Magnetic Field Questions and Answers

A cylindrical cavity of diameter a exists inside a cylinder of diameter 2a shown in the figure Both the cylinder and the cavity are infinitely long A uniform current density J flows along the length If the magnitude of the magnetic field at the point P is given by HoaJ the value of N is N 5 2a

c B is non zero in all cases The figure shows a long straight wire carrying a current I along the axis of a circular ring carrying a current I2 Identify the correct statement a Straight wire attracts the ring b Straight wire attracts a small element of the ring c Straight wire does not attract any small element of the ring d None of the above figure shows a wire frame in xy plane carrying a current I The 12

This is from electromagnetic induction ncert Please give a detailed solution of d part Why will polarity of A be pos tive Will the poles be induced in this coil Both are comi ng towards it I m not able to judge the increase or decreas e in magnetic flux and hence direction of current Please e plain the concept behind this question UKE 0 0 AMPLE 6 5 d Predict the polarity of the capacitor in the situation described by Fig 6 9 S A B FIGURE 6 9 2021 S Solution a No However strong the magnet may be current can be induced only by changing the magnetic flux through the loop b No current is induced in either case Current can not be induced by changing the electric flux c The induced emf is expected to be constant only in the case of the rectangular loop In the case of circular loop the rate of change of area of the loop during its passage out of the field region is not constant hence induced emf will vary accordingl

C Find the maximum torque on a galvanometer coil 5cm x 12 cm of 500 turns when carrying a current of 10 mA in a field where the flux density is 0 1 weber m

The end points of a current carrying wire lie on the x axis and y axis as shown in the figure The magnetic force on the wire is y m X XX X XX O 10 N O 20 N O 30 N O Zero X x xox X 2A 0 3 X X 4 0 B 2 0 T X x m

The penstock is used as a conduit between Answer A hydro station The dam and a turbine in the B drain The turbine and the discharge The heat exchanger and the C turbine None of these

A short bar magnet is placed in a uniform magnetic field such that its axis makes an angle of 60 with the direction of the field The strength of the magnetic field is 0 08 T If the work done in moving the bar magnet from this position to the most unstable position is 0 048 J the magnetic moment of the bar magnet is A 0 2 A m 2 B 0 27 A m C 0 32 A m 2 D 0 4 A m

A particle of mass m and charge q initially at rest is accelerated by a potential difference V to a velocity v directed towards south The particle enters a region in which both a magnetic field B and an electric field E exist The magnetic field is uniform and is directed eastward and the electric field is in the vertically downward direction The particle is found to travel in this region of electric and magnetic field without being deflected from its original trajectory One can conclude that A V B V mE2 2qB 2mE qB E C V qB

section of radius R is suspended from a rigid support as shown in the figure A light and small coil of 300 turns is wrapped tightly at the left end of the rod where uniform magnetic field B exists in vertically downward direction Air of density p hits the half of the right part of the rod with velocity V as shown in the figure What should be current in clockwise direction as seen from O in the coil so that rod remains horizontal Give answer in mA Given 2 TRB 1 LvV P 5 B 1 2 70 0 Air

No 135 A semicircular wire is moving with uniform velocity in a uniform magnetic field as shown in figure Hence the wire becomes A Positively charged at end A C B Positively charged at end B

14 A rod of length m moves in x y plane with a velocity v 21 31 m s in a magnetic field B i 1 K T The magnitude of induced e m f e along the rod is Inesangen 1 12 V 3 17 V YA poik 0 4m rod 3m 0 X 2 15 V 4 1 V roidy Jenisos

Exercise 7 Change the following sentences into passive voice 1 He told me a secret 2 Mr Sudhir taught us English

0 1 C kg is projected in uniform magnetic field The particle moves in m A point charge of specific charge magnetic field such that its position vector at any instant is given by F 3 sin ti 3 cos tj 4tk Select correct statements from following A Magnetic field in space is 10T B The distance traveled by the particle in 5s is 20m C Power of magnetic force is zero D The radius of curvature of the path is 3m

The figure shows a wire sliding on two parallel conducting rails placed at a separation I A magnetic field B exists in a direction perpendicular to the plane of the rails what force is necessary to keep the wire moving at a constant velocity v X X X X X X X X X X X X X X X X X X X X x XX X X X X X X X X X X X X X X X X X E xxxxxxxxxxxxxxxxx X X X X X X X X X X X X X X X X X X X X A B C B i v R X X 2B i v R B i v 2R X X X X X X X X X X X X X X

A flux quantum fluxoid is approximately equal to 2x107 gauss cm A type II superconductor is placed in a small magnetic field which is then slowly increased till the field starts penetrating the superconductor The strength of the field at this point is 2x10 T x10 gauss A The penetrating depth of this superconductor is

QThe figure shows a wire sliding on two parallel conducting rails placed at a separation I A magnetic field B exists in a direction perpendicular to the plane of the rails what force is necessary to keep the wire moving at a constant velocity v X X X X X X X X X X X X X X X X X X X X XX X X X X X X X X X X X X X X F xxxxxxxxxxxxxxxxxxx X X X X X k X X X X X X X X X X X X X X X X X X X X

