Magnetic Field Questions and Answers

A charge q and mass m moving with velocity venters a region of uniform magnetic field B at an angle 8 Which of the following represents correct graph for pitch w r t angle 8 0 0 90 OP OP O O View In English 0

Why amperes law is not valid for cir cular current carrying coil Ampere s Law is a simple tool for evaluating electrically induced magnetic field at a point For Ampere s Law to be applicable the magnetic field should be in a pattern which creates an Amperian Loop Amperian loop should have the magnetic field strength tangential to the loop or normal to the loop created by the magnetic field around it This loop should also have a non zero or a uniform magnetic field in order to be applicable to Amperian Circuital Law In case of a closed circular loop the magnetic field induced due to the current flowing across the loop does not create such an Amperian loop This is the reason why ampere circuital law cannot be used in circular closed loop although circular loop has symmetrical stucture as the conditions for creating an amperian lo pattern of the induced magnetic field is not satisfied

In the given figure the centre of a small conducting circular loop B lies on the axis of bigger circular loop A and their axis are mutually perpendicular An anticlockwis when viewed from the side of B current in the loop A start increasing then D A current induced in the loop B is in clockwise direction when viewed from above the B B current induced in the loop B is in anti clockwise direction when viewed from above the B O current must induced in the loop B but its direction can not be predicted no current is induced in the loop B

71 Consider a region inside which there are various types of charges but the total charge is zero At points outside the region a the electric field is necessarily zero b the electric field is due to the dipole moment of the charge distribution only c the dominant electric field is inversely proportional to r for larger distance from origin d the work done to move a charged particle along a closed path away from the region will not be zero and are 2 Two fom kanges or I he did in these a distance of 10 print Pisa dilance of on the peri endilar are 2

A moving coil galvanometer has 50 turns and each tum has an area 2 x 10 m The magnetic field produced by the magnet inside the galvanometer is 0 02 T The torsional constant of the suspension wire is 10 N m rad When a current flow through the galvanometer a full scale deflection occurs if the coil rotates by 0 2 rad The resistance of the coil of the galvanometer is 50 2 This galvanometer is to be converted into ammeter capable of measuring current in the range 0 1 0 A For this purpose a shunt resistance is to be added in parallel to the galvanometer The value of this shunt resistance in ohms is 50

A positively charged particle with a charge q enters a region in which there is a uniformelectric field E and a uniform magnetic field B both directd parallel to the positive y axis At t 0 the particle is at the origin and has a specd directed along the positive x axis The orbit of the particle projected on the x z plane is a PO circle Let T be the time taken to complete one revolution of this circle The y coordinate of the particle at T is given by mE 2 8 b 2n inE R m vm aR aR 2 mv aR

Ans 2 15 A long solenoid of 50 cm length having 100 turns carries a current of 2 5 A The magnetic field at the centre of the solenoid is Ho 4 x 107 Tm A 1 3 14 x 10 5 T 2 6 28 x 10 4 T 3 3 14 x 10 4 T 4 6 28 x 10 5 T Ans 2

Weight of magnesium atomic mass 24 u deposited by a quantity of electricity which displaces 11200 mL of Cl gas at STP will be O 6g O 9 g O 12 g 24 g Asked by 2140569 aesl id Standard XII Stream NEET Aug 2 2021 at 2 22 PM Add your responses Type Text

25 In a guitar two strings A and B made of same material are slightly out of tune and produce beats of frequency 6 Hz When tension in B is slightly decreased the beat frequency increases to 7 Hz If the frequency of A is 530 Hz the original frequency of B will be 1 537 Hz 3 524 Hz Ans 3 2 523 Hz 4 536 Hz

In a toroid the number of turns in per metre length is 500 1 and current through it is A The magnetic field produced 2 inside in weber m will be 10 10 4 2 x 10 2 5 x 10 3

In Fig there is a frame consisting of two square loops having resistors and inductors as shown This frame is placed in a uniform but time varying magnetic field in such a way that one of the loops is placed in crossed magentic field and the other is placed in dot magnetic field Both magnetic fields are perpendicular to the planes of the loops If the magnetic field is given by B 20 10t Wbm 2 in both regions 1 20cm b 10cm and R 100 L 10H The direction of induced current in the bigger loop will be 1 20 cm X X L X R PRING X X X R www elle b 10 cm

Example A current I flows in the anticlockwise direction through a square loop of side a lying in the xoyp with its center at the origin Find the magnetic induction at the center of the square loop

The magnetic force on a current carrying wire of length placed in a magnetic field as shown in the figure is B A Bil Bil Bil 2 T B

A particle of charge 2 C is at rest in a magnetic field B 3K T Magnetic lorentz force on the charge particle with respect to an observer moving with velocity V 4 m s will be 12x10 N O 24x10 8 N O 6x10 KN

An electron and a proton enter a magnetic field perpendicularly Both have the same kinetic energy Which o the following is true O Trajectory of proton is less curved Trajectory of electron is less curved Both trajectories are equally curved Both move on a straight line path

Uniform magnetic field B exists in circular region asrs2a A charge particle q m is projected from a 0 with velocity v Maximum value of v so that particle does not exit the magnetic field region is 2 Options 4 08 0 3 m 08 0 X900 5 q8 a

46 A wire is wound on a long rod of material of relative permeability p 4000 to make a solenoid If the current through the wire is 5A and number of turns per unit length is 1000 per metre then the magnetic field inside the solenoid is an tesla Find the value of a

