Magnetic Field Questions and Answers

A current i ampere flows in a circular arc of wire whose radius is R which subtend an angle 3 2 radian at its centre The magnetic induction B at the centre is 2 40 R 3 oi 8R O Moi R O Moi 2R R x 2 Marks 4 1

Direction of induced current in a conductor moving in a magnetic field is given by Fleming s Right hand rule In this rule middle finger and fore finger point in the direction of 1 Magnetic field and motion of conductor respectively 2 Induced current and motion of conductor respectively 3 Induced current and magnetic field respectively 4 Magnetic field and induced current respectively

Ifo is the total cross section and f 0 0 being the angle of scattering is the scattering amplitude for a quantum mechanical elastic scattering by a spherically symmetric potential then which of the following is true Note that k is the magnitude of the wave vector along the direction a o 1 0 4 e x Imaginary part of f 0 0 b o 41 0 0 1 k 4 d 0 1

The rotational lines of the CN band system at 3883 4A is represented by a formula 25798 3 850m 9 0 068 m cm where m is a running number Calculate the values of the rotational constants B and B the location of the band head and the degradation of the band

A circular conducting loop C of radius 2m is located in the XOY plane such that its centre is at 0 0 0 Another circular conducting loop C of radius 2m is located at 0 0 4 such that the plane of C is parallel to the XOY plane A current of SA is flowing in each of these loops such that the positive Z axis lies to the left of the directions of the currents Find the magnetic induction B produced at 0 0 0 neglecting the mutual induction of the loops

X Question No 18 A rod of length 10 cm made up of conducting and non conducting material shaded part is non conducting The rod is rotated with constant angular velocity 10 rad sec about point 0 in constant magnetic field of 2 tesla as shown in the figure The induced emf between the point A and B of rod will be x 2cm 3cm B InCorrect Ax UnAnswer

A coil of 1000 turns of wire has a radius of 12 cm and carries a counterclockwise current of 15A If it is lying flat on the ground and the Earth s magnetic field points due north has a magnitude of 5 8 x 10 5 T and makes a downward angle of 25 with the vertical what is the torque on the loop

sec Telegra sec a substance of 5g cm then will be 10 6 moment 1 44 ts north pole of the neutral component of 2 19 Magnitude Magnetic moment of two magnets are equal M and are placed at an angle of 60 as shown in figure Then resultant magnetic moment of combination will be 1 2M 2 3 M M 2 4 3 1 M 3 60

A small bar magnet has a magnetic moment 1 25 Am The magnetic field at a distance 0 1m on its axis will be 1 1 2 x 10 4 T 3 2 5 104 T 2 2 5 10 T 4 1 2 x 104 T

bar magnet is cut into three equal parts questionndicular to its length and each part has magnetic moment M The magnetic moment of the bar magnet was 1 M 3 3M M 2 3 1 3 4 M 3

Aakash Institute 72 In a moving coil galvanometer identify the incorrect option 1 We obtain a non linear scale since ix tane 2 Increasing the number of turns increases the voltage sensitivity proportionally 3 The magnetic torque on the coil is proportional to cote where 0 is the deflection in the coil

Aakash Institute 60 The magnetic field at the point O in the given figure is 1 2 Ho 3 1 8 Hol 3 1 8 3 3 1 Hol 4xa 60 a 6 6

magnet is cut into three equal parts perpendicular to its length and each part has magnetic moment M The magnetic moment of the bar magnet was estion 1 M 3 3M M 2 3 4 M 3

A non conducting ring of radius r and mass m has a total charge q distributed uniformly on it The ring is rotated about its axis with angular speed Find the magnetic field at the centre 1 2 3 4 90 4 r 249 00 r 4 90 2zr 4 90

You may want to review Pages 788 Part A B 792 Find the magnetic field 6 75 cm from a long straight wire that carries a current of 7 88 A VO A O T

Two point charges q1 and q2 of 10 8 C and 10 8C are placed 0 1m apart C alculate electric field intensity at a B an d C Charges are kept on A and B ACD is an equilateral triangle of side 10cm AD extended upto point B such that AB 15cm

Moving Charges and Magnetism 53 The value of Magnetic field at the end of a very long solenoid carrying a current i will be n is the number of turns per unit length 1 Honi Ini 2 Honi 2

tic field with its 49 In a toroid the number of turns per unit length is 1 4x ampere The 1000 and current through it is magnetic field produced inside in Wb m is

2r heetquesti 65 A square of side 10 m is placed in a magnetic field of 0 2T The maximum torque on it when a current of 10 A is passed through it is 1 2 10 Nm 2 2 Nm 4 Zero 3 2 x 102 Nm LAX

