Magnetic Field due to current Questions and Answers

4 14 Two straight parallel conductors are spaced 50cm apart and carry oppositely directed currents the first 20A the second 24A A point P is separated from the first conductor by a distance of 40cm and from the second by 30cm Calculate the magnetic field of induction at P Ans 188 68 x 10 7T and a 32

4 mtG Objective NCERT P THE SOLENOID AND THE TOROID 55 A solenoid of length 0 6 m has a radius of 2 cm a is made up of 600 turns If it carries a current of 4 then the magnitude of the magnetic field inside solenoid is n 1 Moving Tw are dire for a 62

c d 1 2 x 10 5 N repulsive 5 A long straight wire carrying current of 30 A rests on a table Another wire AB of length 1 m mass 3 g carries the same current but in the opposite direction the wire AB is free to slide up and down The height upto which AB will rise is a 0 6 cm b 0 7 cm c 0 4 cm d 0 5 cm

56 A solenoid of length 50 cm having 100 turns carries a current of 2 5 A The magnetic field at one end the solenoid is a 3 14 x 10 T c 1 57 x 10 T b 6 28 x 10 T d 9 42 10 T h C Ol a c T

A current I 2A flows in a circuit having the shape of isosceles trapezium The ratio of the bases of the trapezium is 2 Find the magnetic induction B at symmetric point O in the plane of the trapezium The length of the smaller base of the trapezium is 100m and the distance r 50m I H 0

47 A4 A current carrying loop consists of three identical quarter circles of radius 5 cm lying in the positive quadrants of the x y y z and z x planes with their centres at the origin joined together value of B at the origin is a i j k T 10 c i j k T b j k T 10 d 10 i j k T 48 The electric current in a circular coil of two turns produced a magnetic induction of 0 2 T at its centre The coil is unwound and then rewound into a

A particle with a charge of 7 4 nC is moving in a uniform magnetic field of B 2 25 T K The magnetic force on the particle is measured to be F 4 02x 10 7N 1 7 4x10 7N a Calculate the x component of the velocity in m s of the particle b Calculate the y component of the velocity in m s of the particle

8 Two a particles have the ratio of their velocities as 3 2 on entering the field If they move in different circular paths then the ratio of the radii of their paths is a 2 3 b 3 2 c 9 4 d 4 9

the magnetic force on the wire is a 0 14 N b 0 24 N c 0 34 N d 0 44 N 12 The magnetic force per unit length on a wire carrying a current of 10 A and making an angle of 45 with the direction of a uniform magnetic field of 0 20 T is a 2 2 Nm b d 4 2 Nm Nm 1 c amlar coil of 20 turns and 10 cm radius is placed

c 4 x 10 5 N 14 A rectangular coil ABCD is hung from one side of a balance as shown in figure A 500 g mass is added to the other arm d 3 x 10 25 N 500 to balance the weight of the coil A current of 9 8 A is passed through the coil and a constant magnetic field of 0 4 T acting inward in xz plane is switched on such that only arm CD of length 1 5 cm lies in the field The additional mass m must be added to regain the balance is a 4g b 5 g c 6 g d 7 g 15 Which one of the following is correct statement 21

d any one of i ii and iii 0 Two particles of equal charges after being accelerated through the same potential difference enter in a uniform transverse magnetic field and describe circular paths of radii R and R Then the ratio of their respective masses M M is a R R b R R c R R d R R

A circular coil 0 0500 m in radius with 30 turns of wire lies in a horizontal plane It carries a counterclockwise as viewed from above current of 5 00 A The coil is in a uniform 1 20 T magnetic field directed toward the right Find the magnitudes of the magnetic moment and the torque on the coil

2 A charged particle with charge q enters a region of constant uniform and mutually orthogonal fields E and B with a velocity perpendicular to both E and B and comes out without any change in its magnitude or direction Then a v BxE E b v ExB B c V BxE B d v ExB E

a 30 b 45 c 60 d 90 D The horizontal component of earth s magnetic field at a certain place is 3 0 x 10 5 T and having a direction from the geographic south to geographic north The force per unit length on a very long straight conductor carrying a steady current of 1 2 A in east to west direction is a 3 0 x 10 5 Nm c 3 6 x 10 5 Nm b 3 2 x 10 N m l d 3 8 x 10 5 Nm

13 A circular coil of 20 turns and 10 cm radius is placed in a uniform magnetic field of 0 10 T normal to the plane of the coil If the current in the coil is 5 A cross sectional area is 105 m and coil is made up of copper wire having free electron density about 10 m then the average force on each electron in the coil due to magnetic field is a 2 5 x 10 5 N c 4 x 10 25 N b 5 x 10 25 N d 3 x 10 25 N

