

A wire ed of length and mass m is sliding 2 without friction on conducting rails ax and by as shown The vertical rails are connected to each other with a resistance R between a and b A uniform magnetic field B is applied perpendicular to the plane abcd such that cd moves with a constant velocity of a mgR BE R ww mgR B212 3 mgR B 0 mgR B af van ed fuer 1 mgR BO da x by fan for free b grada Babc fed alle Brit R 2 mgR B 2 mgR B D mgR B 0

Two concentric circular loops one of radius R and the other of radius 2R lie in the xy plane with the origin as their common center as shown in the figure The smaller loop carries current I in the anti clockwise direction and the larger loop carries current 1 in the clockwise direction with I 21 B x y denotes the magnetic field at a point x y in the xy plane Which of the following statement s is are correct y 1 12 2R X A B x y is perpendicular to the xy plane at any point in the plane B B x y depends on x and y only through the radial distance r C B x y is non zero at all points for r R D B x y points normally outward from the xy plane for all the points between the two loops x y

23 A cycle wheel of radius 0 5 m is rotated with constant angular velocity of 10 rad s in a region of magnetic field of 0 1 T which is perpendicular to the plane of the wheel The EMF generated between its center and the rim is 2 Points 0 25 V 0 125 V 0 5 V Zero

Q10 Given two parallel wires carrying current I and I are kept at a distance d apart Obtain the expression force exerted by one on the length of the another When this force will be attractive and when this force will repulsive

A circular loop of area 100 cm sits in the xy plane A uniform magnetic field B 0 2 J 0 5 k T is applied on it What is the magnetic flux through the loop a 0 005 Wb b 0 008 Wb c 0 007 Wb d 0 006 Wb

A physical quantity S is defined as B o where is electric field B is magnetic field and o is the permeability of free space The dimensions of S are the same as the dimensions of which of the following quantity ies A C Energy Charge x Current Energy Volume B D Force Length x Time Power Area

hly charged semi infinite conducting wire is placed along x axis as shown in figure such that one end at the origin Then electric field intensity at the point P will be Where is linear charge density of wire P 0 a 2 1 4 ea 00 2 4 2 4 a i 4

Which of the following statement is correct 1 The value of electric potential is same at every point inside a non concentric cavity created in a uniformly charged non conducting solid spherical charge distribution 2 Decreasing the separation between two point charges always increases their potential energy 3 The locus of all such points where the potential due to a short dipole is zero is a straight line 4 None of these

dB dt The magnetic flux density B is changing in magnitude at a constant rate of B A given mass m of copper drawn into a wire of radius a and formed into a circular loop of radius r is placed perpendicular to the field B The induced current in the loop is I The resistivity of copper is p and density is d then A i m dB 4 pd dt

2 A loop of irregular shape made of flex conducting wire carrying clockwise current is placed in uniform inward magnetic field such that its plane is perpendicular to the field Then the loop 1 Experiences force 2 Develops induced current for a short time 3 Changes to circular loop AAI 4 All of these

A long coaxial cable carries current the current flows down the surface of the inner cylinder radius a and back along the outer cylinder radius b as shown in Fig 7 40 b 1 netic field B FIGURE 7 40 a Refer to Example 7 13 a coaxial cable carrying current I down the inner conductor returning on the outer conductor Find the mag b Continuing suppose the outer conductor radius b is at potential V 0 and the inner conductor radius a is at constant potential Vo Find the potential V s for a b

If the peak emf produced by AC genera is 440 volt and coil of area 20 cm is rotated at the speed 1000 radian sec in 0 1 T magnetic field find the number of turns in coil O 2200 O 1100 O 4400 O 8000

There is a rod BC with a uniform charge per unit length 2 Point A is at a distance R from the point B on a line perpendicular to the rod BC AC makes an angle of with AB Find the electric potential at A A k2 In sin tan tan 0 B k2 In cos tan 0 C k2ln sec 0 tan 0 D k2 In cos eco tan 0 R B 0 C

