Magnetic Field Questions and Answers

The top and bottom faces of a rigid insulating box of dimensions axbxh and mass m are charged with uniform surface charge densities and respectively and the box is placed in a uniform horizontal magnetic field B Bj Assuming free space conditions and h negligibly small as compared to the dimensions a and b find how much velocity will the box acquire after the magnetic field is switched off 20abh B m 20abhB gabhB m gabhB

5 Aplane electromagnetic wave of frequency 25 MHz travels in free space along the x direction At a particular point in space and time E 3 3 j V m What is the magnitude and direction of B at this point

A ring of radius 20 cm has a total resistance of 0 049 A uniform magnetic field varying with time B 0 4t T is perpendicular to the plane of the ring A Induced current in the ring is 2 A 5 B The ring will be in tension C The ring will be in compression D The magnetic field due to ring at the center of the ring is in direction opposite to applied magnetic field

A 36 cm diameter circular loop of wire has a resistance of 70 2 It is initially in a 0 43 T magnetic field with its plane perpendicular to B but is removed from the field in 150 ms Part A Calculate the electric energy dissipated in this process Express your answer using two significant figures VAEO www HAY

A particle of mass 9 kg and charge 100C is projected with a speed of 10 m s at an angle 45 above the horizontal After travelling a horizontal distance of 0 5 m It enters into a region where in addition to gravity a uniform static horizontal electric field also exists Boundary of the region is vertical If after some time the particle returns to its original position then find the magnitude of electric field in newton columb

The coercivity of a certain permanent magnet is 4 0 104 A m This magnet is placed inside a solenoid having 4000 turns m The current required to demagnetise the magnet completely is 10 A 16 A 18 A 20 A

A conducting wire bent in the form of a parabola y2 2x carries a current of 2 A The wire is placed in a uniform magnetic field Bras shown in fiqure The magnetic force on wire in newton is ym 167 87 167 2m x m

2 A long straight wire carries a current of 1 5 A A circular loop of wire lies immediately to the right of the straight wire as shown in the figure The loop has a radius of R 0 05 m and carries a current of 12 2 A Assuming that the thickness of the wires is negligible find the magnitude and direction of the net magnetic field at the centre C of the loop uo 4 X 10 7 Tm A I I2 C R

There is a uniform magnetic field B in a circular region of radius R as shown in the figure whose magnitude changes at the rate dB dt The emf induced across the ends of a circular concentric conducting arc of radius R having an angle 0 as shown ZOAO 0 is dB 0 A R 2 2 0 2 C R2 dt dB dt dB B R 2 dt D none of these X X x RA fit AXX XIX x R

Magnetic Induction Due to a Tube with a Slit A long thin walled tube of radius R with a longitudinal slit of width h carries a current I Find the magnetic induction inside the tube at a general point distant r from slit Take h R 4 S

Which given figure O 1 Infinitely long wire kept perpendicular to the paper carrying current inwards B A C 1 2 D 1 Net force on the loop is non zero 2 Net torque on the loop is zero 3 Loop will rotate clockwise about axis 00 when seen from O 4 Loop will rotate anti clockwise about axis 00

An infinitely long current carrying thick cylindrical conductor has a cylindrical canty of radius The axis of the cylindrical cavity is at a distance from the axis of the cylindrical conductor A current with current densim flows along the length of the conductor The magnetic field at a point P at a distance 2R from the axis of the cylinder is point P is on the plane containing both the axes POR A magnetic field at Pis B magnetic field at P is o C magnetic field on the axis of the cavity is non zero D magnetic field on the axis of the conductor is non zero Your Answer BD Answer BCD Solution When we fill the cauty with same curent density then magnetic field at 7 3x1 Direction is to the plane S

5 In a mass spectrometer used for measuring the masses of ions the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B If V and B are kept constant the ratio charge on the ion will be proportional mass of the ion to a 1 R2 c R b R d 1 R 2007