Aakash Institute 44 The graph that depicts the variation of magnetic field 49 due to a circular loop of current placed with its centre at origin in x y plane 1 3 Z B i B Z 2 4 Z Z B O Z B v 50

9 CHO 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 2 2 4 4

Axis of solid cylinder of infinite length and radius R lies along y axis it carries a uniformly distributed current I along y direction Magnetic field at a point A B Hol 4 R HOI 2 R i k R 2 y R 2 is Correct Answer

A rod PQ of mass m length R 2 is hinged at P in a cylindrical magnetic field region or radius R with horizontal axis as shown The magnetic field is increasing at a rate of B T s If the rod is released from the initial position as shown The induced emf is found to be zero when end Q just enters the cylindrical region The magnetic field at that instant is 4p X X X X R X X P Initial position of rod X R 2 R X B R 6g X 1 2 value of p is m

speed in such a way that it passes through a circular loop of wire vertically below it S At the time t midpoint of the bar magnet passes through the circular loop Which of the following graphs best represents the time dependence of the induced current in the loop Here positive current means an anticlockwise current through the loop when the loop is viewed from above A B C D t N

Two wires A and B have lengths 40 cm and 30 cm A is bent into circle of radius R and B into an arc of radius R A current passes through A and 12 through B To have same magnetic induction at centre the value of 4 3 3 5 2 3 1 is

As the switch S is closed at t 0 the ring B is attracted towards A B 09 is repelled by A is initially repelled and then attracted is initially attracted and then repelled

Question No 11 Two conducting rings of radii r and 2r move in opposite directions with velocities 2v and v respectively on a conducting surface S There is a uniform magnetic field of magnitude B perpendicular to the plane of the rings The potential difference between the highest points of the two rings is 38 B

Magnetic field at point O of given current distribution Hol 4TR 4 k j 0 k 4R Attempt All 35 questions 24

A conductor AB of length L carrying current 2 is placed perpendicular to long straight conductor XY carrying current as shown in figure The force on wire AB in magnitude is X L 2 Hola 2 A 1 B In 2 2440 1 2 3x In 2 O In 3 Ho 1 2 Hol1 2 10 2

Force between two identical bar magnets whose centres are r m apart is 4 8 N when their axes are in the same line If separation is increased to 2r the force between them is reduced to 1 2 4 N 3 1 2 N 2 0 6 N 4 0 3 N A magnetic needle oscillates in a horizontal plane with a period T at a place where the angle of dip is 60 When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian its period will be 1 T 2 2 T 3 2 T 4 2T If mass is increased 4 times then the time period of a magnetometer when suspended in earth s magnetic field becomes 2 quadruple 1 double COLL IC

Aakash Institute 31 A charged particle of charge q and mass m moving along positive x direction with a velocity v enters a region where there is a uniform magnetic field B k from x 0 to x d The particle gets deflected through an angle 0 from its initial path The specific charge of the particle is 1 V cose Bd X 0 X x d 2 mv qB v sine Bd

27 A rectangular loop PQRS made from a uniform wire has length a and breadth b and mass m It is free to rotate about the arm PQ which is hinged about the horizontal axis y axis A uniform magnetic field Bi exists in the region If the loop remains in horizontal position in equilibrium then the magnitude of current in loop is PQ SR b SP QR a X mg 1 3B a mg 3 2B b S Z P Q R 2 4 gravity y mg 6B a mg 6B b

A rod of length 0 6 m rotates in the plane of the paper with an angular velocity of w 5 rad sec about a pivot at one end P A uniform magnetic field of strength 1 T exists perpendicular to the plane of rotation directed into the plane as shown The potential difference between the ends P and Q V V is X X X X X Q P A 0 9 V X B 0 9 V C 1 8 V D 1 8 V X X X X X X X X X Xp X X X X X X X X X

Aakash Institute 16 Figure shows a straight wire of length carrying a current i The magnitude of magnetic field produced by the current at point P is 1 2 Tl 2Hol P 2 Holl 4xl Hol

5 A ring of radius R with charge q uniformly distributed over it is rotated with angular speed around its axis Find magnetic field at the centre of the ring 1 3 H 90 2r Hq 4r 2 H q0 2Hr H90 4r

7 Two long straight wires of telephone circuit inside a house are coplanar with and run parallel to a third long straight conductor that carries a current i i sin t The conductor induced a noise in the telephone circuit The rms voltage per unit length of this induced noice is xx5 find x Express your answer in V Take d 2d A S 50rad s 73 In 2 THE

Figure shows cross sectional view of a long solid cylinder of radius R Current I flows along outward direction along length of cylinder Then find B dl along BA Given OB 3 1 R OA 2R ZOBA 45 Where O is point of axis of cylinder THE N GROUP 2 16 B B 6 D 0 12

