Magnetic Field Questions and Answers

uniform 42 In a certain region of space there exists a constant and magnetic field of induction B The width of the magnetic field is a A charged particle having charge q is projected perpendicular to B and along the width of the field If deflection produced by the field perpendicular to the width is d then the magnitude of the momentum of the particle is af 2 a c d 2d 4d a d qB qB b X X X 92 202 98 d a d 2d X xx X qB X a d

36 An a particle is moving along a circle of radius R with a constant angular velocity w Point A lies in the same plane at a distance 2R from the centre Point A records magnetic field produced by the a particle If the minimum time interval between two successive times at which A records zero magnetic field is t the angular speed w in terms of t is 2 2 a c t TC 3t b d 3t TC 2t

A charge in motion can exert force on a statinary bar mag net Conversely a bar magnet in motion can lead to a ford e on stationary charges 7 A charge in motion can exert force on a stationary magnet Conversely a bar magnet in motion can lead to a force on stationary charges This statement is NCERT Pg 213

ALLEN 5 A flux of Im Wb passes through a strip having 25 an area A 0 02 m The plane of the strip is at an angle of 60 to the direction of a uniform field B The value of B is 1 0 1 T 3 4 0 mT 2 0 058T 4 None of the above A 0 02 m f1 m Wb faa y un graf a af Bfm 60 m 1 0 1 T 3 4 0 mT 2 0 058T 4 3

uniform plastic cylinder of mass 2kg and length 0 5m has 20 turns of a light wire wrapped around its middle such that the v orms a rectangular coil with its plane containing the cylinder s central axis The cylinder is placed on a wedge inclined at 37 he horizontal such that the coil plane is parallel to the inclined plane If the coil carries a current of 0 2A find the vertical hagnetic field B that must be applied to maintain the cylinder at rest 0 5m 37

18 A square coil ABCD lying in x y origin A long straight wire passing through origin carries a current i 2t in the negative z direction the induced current in the coil is A D y C X

Find out the surface charge density at the intersection of point x 3 m plar and x axis in the region of uniform line charge of 8 nC m lying along the z axis in free space A 0 424 nC m 2 B 4 0 nC m 2 c 47 88 C m

4 16 A coil carrying a current I 10mA is placed in a uniform magnetic field so that its axis coincides with the field direction The single layer winding of the coil is made of copper wire with diameter d 0 1mm radius of turns is equal to R 30mm At what value of the induction of the external magnetic field can be coil winding be ruptured

3 A particle having charge q and mass m is projected from the origin with velocity vo in a uniform P k magnetic field B Bok at time t 0 If x t y t z t represent x y and z co ordinates of the particle at time t then select the correct option s 1 y t mv qB 2 x t 3 y t mvo qB mvo qB 4 z t vot 1 cos COS qBt m 1 sin qB m qBt m

5 A rectangular loop carrying current i is shown in the diagram If the magnetic field in the region is 2B1 Bo then choose the correct statement s av a G X VZ 1 Magnetic moment of the loop is ali 2 Magnetic moment of the loop is ali i 1 3 Torque on the loop is aliB k 4 Torque on the loop is K

3 2 mg 4 cube will not reach the point 2 A square conducting loop of side length L carries 23 a current I The magnetic field at the centre of the loop is 1 independent of L 2 proportional L 3 inversely proportional to L 4 linearly proportional to L 4 Na fang 2 PHAN T I m 2 L 3 L 4 L en were it

An electron travelling east to west enters a chamber having a uniform electrostatic field in south to north direction If electron is not deflecting from its straight line path then the direction of a uniform magnetic field B is fa 1 Vertically upward UU N 2 Vertically downward 3 Towards North you 4 Towards South NE yo VD f 10 A is

A stone is tied to a string of length and is whirled in a vertical circle with the other end of the string as the centre At a certain instant of time the stone is at its lowest position and has a speed u The magnitude of the change in velocity as it reaches a position where the string is horizontal g being ac celeration due to gravity is 1 u gl 2 u u 2gl 8 3 2gl bn leegi 4 2 u ge

A horizontal overhead powerline is at a height of 4m from the ground and carries a current of 100A from east to west The magnetic field directly below it on the ground is Mo 4 x 10 7 TmA 1 5 x 10 6 T northward 2 5 x 10 6 T southward 3 2 5 x 10 7 T northward 0 25 x 10 7 T southward

40 Given below are two statements labelled as Assertion A and Reason R Assertion A A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region If an electron is projected along the direction of the fields with a certain velocity its velocity will decrease Reason R Magnetic force on a charged particle moving in a magnetic field does no work on the particle Select the most appropriate answer from the options given below 1 Point Both A and R are true and R is the correct explanation of A

A potential difference of 400 volt is applied across the plates of a parallel plate capacitor plates being separated by 2 mm An electron projected vertically upward parallel to the plates with a velocity of 4 x 10 6m s moves undeflected between the plates The magnetic field in the region between the plates is 1 Point I