Determine the y and z component of the force experienced by a charge of 4C moving with velocity v 31 43 k m s in an electromagnetic field given by E 31 2kv m and B 1 3k T A B C D 40 N 4 N 11 N 11 N 44 N 4 N 10 N 10 N

in a 12A circular loop of radius a carrying a current i is placed two dimensional magnetic field The centre of the loop coincides with the centre of the field figure 34 E4 The strength of the magnetic field at the periphery of the loop is B Find the magnetic force on the wire a B

9 Three magnets of same length but moments M 2M and 3M are arranged in the form of an equilater triangle with opposite poles nearer the resultar magnetic moment of the arrange ment is 1 6M 3 3M 2 zero 3 2 4 M

30 Six point charges are placed at the vertices of a of side 1 m as shown in figure Net electric hexagon field at the centre of the hexagon is q q 1 Zero q O 9 5 q 9 6q 2 4 EO 4 q

0 20 A 14 The circuit below is based on Faraday s experiment of Electromagnetic Induction Study the circuit When the switch is turned on what will happen to the pointer of the ammeter 2 A The ammeter will show constant deflection to one side indicating steady current B The ammeter will momentarily show deflection to one side before coming back to zero C The ammeter will show continuafus alternating deflection on both sides D The anneler will not show inry deflection for 8 hours every day What is the electrical

5 points In the Hall sensor shown the electric potential UHall is measured and the left face is found to be at a higher potential than the right face What sign are the charge carriers in this material Justify with a figure or by annotating this one UHall B

M 1 6 b 2 b C 2 b 43 A wire PQR is bent as shown in figure and is placed in a region of uniform magnetic field B The length of PQ QR A current I ampere flows through the wire as P shown The magnitude of the force on PQ and QR will be a Ble o b OD 100 0 B16 B d Po I 2 b d00 R I O

MOVING CONDUCTING ROD IN EARTH S MAGNETIC Assume angle of declination is zero Case I Placed Horizontally and moves in horizontal plane E W direction B cuts If its ends in NS direction B cuts Case II Hold vertically and moves in horizontal plane E W line BH cuts If it moves on Dynamic emf If its ends in Dynamic emf 1 N S line No flux cutting No Dy EMI Case III Placed horizontally and allow to fall under gravity in vertical plane E W direction B cuts Dynamic emf ed B vl e vl 1 BV NS direction No flux cutting No Dy EMI 1 ed B ve

5 Assertion In electric circuits wires carrying currents in opposite directions are often twisted together Reason If the wire are not twisted together the combination of the wires forms a current loop

Two parallel frictionless rails are kept on a horizontal surface An ideal inductor having inductance Land a capacitor having capacitance C are connected to left ends of the rails as shown in figure In the space there exists a uniform magnetic field B into the plane of paper Arod AB having mass mand length is made to slide over the rails with a constant speed V by means of some external force which is in horizontal plane and perpendicular to the length ofrod as shown below Neglect the resistance of connecting wires and the rod AB 000000000 XXXXXX X X X X X X X X X X Here co X X X X XXX XXX XXXXXX XXXXXX C q t Bev C 1 cost 1 XXXXXX XXXXXX XXXXXX X X X X Xxxxx X X X X XXXXXX X Charge appearing on capacitor varies as A q t Bv Csinot B IN B q t Bv Ccos ot D q t Bv C 1 sin cot

11 Assertion Iron filings that have been sprinkled on to a cardboard collect in concentric circles when current is sent through a long wire which is normal to the plane of cardboard Reason An infinitely long wire has magnetic field lines in form of concentric circles

15 A magnet of length 2L and moment M is axially cut into two equal halves P and Q The piece P is bent in the form of semi circle and Q is attached to it as shown Its moment is N a C M TU M 2 2 P b d S N M 2 M 2 E Q S