PQ and RS are long parallel current carrying conductors separated by a certain distance M is the midpoint between them see the figure The net magnetic field at M is B Now the current in the wire PQ is switched off The magnitude of magnetic field at M becomes A 2B B B B C 2 D 3B 2 A P e M R S IA

A current I flows in an infinitely long wire with cross section in the form of a semi circular ring of radius R The magnitude of the magnetic induction along its axis is AIEEE 2011 A C HOI T R Hol 2 D B D Hol 27 R I

a particle of charge 1 C is projected into a magnetic field B 21 y k T with a velocity 41 27 4k ms it passes undeviatedly If it is now projected with a velocity 1 ms then the force experience is 9 N 18 N 3 N

A 20 eV electron is circulating in a plane at right angle to a uniform field of magnetic induction 2 x 10 4 Wb m The orbital radius of electron is nearly 7 5 cm 4 cm 9 cm 3 5 cm

A current i 5 amp flows through a thin wire as shown in the figure a Find the magnetic field produced by the current at point O in the figure b If there exists an external magnetic field B 141 14 T calculate the torque acting on the wire 20 cm H 10cm B

A charged particle is accelerated through potential Vo is subjected to a crossed electric field E and magnetic field B The field are adjusted such that the charged particle is not deflected The specific charge of particle is given by 2B V B 2V E 2V B E 2V E 03 B

A rectangular cube of 10 cm x 6 cm x 2 cm 21 placed in uniform magnetic field of 5 k T Magnetic flux through face ABCD is H D 10 cm B t 2 cm 6 cm 1 30 m Wb 2 3 m Wb 3 0 3 m Wb 4 zero winst Londer Achiever Course ALL PHASE su ABCD H 1 30 m Wb 2 3 m Wb 3 0 3 m Wb 4 10 cm x 6 cm x 2 cm 5 K T u afera form n 10 cm B ww 2 cm 0 cm X 1001CMD303119106

7 ALLEN Following figures shown the arrangement of bar 27 magnets in different configurations Each magnet Which has magnetic dipole moment M configuration has minimum net magnetic dipole moment a c SS 90 130 IS 1 In a 3 In c d BOUND 60 S 2 In b 4 In d Magnetic field at point P due to Allmant 29 teau 15 Sci f zarci fazura if any faz ca faya gun 24 a c 90 SIS 30 IS 1 a 3 c fet mit sur from b d B S 2 b 4 d 60 N

For the circuit shown in figure the direction and magnitude of the force on PQR is B 60 R A No resultant force act on the loop B ILB out of the page C 2 D ILB into the page ILB into the page

and 5 10 mare separated by a distance 0 5 m and carry currents 24 and 5 1A respectively The force between the loops due to mutual induction is r 1 e C H i C K 1 2 09 108 N 3 4 18 108 N X i 2 1 06 10 N 4 8 3 10 N

The ratio of the velocity of light in a medium to the velocity of light in a vacuum is If the ray of light is emerging from this medium into the air then the critical angle for this interface of medium and air will be 1 30 2 37 3 53 4 45

A man starts running a race with a velocity 2 5 m s When he starts running he finds the wind is blowing at an angle 450 with the track As he progresses on the straight horizontal track he finds wind is rotating with uniform angular velocity and by the time he completes the race wind rotates through an angle 45 If the wind always blows perpendicular to the s find the length of the race track and time of race is 10 In 2

Example A solid insulating sphere of radius I cm has charge 107 C distributed uniformly over its volume It is surrounded concentrically by a conducting thick spherical shell of inner radius 2 cm outer radius 2 5 cm and is charged with 2x 10 7 C What is the electrostatic potential in Volts on the surface of the sphere