5 A circular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800 revolutions per minute in the earth s magnetic field B 0 5 gauss the maximum emf induced in the coil will be 1 0 29 V 2 5 8 V 3 1 158 V 40 58 V

A straight conductor and a conducting square loop of side a are kept as shown in the figure If the distance between the centre of the loop and the straight conductor is b the mutual inductance between them is A Hoa In 2 B C b a 2 b a 2 M b b a 2 In 2 b a 2 Ho In b a 2 2 a b a 2 b a 2 Ho D In b a a

A rod AB slides on V shaped wire with speed v in magnetic field B such that at an instant OA OB L If the induced emf in the loop OAB at this instant is given by Bvl then find the value of n A 90 B V

In the figure the circular loop has a current as shown When the current is switched on in the straight line conductor the loop will A be attracted towards the wire B be repelled by the wire C remain stationary bout avio morallel to the in

carrying a current I The radius of the innermost and outermost turns see figure are a and 4a respectively The expression for the magnetic moment of the spiral is et O 3 Nla a

The diagram shows two co planar conducting loops whose centres coincide If R then the mutual inductance will be 0 14012 4R O MOR 21 O H40 2R TULO 12

9 A solenoid at 1 5 metre length and 4 0 cm diameter posses 10 turn per cm A current of 5 ampere is flowing through it The magnetic induction at axis inside the solenoid is 1 2 x 10 Tesla 2 2x 10 Tesla 3 4x 10 Gauss 4 2 x 10 5 Gauss 4

A cylindrical conductor carries a constant current I out of the screen The line integral of the magnetic flux density vector B along a closed circular counter clockwise contour C not shown centered outside the conduc is 88880 10 conductor HOI ol greater than I positive and less than I zero

6 A circular arc of wire subtends an angle 2 at the centre If it carries a current i and its radius of curvature is R then the magnetic field at the centre of the arc is II 1

UNIVERSAL BOOK DEPOT 1960 1248 Electromagnetic Induction Three solenoid coils of same dimension same number of turns and same number of layers of windings are taken Coil 1 with inductance L was wound using a Mn wire of resistance 11 02 m coil 2 with inductance L was wound using the similar wire but the direction of winding was reversed in each layer coil 3 with inductance L3 was wound using a superconducting wire The self inductance of VITEEE 2008 the coils L L2 L3 are b L L L3 0 d L L L3 a L L L3 1 mado a L L L 0

8 Two parallel disks 60 cm in diameter are separated by a distance of 15 cm and completely surrounded by a large enclosure at 100 C The properties of the surfaces are T 540 C 0 7 T 300 C 0 5 What is the net radiant heat transfer with each surface Do not include back side exchange only that from the surfaces facing each other

A particle of negative charge q and mass m moving with velocity Vo enters a magnetic field B as shown in the figure The time for which the particles remains inside the magnetic field is X X 2 m qB qB qB X X n 20 20 X X

The rectangular loop shown in the figure is co planar with the straight infinitely long wire carrying current lo The magnetic flux through the loop is 03 Holoa 2T Holob 2T O Holoa 2T Holob In 2 a b

2 Figure shows two identical magnetic dipoles P and Q of magnetic moment M each placed at a separation 2d with their axes parallel to each other The magnetic field at midway M between the dipoles is Bo If one of them turned about centre by the magnetic field at M will be Assume short 2 bar magnets 1 3 S Bo 4 P 3Bo N 2d M 2 4 S 2 5B Q N

3 A circular coil is in y z plane with centre at origin The coil is carrying a constant current Assuming direction of magnetic field at x 25 cm to be positive direction of magnetic field which of the following graphs shows variation of magnetic field along x axis BA B a c Answer 0 BA B 0 x d b HONI 2R 3 b Direction of magnetic field at every point on axis of a current carrying coil remains same though magnitude varies Hence magnetic induction for whole the x axis will remain positive Therefore c and d are wrong Slope of the graph will be Magnitude of magnetic field will vary with x according to law Ho NIR 2 R x 3 2 Hence at x 0 B BA O dB dx O and when x B 0 3 NIR x 2 R x 5 2 It means at x 0 slope is equal to zero or tangent to the graph at x 0 must be parallel to x axis Hence b is correct and a is wrong Did you find it helpful

TO 45 O There exists a magnetic field in a cylindrical region of radius R The magnetic field is increasing at a constant rate a with respect to time The magnitude of induced electric field at a distance of from the axis of the cylindrical region will be 2 4 Mark for Review O ar hr min

34 A charged particle moves along a circle under the action of possible constant electric and magnetic fields Which of the following are possible 1 E 0 B 0 2 E 0 B 0 3 E 0 B0 4 E 0 B 0 gh Work