A 2 5 m long straight wire having mass of 500 g is suspended in mid air by a uniform horizontal magnetic field B If a current of 4 A is passing through the wire then the magnitude of the field is Take g 10 m s a 0 5T b 0 6 T c 0 25 T d 0 8 T of the 9 8 A magr is sw 15 cm be ad a

An electron beam is retarding in same plane of coil X coil Y as shown in figure Direction of induced currents in coil X coil Y respectively will b Coil X O Clockwise Anticlockwise Anticlockwise Clockwise O Clockwise Clockwise Anticlockwise Anticlockwise 4 e beam retarding Coil Y Marks 4

A current of 10 A is flowing in a wire of length 1 5 m A force of 15 N acts on it when it is placed in a uniform magnetic field of 2 T The angle between the magnetic field and the direction of the current is a 30 b 45 c 60 d 90 D The horizontal component of earth s magnetic 15 W ab a b c d

Which one of the following is not correct about Lorentz Force a In presence of electric field E r and magnetic field B r the force on a moving electric charge is F ql r vx B r b The force due to magnetic field on a negative charge is opposite to that on a positive charge c The force due to magnetic field become zero if velocity and magnetic field are parallel or anti parallel d For a static charge the magnetic force is maximum

6 A straight wire having mass of 1 2 kg and length 1 m carries a current of 5 A If the wire is suspended in mid air by a uniform horizontal magnetic fie then the magnitude of field is a 0 65 T b 1 53 T c 2 4 T d 3 2T 7 A circular loop of radius R carring of ca 10 the c a c 14 Are is h

36 A loop shown in the figure is immersed in the varying magnetic field B Bot directed into the page If the total resistance of the loop is R then the direction and magnitude of induced current in the inner circle is Bo na 6 a clockwise b anti clockwise c clockwise R 2 B ra 46 R Bon a 6 R d clockwise Bo 46 na R b 12

14 Electric charge q is distributed uniformly over a rod of length 1 The rod is placed parallel to a long wire carrying a current i The separation between the rod and the wire is a The force needed to move the rod along its length with a uniform velocity vis Maiqu a 19 2na Hoiqul ifat 2 a c Moiqu b Ara FqVB d Hoiqul 4

88 Resistances P Q S and R are arranged in a cyclic order to form a balanced Wheatstone s network The ratio of power consumed in the branches P Q and R S is a 1 1 b R P c P Q d P R

Four wires each of length 2 0 m are bent in four loop P Q R and S then suspended in uniform magnet field All loop carries equal currents which statement of the following is true 1 Couple acting on the loop P is greatest 2 Couple acting on the loop Q is greatest 3 Couple acting on the loop R is greatest 4 Couple acting on the loop S is greatest D pro Q R P

O O Sp 3 A large frictionless disk can rotate about its central vertical axis in a uniform static magnetic field of induction B pointing vertically upward A particle P of mass m and charge q is connected with the help of an inextensible thread of length 1 to a nail O fixed at a distance r l r from the centre C of the disk as shown in the top view of the situation The disk is rotated at various constant angular velocities Draw graph between tension force T in the thread when the particle stops relative to the disk and corresponding angular velocity of the disk T mw qwB x 1 193 W AND T 9WB mc 0 1 0 w 9B m ingulating frame is rotating in

Keeping current per unit length of arc constant the variation of magnetic field at the centre of an arc B with the angle subtended by the arc at the centre 0 can be best represented by Jon of it BA 1 3 2 0 BA 2 4 BA B 0 00 9 0 0

A long straight wire carrying current of 30 A rests on a table Another wire AB of length 1 m mass 3 g carries the same current but in the opposite direction the wire AB is free to slide up and down The height upto which AB will rise is a 0 6 cm c 0 4 cm b 0 7 cm d 0 5 cm

A magnet magne noment ZUK mz is placed along the z axis in a magnetic field B 0 4j 0 5k T The torque acting on the magnet is A 8j N m B 6j N m C 8i N m D 6j N m Your Answer A

27 A short magnet oscillates in vibration magneto meter with a frequency 10Hz where horizontal component of earth s magnetic field is 12 T A downward current of 15A is established in the vertical wire placed 20cm west of the magnet New frequency is 2 M B B 2 2 5Hz 4 5Hz I 1 4Hz B 10 21 4r a 3 9Hz B 15PT

A plane electromagnetic wave travels in vacuum along z direction What can you say about the directions of its electric and magnetic field vectors If the frequency of the wave is 30 MHz what is its wavelength

5 A charged ball B hangs from a silk thread S which makes an angle P with a large charged conducting sheet P as shown in the figure The surface charge density of the sheet is proportional to a cos b cot 8 c sin 0 d tan 0 B

25 A magnetic needle of pole strength 20 3 Am is pivoted at its centre Its N pole is pulled eastward by a string The horizontal force required to produce a deflection of 30 from magnetic meridian take B 10 T is 1 4 10 N 3 127 133 3 10 N 2 2 10 N 4 4 3x10 N