Question NO 30 Phy Section A This section contains 35 SINGLE CORRECT TYPE questions Each question has 4 choices 1 2 3 and 4 out of which only on The magnetic flux linked with a coil at any instant t is given by 1022 50t 5 Wb The induced emf at t 2 s is O 10 V O 19 V O 5 V O Zero

The current in the windings on a toroid is 2 0A There are 400 turns and the mean circumferential length is 40cm The magnetic field inside the toroid is approximately 1 3 1 mT 3 mT 2 4 2mT 2 5 mT

SEN In the figure shown two infinitely long parallel straight current carry wires are spearated by a distance d the current in each wire is I Points A and B are in the plane of the wires Find the ratio of the magnetic field BA A and B at B d 2

Q 13 A long straight conductor having a circular cross section of radius 2 m carries a current its length such its magnetic field varies as B Kr 0 r 2m where K is a positi constant The slope of the current density j vs radial distance r at r m is aK find the value of a The Ho

1 When a magnetic compass needle is carried nearby to a straight wire carrying current then 1 the straight wire cause a noticeable deflection in the compass needle II the alignment of the needle is tangential to an imaginary circle with straight wire as its centre and has a plane perpendicular to the wire a I is correct b II is correct c both I and II are correct d neither I nor II is correct Which one 6

A positively charged particle of mass 2 6x10 12 kg and charge 5 5 105 C is perpendicular to a 3 5 T magnetic field If the particle has a speed of 6 0x104 m s the magnitude of the particle s acceleration is 4 4 10 2 m s 3 0x10 11 m s 5 0x10 12 m s 1 2 1010 m s 8 3x1021 m s

Particle A has a charge that is 10 times larger than the charge of particle B The magnitude of the electrostatic force exerted by charge A on the smaller charge B is 10 times larger than magnitude of the electrostatic force exerted by charge B on the smaller charge A O 100 times larger than magnitude of the electrostatic force exerted by charge B on the smaller charge A 10 times smaller than magnitude of the electrostatic force exerted by charge B on the smaller charge A none of the other answers is correct the same as the magnitude of the electrostatic force exerted by charge B on the smaller charge A O 100 times smaller than magnitude of the electrostatic force exerted by charge B on the smaller charge A

Two long parallel transmission lines 45 0 cm apart carry 20 0 A and 80 0 A currents Part A Find all locations where the net magnetic field of the two wires is zero if these currents are in the same direction Enter your answer as two distances in centimeters the first distance from the wire carrying 20 0 A and the second distance from the wire carrying 80 0 A Separate the values with a comma View Available Hint s X1 X2 Submit Part B VAE x1 x2 Find all locations where the net magnetic field of the two wires is zero if these currents are in opposite directions Enter your answer as two distances in centimeters the first distance from the wire carrying 20 0 A and the second distance from the wire carrying 80 0 A Separate the values with a comma VA O cm cm B

A velocity selector having uniform perpendicular electric and magnetic fields is shown in the figure Figure 1 The electric field is provided by a 150 V dc battery connected across two large parallel metal plates that are 4 50 cm apart Figure 1 of 1 150 V 4 50 cm Part A What must be the magnitude of the magnetic field so that charges having a velocity of 3 40 km s perpendicular to the fields will pass through undeflected Express your answer in teslas B Submit Part B AEO Submit Request Answer Provide Feedback Show how the magnetic field should point in the region between the plates In order for FB to be downward to oppose FE B must be into the page In order for FB to be downward to oppose FE B must be out of the page O In order for FB to be upward to oppose FE B must be out of the page O In order for FB to be upward to oppose FB B must be into the page T Request Answer Next

d In a direction that depends on the ratio of the loop radii 43 A coil has 2000 turns and area of 70 cm The magnetic fiel perpendicular to the plane of the coil is 0 3 Wb m and takes 0 1 sec t rotate through180 The value of the induced e m f will be a 8 4 V b 84 V c 42 V d 4 2V 4 A transformer is employed to