Consider a set of six infinite long straight parallel wires arranged perpendicular o the plane of paper in a hexagon as shown The length of the each side of the hexagon is 3cm If the magnitude of the magnetic field at point Pis 5n 10 T then find n A 2A 2A A

Statement I For a current carrying long straight wire the magnetic field lines are with their centers on the wire Statement II Right hand thumb rule gives the direction of magnetic field due to carrying long straight wire A Both statement are true Statement II is the correct explanation of Statement I B Both statement are true Statement II is not correct explanation of Statement I C Statement I is true Statement II is false D Statement I is false Statement II is true

If an electric field is set up with points A and B What happens to the potential of an electron with an initial kinetic energy as it moves from point A to B What is the electrical potential energy

Which of the following is correct in Doppler s effect in one dimensional motion of source and observer A If source and observer are both moving with same velocity wavelength will remain same B If source is receding away from observer with constant acceleration starting from rest then apparent frequency will continuously decrease C If observer is receding away from source which is emitting sound since very long with constant acceleration starting from rest then apparent frequency will first decrease then increase and finally no frequency will be detected by observer D If observer is moving towards source with constant acceleration starting from rest then apparent frequency received by observer will continuously increase

A uniform ring of radius 1 meter carries current 0 4 A The ring is being rotated about its centre in horizontal plane with constant angular velocity T rad s A uniform magnetic field of magnitude 5 0 Tesla has been applied transverse to the plane of ring The linear mass density of ring is 1 kg m Find the tension developed in N in the ring TT X X X X X 0 4 A X X X X X 5 N O 4 N X X X X X X X X X X X X X X X X X X X X X X X X B 5 0 T X X X

We know when current i is passed through a thin circular coil the magnetic induction o n the axis of the coil at a distance x from th Moir 2 r x 3 2 e center is B Now magnetic induction at centre of coil m eans x becomes zero and B Hoi 2r QUESTION Now our college sir gave that to know the magnetic field on the circular coil x will be equal to r and field on the surface i Hoi Is it correct I am thinking we s 25 2r hould not do like that because x is the lengt h along the axis how can we take x r dista nce from centre to any point on the coil will be r But how can we take x r Can yo u please explain weather it is correct or wro ng And also i am thinking field on the coil must be zero according to oersted s experi s B

The flowmeter utilizes a magnet to apply a magnetic field B across an artery This field produces magnetic force F that cause the positive and negative ions in the blood to move to opposite sides of the artery The segregation of charges creates an electric field E within the artery The voltage V across the artery is measured by the meter shown in figure and is equal to Ed The electric field produces an electric force F on the ions that acts in the direction opposite to F Charges continue to accumulate until an equilibrium condition occurs when F F At equilibrium v V Bd where v is the velocity of flow of blood in the artery and d is the diameter of the artery Density of blood is 10 kg m m artery magnet magnet voltmeter Which of the following will occur when the magnet used in the flowmeter discussed in the passage is replaced with a stronger magnet A The electric field will reverse polarity B The electric field will decrease C The voltage will increase D Blood will flow faster

A particle of mass m has an electric charge q This particle is accelerated through a potential difference V and then entered normally in a uniform magnetic field B It performs a circular motion of radius R The ratio of its charge to the mass specific charge A 2V 22 B R B V 2BR VB 2R 9 m is D mV BR m is also called

2 A long wire PQR is bent at right angles at the point Q Fig 1 107 and 2 A current is flowing through it Deter mine the magnetic field at the point O on the extension of RQ when OQ 5 cm P 2A 5cm 4 x 10 6 TI

18 The magnetic field due to current carrying loop of radius 3cm at a point on the axis at a distance of 4 cm from the centre is 54u T Its value at the centre of the loop is O 125 T O 150 T 75 T O 250 T 2

magnetic field that is increasing at the constant rate of 10 0 mT s at what rate is 14a A long solenoid has diameter 12 0cm When a current I exists in its windings a uniform magnetic field of magnitude B 30 0 mT is produced in its interior By decreasing I the field is caused to decrease at the rate of 6 50 mT s Calculate the magnitude of the induced electric field a 2 20 cm and b 8 20 cm from the axis of the solenoid 11h A small loon of area 8 mm is placed inside a long solenoid that has 854 turns cm and carries a sinusoidally varying

3 A proton and an alpha particle having the same kinetic energy are allowed to pass through a uniform magnetic field perpendicular to their direction of motion Compare the radii of the paths of proton and alpha particle CBSE 2000

b A wire 50 0 cm long carries a 0 500 A current in the positive direction of an x axis through a magneti 3 3 00mT j 10 0mT k In unit vector notation what is the magnetic force on the wire