3 The value of coefficient of mutual induction in two coils can be increased by 1 placing the coils mutually perpendicular 2 keeping the coils near to each other 3 keeping the coils considerably apart 4 winding the core on the common iron magnetic material and insulating them A transistor is operated in common emitter 38 fi qui 39 1 a 2 a 3 queferi a R 4 ff sferat att ta sfera A de privad to n

The wheels of a wagon can be approximated as the combination of a thin outer hoop of radius r 0 368 m and mass 4 89 kg and two thin crossed rods of mass 7 37 kg each A farmer would like to replace his wheels with uniform disks t 0 0588 m thick made out of a material with a density of 7830 kg per cubic meter If the new wheel is to have the same moment of inertia about its center as the old wheel about its center what should the radius of the disk be A rd n

A wooden stick of length 3 m is rotated about an end with constant angular velocity 2 rad s in a uniform magnetic field 5 T perpendicular to the plane of motion If upper one third of its length is coated with copper the potential difference across the copper length of the stick is X X X X X 3 m X 125 V 25 V 250 V X Copper X X Wood X X X X X X X X X

e displacement of a particle of the medium due to a wave moving in the positive z direction is given by y 1 att 2 second where and y are in metre The velocity of the wave in m s is 1 z 1 by y 0 5 1 1 at time

A smooth insulating ring of radius R with a bead having charge q is placed horizontally and in a uniform magnetic field of strength B and perpendicular to the ring plane Starting from t 0 the magnetic field is changed to B t B at where a is a positive constant The contact force between the ring and bead as a function of time is Neglect gravity aq Rt 1 3 m 2B at aq Rt B at 4m 2 4 aq Rt 4m 2B at 4aq Rt m 2B at

diagram represents the variation of temperature T of two bodies x and y having same surface area with time t due to the emission of radiation Find the correct relation between the emissivity e and absorptivity a of the two bodies X 1 2 3 ex ey ax ay ex ey ax ay ex ey ax ay ex ey ax dy

16 A charged particle enters a uniformi magnetic field with velocity vector at an angle of 45 with the magnetic field The pitch of the helical path followed by the particle is P The radius of the helix will be 1 3 P 2n P 2 2P 2P

a conducting loop carrying current is placed in x plane a uniform magnetic field pointing into z direction is switched on the loop will have a tendenc to figure contact expand move towrads ve x axis

An a particle is accelerated by a potential difference of 10 V The change in its direction of motion if it enters normally in a region of thickness 0 1m having transverse magnetic induction of 0 1T is 1 30 2 60 3 45 4 0

An a particle is accelerated by a potential difference of 104 V The change in its direction of motion if it enters normally in a region of thickness 0 1m having transverse magnetic induction of 0 1T is 1 30 2 60 3 45 4 0

inscribed in a circle of radius a metre If i ampere is the current flowing in the wire then the magnetic flux density at the centre of the circle is O a Hoi tan 2 a n Moni tan 2 a n 2 ni Ho tan a ni lo tan k TT n

A current carrying circular loop of Radius R is placed in a uniform magnetic field Bo tesla in x y plane as shown in figure The loop carries a current i 1A in the direction shown The torque acting on the loop is 1 R B 2 1 2 TR B 1 1 2 3 TR B 1 1 2 TR B i AY 45 B X

magnetic field is present as shown Ignore gravity Magnetic field During its motion inside the chamber a the force on the electron remains constant b the kinetic energy of the electron remains constant c the momentum of the electron remains constant d the speed of the electron increases at a uniform oto

A particle of mass m 1 6x10 27 kg and charge q 1 6 x 10 Centers a region of uniform magnetic field of strength 1 T along the direction shown in figure The speed of the particle is 10 m s 1984 8M E 45 XX x x x X x x

A plane of a dip circle is in the geographical meridian and the apparent angle of dip is 30 if dip circle is placed perpendicular to geographical meridian the apparent angle of dip is 60 The angle of declination at this place is A B funt ad 30 af aff tan 2 tan 3 C tan 3 D tan 3 Your Answer 60

An electron is executing uniform circular motion in a uniform magnetic field B If magnetic moment is M Select incorrect option A MxB 0 THE BE fafa far B M B 0 C M B 0 D Both 1 2 1 2 GTA Your Answer A

An electron is moving vertically downward deflection of electron due to earth s horizontal magnetic field is towards A East ad an eik B West RR C North 3R 3R D South af antar Your Answer i fa get fa fact

coil with N turns is partially filled with a magnetic material The coil has a rectangular cross section with inner radius r outer radius r and height h The magnetic material has a relative permeability and is found between the radius r and rm in 1 the toroid as shown in the figure The rest of the toroid is filled with air Calculate the self inductance of this toroidal coil Upload your workings in the last question Top View air Hr air Hr b Tm Side View a b N turns 3D View