A quartz crystal is subjected to alternating electric field which leads to production of ultrasonic sound The thickness of crystal is 0 0005 m and density 2650 kg m3 Given Young s modulus Y 7 9 X 10 power 10 N m2

Each of the two identical magnets when suspended alone makes 30 oscillation per minute at a place The number of oscillation per minute if they are fixed at right angles and allowed to oscillate in the same field will be approximately Only One Correct Answer A B C 25 oscillation minute 30 oscillation minute 60 oscillation minute oscillation minute O

A thin circular loop of radius R carrying a uniform charge density is rotating about an axis passing through its center and perpendicular to its plane in the anti clockwise direction Its uniform angular velocity is w Find the vector potential and magnetic field at an arbitrary point on the axis of rotation Explain the consistency of your answers 6

5 Consider a triangular loop with vertices at 0 0 0 0 2 0 and 2 0 0 carrying a circulating current of 10A which flows in the positive y direction Find the magnetic field at the point 0 0 2 8

A bar magnet made of a material of magnetic moment 4 A m and a mass of 4 g The intensity of magnetisation of bar magnet will be Given density of material p 104 kg m 6 x 106 A m 12 x 106 A m 107 A m 106 A m

PASSAGE A quartz crystal is subjected to alternating electric field which leads to production of ultrasonic sound The thickness of crystal is 0 0005 m and density 2650 kg m3 Given Young s modulus Y 7 9 X 10 power 10 N m2 Read the following passage to answ ven questions correct options Marks 2 Calculate frequency of ultrasonic sound OPTIONS

No 16 A galvanometer has a resistance of 25 n and given a full state deflection for a current of 10 mA This galvanometer is to be modified to give range of 1 25A and 50 V what are resistances of shunt and high resistance needed to achieve this

tance arranged parallel on as shown in the charges of a to the separation Configuration their is U Now one ally reversed c forces Consider a metal sphere of radius r over which light beam of sufficiently high frequency is incident Due to photo emission metal sphere started to lose electrons The electric potential of a sphere varies with time as 1 3 v t 2 C 4 Gateway In moving from A to B along an electric 18 the work done by the electric field on a is 6 4 x 10 19 IfQ and Q are e surfaces then the potential differenc meg is placed inside a conducting OR and outer radius E 1 4V 3 Zero A uniform electric f 30 with the posit OA 2m and O is

A charged particle of charge 100 C and mass 10mg is projected in a uniform magnetic field of 25mT with a speed 10m s so that it moves on a circular path as shown in figure X X X xx XX A X X X B C X x X D xx X X X X X X X X The radius of the circle will be 4m 20m X XX X 40m 60m X X X

0 A current 10 A flows in a ring of radius ro 15 cm made of very thin wire The tensile strength of wire is equal to T 1 5 N The ring is placed in magnetic field which is perpendicular to plane of ring so that forces tend to break the ring Find the magnetic field at which the ring is broken X 1 0 2 T 3 1 0 T 2 0 6 T 4 1 2 T

1 If a beam of charged particles moving with speed 3 x 106 m s enters normally into a region of uniform magnetic field 90 mT and specific charge of each particle is 108 C kg then the radius of the circular path described by it will be 1 0 33 m 3 0 82 m 2 0 57 m 4 1 25 m

36 A region contains uniform electric field E in the positive y direction A charge q projected along the x axis with velocity V moves undeflected Then magnetic field B may be 1 5 3 k E R X 2 5 4

2 Figure shows a uniform magnetic field B normally into the paper If the charge q is incident on the boundary MN at an angle 60 as shown then the deviation produced to the path of the charge on emergence is Region of magnetic field is finite upto the left boundary MN only 1 60 q u M X X X X X Xd X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 60 N 2 240

3 The ratio of magnetic field at the centre of a current carrying circular wire of radius R and at a distance R from centre on its axis is 1 2 2 3 2 P 2 2 4 4 mincial 40