6 A particle mass m and positive charge q is projected from the origin at t 0 with a velocity v A magnetic field Bexists in space Column II gives and Band Column I specifies some attributes of the path of the particle match them Column I A The radius of circular or helical path is qB B The maximum x co ordinate of the path of particle is qB C The minimum time taken to reach the maximumz co ordinate is m qB D The path is a straight line A a p r s t b p r c p r s t d q B a p s t b p r c p r t d q C a p r s t b p r t c p r s d q t D a p r s t b r c s t d q Column II p v vi B Bj g V B R1 r v x i R R B s v vi v x 7 B Ri B R R 1 2 1 2 2 2 v v i B B

Marks Obtained 0 0 Time spent 359 sec A uniformly charged ring of radius 0 1m rotates at a frequency of 10 rps about its axis The ratio of energy density of electric field to the energy density of the magnetic field at a point on the axis at distance 0 2m from the centre is in form X x 10 Find the value of X Use speed of light c 3 x 10 m s n 10 Your Answer 1 11 Answer 9 0 18 Solution Energy density of E field and energy density of B field 2 Po 4

E 2 0 1 0 150 50 50 1 0 2 0 150 A m The figure gives experimentally measured B vs H variation in a ferromagnetic material The retentivity co ercivity and saturation respectively of the material are 1 150 A m 1 0 T and 1 5 T 2 1 0 T 50 A m and 1 5 T 3 1 5 T 50 A m and 1 0 T 4 15T 50 A m and 10 T

A square wire frame is hinged about one of its sides AB Which of the following magnetic fields can hold it in equilibrium in horizontal position shown It has a mass of 500 g ya J Answer A B C Your Attempt B side 2m 3 5 k 3 2k 2 k Rate this question Correct answer

Two short magnets each of length 4 cm and pole strengths 5x10 3 amp metre and 10x10 3 amp metre are placed along the same line with like poles facing each other The distance between the centres of the magnets is 40 cm The magnetic induction at the centre of the line joining two magnets is A 5x10 9newton amp metre B 10x10 9newton amp metre C 15x10 9newton amp metre D 20x10 9newton amp metre Answer A Solution

A ball of mass 0 2 kg moving with a velocity 10 m s hits a bat normally and returns with a velocity 20 m s If the duration of impact is 0 01 s find the average force exerted by the bat on the ball

A laboratory has very strong magnetic field upwards I e towards the celling An electron gun is fired towards a wall The electron will Ceiling II Right Magnetic field Electron gun Left A Hit the other wall along the same line B Hit the ceiling C Hit the ground D Hit the wall on the left side of the shooter

4 51 A wire carrying current i has the configuration as shown in figure 4 266 Two semi infinite straight sections both tangent to the same circle are connected by a circular arc of central angle 0 along the circumference of the circle with all sections lying in the same plane What must be for B to be zero at the cenre of the circle R Figure 4 266

A uniform magnetic field B 0 5 T exists in a circular region of radius R 5 m A loop of radius R 5 m encloses the magnetic field at t 0 and then pulled at uniform speed v 2 m s in the plane of the paper Find the induced emf in V in the loop at time t 3 s

A circular loop of radius R 20 cm is placed in a unorm magnetic field B 2T in x y plane as shown in figure The loop carries a current i 1 0 A in the direction shown in figure Find the magnitude of torque acting on the loop YA 45 B

A very long bar magnet is placed with its north pole coinciding with the centre of a circular loop carrying an electric current i The magnetic field due to the magnet at a point on the periphery of the wire is B The radius of the loop is a The force on the wire is

Q 44 A wire carrying current I is laid in shape of a curve which is represented in plane polar co ordinate system as r b 0 for 0 0 2 TU y Here b and care positive constants is the angle measured with respect to positive x direction in anticlockwise sens and r is distance from origin see figure Calculate th magnetic field at the origin due to the wire O