SI unit of electric current ampere is the current which when flows through each of two parallel wires spaced 1 m apart in vacuum and of infinite length will give rise to a force between them equal to O 1 N m O 4 x10 7 N m O 2x10 7 N m 110 7 Nim

An air cored solenoid having a length of 30 cm whose area is 25 cm and the number of turns is 500 And the solenoid has carried a current of 2 5 A Suddenly the current is turned off and the time is taken for it is 10 3 8 What would be the average value of the induced back emf by the ends of the open switch in the circuit Neglect the variation in the magnetic fields near the ends of the solenoid 1 5 5 V 2 4 5 V 3 6 5 V

Two infinite long parallel wires A and B carrying currer 10 A and 20 A respectively in opposite direction are placed at a separation of 30 cm The magnetic field will be zero at 10 cm from A between the wires 10 cm from B between the wires 30 cm from A outside the wires 30 cm from B outside the wires

A proton moving with a constant velocity passes through a region without change in its velocity If E and B represent electric and magnetic field respectively Then this region of space may not have O E 0 B 0 O E 0 B 0 O E 0 B 0 E 0 B 0

45 A point charge q is kept inside an electrically neutral estion the potential at point P would be estionpa ell with its outer surface spherical in shape then q 1 4 E OR q R ro r O centre of sphere 2 9 9 4 or P q 400

There exists a magnetic field in a cylindrical region of radius R The magnetic field is increasing at a constant rate a with respect to time The magnitude of induced electric field at a distance of R from the axis of the cylindrical region will be O O aR 2 aR 4

2 A1 Infinitely long hollow conducting cylinder with inner radius R 2 and outer radius R carries a uriform current density along its length The magnitude of the magnetic field B as a function of the radial distance r from the axis is best represented by A B C B B R 2 R R 2 R D B B R 2 R R 2 R

9 Two large vertical and parallel metal plates having a separation of 1 cm are connected to a DC voltage source of potential difference X A proton is released at rest midway between the two plates It is found to move at 45 to the vertical JUST after release Then X is nearly A 1 x 105 v B 1 1077 V D 1x 10 0 V C 1 x 10 v 9

0103 a mass of A particle having a 5 10 C The particle is given a of 10 ms in the presence of electric field kg carries a charge of an initial horizontal velocity E and magnetic field B To keep the particle moving in a horizontal direction it is necessary that B should be perpendicular to the direction of velocity and E should be along the direction of Both B and E should be along the direction of 2 velocity 3 Both B and E are mutually perpendicular and perpendicular to the direction of velocity B should be along the direction of velocity and E should be perpendicular to the direction of 4 velocity Which one of the following pairs of statements is possible a 1 and 3 c 2 and 3 b 3 and 4 d 2 and 4 AIPMT Mains

A rectangular loop of sides 25 cm and 10 cm carrying a current of 15 A is placed with its longer side parallel to a long straight conductor 2 cm apart carrying a current of 25 A What is the net force on loop

The electron in a hydrogen atom circles around the proton with a speed of 2 18 x 10 m s in an orbit of radius 5 3 x 10 m Calculate i the equivalent current and ii the magnetic field produced at the proton A rectangular loop of sides 25 cm and 10 cm carrying a current of 15 A is placed with

A charge q moving along the x axis with a velocity v is subjected to a uniform magnetic field B acting along the z axis as it crosses the origin O Trace its trajectory Does the charge gain kinetic energy as it enters the magnetic field Justify your answer i ii

The diagram below shows three circuits consisting of circular arcs half or quarter circles of radii r 2r and 3r as indicated and the straight line sections which are radial The three circuits carry the same current Rank them according to the magnitudes of the magnetic fields they produce at the centre of the circles starting with the greatest magnitude 2r 2r i A i ii iii B ii iii i C ii i iii D iii ii i 2r ii 2r r iii 2r

4 Increase in one and decrease in second 23 Consider a thin metallic sheet perpendicular to the plane of the paper moving with speed v in a uniform magnetic field B going into the plane of the paper see fig If charge densities o and o are induced on the left and right surfaces respectively of the sheet then Ignore fringe effects X X X X X X X X X X X X X X X X X X X XXXX X X XXXX X X X X X X X EVB 2 2 a VB a VB EVB 2

Question 14 Two concentric coplanner coils of turns n and n2 have radii ratio 2 1 respectively Equal current in both the coils flows in opposite direction If net magnetic field is zero at their common centre then n n2 is Only one option is correct A 2 1

1 The current voltage relation of a diode is giver by I e1000 V T 1 mA where the applied voltage V is in volts and the temperature T is in degree kelvin If a student makes an error measuring 0 01 V while measuring the current of 5 mA at 300 K what will be the error in the value of current in mA

Figure shows a block of mass m placed on smooth surface of wedge of mass M and inclination e Wedge is kept on smooth horizontal surface Find acceleration of wedge when system is released from rest M