A dip needle in a plane perpendicular to the magnetic meridian will remain A Vertical B Horizontal C In any direction D At an angle of dip to the horizontal Answer A

bb Electric circuit is composed of three conducting rods MO ON and PQ as shown in figure The resistance of the rods per unit length is known to be 1 The rod PQ slides as shown in figure at a constant velocity v kept at 45 as shown in figure At t 0 rod PQ is at O The whole system is embedded in a uniform magnetic field B which is directed perpendicularly into the page Then induced electric current is P M O X X X 45 X B X Q N a Proportional to time t b Inversely proportional to time t c Proportional to square of time t d Independent of time t

100 The graph below shows the variation of a force F with time t on a body which is moving in a straight line Dependence of force on time is F t Initially body is at rest F N 30 20 10 0 1 2 3 4 5 t s If the speed of the object is 2 m s at 3 s the speed at 4 s will be approximately in m s a 2 5 c 7 8 0 b 6 5 d 3 1

A dielectric slab of thickness d is inserted in a parallel plate capacitor whose negative plate is at y 0 and positive plate is at y 3d The slab is equidistant from the plates The capacitor is given some charge As y goes from 0 to 3d A the magnitude of the electric field remains the same B the direction of the electric field remains the same C the electric potential increases continuously D the electric potential increases at first then decreases and again increases

07 An axle of truck is 2 5 m long If the truck is moving due north at 30 ms at a place where the vertical component of the earth s magnetic field is 90uT the potential difference between the two ends of the axle is a 6 75 mV with west end positive b 6 75 mV with east end positive d 6 75 mV with south end positive c 6 75 mV with north end positive 58 In the following circuit the bulb will become suddenly bright if M

Two parallel long straight conductors carrying currents and 31 in the same direction are Sri Chaitanya Educational Institutions India separated by a distance of 4 cm From wire with lesser current they will produce zero magnetic field at a distance of

7 In the figure shown a charge q moving with a velocity v along the x axis enter into a region of uniform magnetic field The minimum value of v so that the charge q is able to enter the region x b Y 3 qBb m qB b a xxx 4 qBa m qB b a

The region between x 0 and x L is filled with uniform magnetic field Bok A particle of mass m positive charge q and velocity voi travels along x axis and enters the region of the magnetic field at origin Neglect gravity The particle emerges from the region of magnetic field with its velocity at an angle 30 to its initial direction If the magnetic field is reduced to half of the initial value then t angle of deviation will become A sin 1 4 B 60 D sin 1 2 C 90

Two identical conductors P and Q are placed on two frictionless rails R and S in a uniform magnetic field directed into the plane If P is moved in the direction shown in figure with a constant speed then rod Q P Q R XV X X B X X 1 will be attracted towards P 2 will be repelled away from P 3 will remain stationary 4 may be repelled or attracted towards P A square coil ACDE with its plane vertical is

A charged particle with specific charge s moves undeflected through a region of space containing mutually perpendicular and uniform electric and magnetic fields E and B When the electric field is switched off the particle will move in a circular path of radius 1 E Bs 2 Es B 3 Es E B s

Two identical short bar magnets each having magnetic moment M are placed a distance of 2d apart with axes perpendicular to each other in a horizontal plane The magnetic induction at a point midway between them is A B C D M H V2 1 4 4 Hoo 3 4 2440 Ho 4 5 M 13 M d M d3

The magnetic field produced due to a circular wire at its centre is a at 45 to the plane of the wire b at 60 to the plane of the wire c in the plane of the wire

2 A vertical wire carries a current in upward directon If an electron beam sent horizontally towards the Wi then it will deflected 1 vertically downwards and perpendicular to the plane of the paper 2 vertically upwards and perpendicular to the plane of the paper 3 In the plane of the paper 4 No deflection Oi N

a BL Wb c 2 B L Wb b 2 B L Wb d 4 B L Wb 3 A cylindrical bar magnet is rotated about its axis as shown in figure A wire is connected from the axis and is made to touch the magnet cylindrical surface through a contact Then Axis N 0 a a direct current flows in the ammeter A b no current flows through the ammeter A c an alternating sinusoidal current flows through the ammeter A with a time period T 2 2x 0 d a time varying non sinusoidal current flows through the ammeter A ab CL at A B sh a b c d 6 The area Nin a b d

There are two statement statement 2 points 1 for a long solenoid the magnetic field at the end is half of that in the middle of the solenoid statement 2 If the current in parallel wires are in same direction then the force between them is repulsive Which option is more correct O O Statement 1 is correct Statement 2 is incorrect Statement 1 is incorrect Statement 2 is correct Statement 1 Statement 2 are correct Statement 1 Statement 2 are incorrect

66 A hollow conducting pipe of radius 15 cm is carrying current of 2 A Magnetic field due to this hollow conductor is zero at a distance x from the axis of conductor Then x may be 2 16 cm 4 15 6 cm 1 10 cm 3 20 cm