A magnet performs 20 oscillations per minute in a horizontal plane where angle of dip is 60 and the earth s total field is 0 3 G At another place where total field is 0 6 G the magnet performs 15 oscillations per minute The angle of dip at the second place will be cos COS cos IN 2 14 1 9

1 Three charged particles their sign are shown move along the path in a as shown In each of three cases state whether the potential energy increases or decreases A B What is the work done by the field of a nucleus in a complete circular orbit of the electron and what if the orbit is elliptical

A particle of mass m and charge q has an initial velocity If an electric field E E and magnetic field B B i act on the particle its speed will double after a time 3mu 2mu 3mu zmu

A particle with charge q is projected successively along the x and y axes with same speed v The force on the particle in these situations are qvB 3 4k qvB 31 respectively Find the unit vector in direction of B

A circular turn of radius 1 m revolves at 60 rpm about its diameter aligned with the x axis as shown in the figure The value of o is 4 x 10 7 is Sl unit If a uniform magnetic field intensity 1072 is applied then the peak value of the inducted voltage Vtum in volts is m ZA TH est Vturn X

10 Suppose that two objects A and B are moving with velocities and each with respect to some common frame of reference Let A represent the velocity of A with respect to B Then a VAB VBA 0 b VAB BA 0 d Al Rain is falling vertically with a speed of 30 ms a 46 47

A uniform ring of mass m and radius R carrying current Io is lying in the x y plane in vaccum with centre at origin A uniform external magnetic field strength B Bo 21 23 5k Tesla is switched on at t 0 here Bo constant Gravity is neglected If the ring can freely rotate then Initial angular acceleration of ring is 4 21 BOTT m

A small satellite of mass m is revolving around earth in a circular orbit of radius o with speed v At certain point of its orbit the direction of motion of satellite is suddenly changed by angle cos 3 5 by turning its velocity vector such that speed remains constant The satellite consequently goes to elliptical orbit around earth The ratio of speed at perigee to speed at apogee is a 3 b 9 c 1 3 d 1 9

O a O b O O d Q23 C Which of the following is not equal to a Henry volt second coulomb volt second coulomb volt second ampere a b c d joule second coulomb

A non conducting cylindrical shell of radius R is placed in uniform magnetic field The axis of the cylinder is parallel to the direction of magnetic field A hole is drilled in cylinder and a particle having charge q and mass m is projected with velocity vo perpendicular to magnetic field and directed towards the axis of cylinder as shown in diagram The particle collides elastically with inner wall of the cylinder and rebounds A The minimum no of collisions after which it will emerge is two B The maximum speed vo for which it can come out is Vo 3 qBR m C The minimum time in which it can come out will be D If the particle is projected with a velocity v 3 qBR where Vo m m qB 3 it will come out after five collisions X X X X X X X X X X X X XXXX XXX xxx 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 y xxx X xxx Vo XXX XX xxxx XXXXXXXXX qm XXXXXXX

1 An infinite uniform current carrying wire is kept along z axis carrying current lo in the direction of the positive z axis OABCDEFG represents a circle where all the points are equal spaced whose centre at point 4 m 0 m and radius 4 m as shown in the figure B de Holo in S 1 unit k DEF then the value of k is A F 4m Qm B D X

21 An infinite uniform current carrying wire is kept along z axis carrying current lo in the direction of the positive z axis OABCDEFG represents a circle where all the points are equal spaced whose centre at point 4 m 0 m and radius 4 m as shown in the figure B de Holo in S 1 unit k DEF then the value of k is A F 4m Qm B E D

The shaded portion is one quadrant of a cylindrical space A long current carrying conductor is placed as shown in the figure which is along the axis of the cylindrical space Which of the following is are correct Region 1 is dotted region 2 is shaded A Magnetic flux through the region 1 is zero B Magnetic flux through the region 2 is zero C Magnetic flux through the region 2 is Hoih 2 D Magnetic flux through the region 1 is