FIELD 73 An electric dipole is placed at an angle of 30 with an electric field of intensity 2 x 10 NC It experiences a torque equal to 4 N m The charge on the dipole if the dipole length is 2 cm is a 8 mC b 4 mC c 6 mC d 2 mC

he drawing shows four insulated wires overlapping one another forming a square with 0 050 m sides All four wires are much longer than the sides of the square The net magnetic field at the enter of the square is 74 T directed into the drawing Calculate the current I 3 6 A 3 8 A 7 1 A

1 lc Which of the following statement is false for the properties of electromagnetic waves 1 These waves do not require any material medium for propagation 2 Both electric and magnetic field vectors attain the maxima and minima at the same place and same time 3 The energy in electromagnetic wave is divided equally between electric and magnetic vectors 1 Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave

4 4 A conducting rod AC of length 4 is rotated about a point O in uniform magnetic field B directed into the paper AO 1 and OC 31 Then X X X x xx xAx x x0x x x fuqvB X X X x X xx x X X X X X

Two circular coils X and Y having equal number of turns carry equal currents in the same sence and subtend same solid angle at point O If the smaller coil X is midway between O and Y and If we represent the magnetic induction due to bigger coil Y at O as By and that due to smaller coil X at O as Bx then 2r d 2

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

An electric current passes through a long straight wire At a distance 5 cm from the wire the magnetic field is B The Field at 20 cm from the wire would be 1 2B 2 B 4 3 B 2 4 B

15 Two long parallel wires are separated by a distance of 2 m They carry a current of 1A each in opposite direction The magnetic induction at the midpoint of a straight line connecting these two wires is out boazi al A8 0 1 zero 2 2 10 7 T 213 4 10 T 4 4 10 T

Two long straight conductors are held parallel to each other 7cm apart The conductors carry currents of 9A and 16A in opposite directions The distance of neutral point from the conductor carrying 16A current is 1 9cm 2 16cm 3 25cm 4 63 25cm

2 A long straight wire carries an electric current of 2A The magnetic induction at a perpendic distance of 5 m from the wire is 4 x 10 7 Hm 3 12 10 8 T 1 4 108 T X 2 8 10 8 T X 4 16 10 T 1 i 24 The in numb

1 5 T north 2 10 T north 3 l TOUDUT A current of 5 A is flowing through a long straight copper wire The ratio of the magnetic induction at distances of 1 0 cm and 2 0 cm from the wire is 21 If 1 1 2 2 1 4 3 2 1 4 4 1 ulut noble contains 7 strands of wire each carrying a current of 5 A The magne 22

A conducting wire in the shape of Y with each side of length is moving in a uniform magnetic field B with a uniform speed v as shown in the figure The induced emf at the two ends X and Y of the wire will be X X B Q X X X P X X 0 X X X

35 A triangular current carrying wire loop with current i is placed in a uniform and transverse magnetic field as shown in the figure X A 30 120 1 F 3 X X X xB 30 D ne agis If the magnetic force on the sides AC CD and DA respectively have a magnitude of F F2 and F3 then 2 F and F have an angle of 120 between them 3 F 3 F 4 All of these

wo long parallel wires carry currents of I 2 95 A and I 4 75 A in the directions indicated in the figure below where d 23 5 cm Take the positive x direction to be to the right P a Find the magnitude and direction of the magnetic field at a point midway between the wires magnitude T direction counterclockwise from the x axis b Find the magnitude and direction of the magnetic field at point P located d 23 5 cm above the wire carrying the 4 75 A current magnitude MT direction counterclockwise from the x axis

Copper disc of radius 10 cm is rotating in magnetic field B 0 4 gauss with 10 rev sec What will be potential difference across peripheral points of disc 1 20 uV 3 zero 2 10 uV 4 5muV

A cell is connected between two points of a uniformly thick circular conductor as shown in figure Magnetic field at the centre of the loop due to the circular conductor will be 1 zero 3 Ho V in in 2 4 Ho 1 1 2a Mo i in

A long solenoid of radius R carries a time t dependent current I t L 1 t A ring of radius 2R is placed coaxially near its middle During the time interval 0 t 1 the induced current 1 and the induced EMF V in the ring change as 1 At t 0 5 direction of I reverses and V is zero 2 Direction of I remains unchanged and VR is zero at t 0 25 3 Direction of Ip remains unchanged and VR is maximum at t 0 5 4 At t 0 25 direction of Ip reverses and VR

A wire carrying current I has the shape as shown in adjoining figure Linear parts of the wire are very long and parallel to X axis while semicircular portion of radius R is lying in Y Z plane Magnetic field at 10 point O is I 4 R 1 B Ho i 2k 2 B Ho 2k 4T R I 3 B Ho ri 2k 4T R 4 B No 2k 4T R X R Z O