A uniform magnetic field exists in a region is given by B 4RT A square loop of edge 10 cm and carrying current of 5 A is placed with its edges parallel to x and y axes The net magnetic force experienced by loop is 10 cm 0 b SA OB 10 cm 8 O 0 6 N O 0 4 N O Zero

and radius r is rotating with an angular velocity on a rough horizontal plane A uniform and constant magnetic field B is applied perpendicular and into the plane An inductor L and an external resistance R are connected through a switch S between centre of the disc O and point P The point P always touches the circumference of the disc Initially the switch S is open Take coeffi cient of friction between the plane and disc as u Assuming the disc has no resistance P B L vorrors A The induced emf across the terminals of the switch is Bor2 when disc has angular speed B The switch is closed at t 0 the torque re quired about the centre of the disc is 1 4 B r mgr 4 S to maintain the constant angular speed wat steady state C The current in the circuit as a function of time will be given as Br w 2R R 1 eL when disc has a constant angular speed w D The switch is closed at t 0 the torque required 3 3 umar to maintain the con

Five long wires A B C D E each carrying current lo are placed on the vertices of a regular hexagon of side a as shown Each wire carries current out of plane of paper Resultant magnetic field at centre O is along A O B O Positive x axis O Negative x axis Positive y axis O Negative y axis X

A negative charge d moves parallel to a very long straight wire carrying current as shown in figure The direction of force on the charge is y O Opposite to OX Along OX Opposite to OY X

11 A charged particle of charge q and mass moving with velocity vo along positive x axis a shown in the figure enters in a uniform magneti field Bo directed along negative z direction Th time spent by particle inside the magnetic fiel will be q m 1 3 2 m 3qBo AM qBo 30 X x X Hi XXX Bo X X 2 4 X X X X X x Am 3qBo 3 m 2qBo ex extends upto large distance X

A freely suspended magnet oscillates with period T in earth s horizontal magnetic field When the bar magnet is brought near it such that magnetic field created by bar magnet is in same direction as earth s horizontal magnetic field the period decreases to T 2 The ratio of the field of the magnet B to the earth s magnetic field BH 1 1 3 2 1 1 3 3 1 4 9 1

A current carrying loop of radius r carries a current in clock wise direction It is placed in a uniform magnetic field B such that plane of the coil is parallel to field The net torque on the coil is O r lB 2 r IB 2 rlB Zero

SKAR PHYSICS FULL SYLLABUS The value of energy density in an electromagnetic wave is 50 aa 1 E 3 E 2 E 280 1 1 0 3 E E 200 4 0E

For given arrangement in horizontal plane the possible direction of magnetic field r Induced current 1 towards right 3 vertically upward V 2 towards left 4 vertically downward tating about its

0 A particle of charge q mass m moving with velocity vo i 1 enters a region of uniform magnetic field Bi Find displacement of particle after time t 1 3 mvo i 2k qB 2 mvoi qB 2 Aak mvo Found ational Services Limited qB

Two loops carrying current in opposite sense placed parallel to each other are moved closer to each other Then the current 00 1 In both of them increases 2 In both of them decreases 3 Increases in one and decreases in other 4 In both of them remains same

Ionized hydrogen atoms and a particles with same kinetic energy enters perpendicular to a constant magnetic field B The ratio of the radii of path followed by hydrogen atom to a particle is 1 Point 1 4 1 1 2 1 1 2

9 Two parallel wires carry the a current I in the same direction Midway between these wires is a third wire also parallel to the other two which carries a current 0 5 I but in the direction opposite from the first two wires In which direction are the net forces on the outer wires A Both forces on the two wires are in the same direction in space O B Since the net forces are zero there is no direction O c Both forces are toward the centre wire O D Both forces are away from the centre wire

Example 5 Figure 4 12 shows two current carrying wires 1 and 2 Find the magnitudes and directions of the magnetic field at points P Q and R 20 cm P 20 AA 30 A 10 cm 10 cm 10 cm 10 cm O R

Antiparallel currents are directed so that one is our of the page and the other is into the page The magnetic field is B at any point equidistant from the wires and the field is B at that point due to on wire alone then 1 B B for all equidistant points 2 B B for all equidistant points B B for close equidistant points only B B for close equidistant points only 3 4

A negative charge q moves parallel to a very long straigh wire carrying current I as shown in figure The direction of force on the charge is y q Opposite to OX Along OX O Opposite to OY Along OY X

In this experiment a student plotted a graph tan 0 versus I mA as shown in the figure Ho 4 x 10 7 T m A Answer the following question If the horizontal earth magnetic field is 0 6 10 4T and the number of turns N is 200 find the radius of the coil R that is used in this experiment tan 0 Slope 0 02 I MA m 1 5 O m 2 5 O

A conducting rod of length 1 m negligible resistance slides without friction on two parallel vertical conducting rails connected at the top through a resistor of resistance R The rails are also of negligible resistance A uniform magnetic field Bo exists perpendicular to the plane of the rails pointing inward After a long time the heat dissipated in the resistor per second is 1 m g 2B 2R 2m g R www R B 2 f ilksi 98 filb m g R B 1 m g

20 The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the center is 54 T What will be its value at the center of the loop a 125 T b 75 T c 250 T O d 150 T

18 A long straight wire of radius a carries a steady current I Current is uniformly distributed over cross section The ratio of magnetic fields of B B at radial distances a 2 2 a respectively from the axis of wire is a 1 Ob 4 Oc 1 4 d 1 2

Knowledge Sections Q No 22 Optical square is A Engineer s square having stock and blade set at 900 B A constant deviation prism having the angle of deviation between the incident ray and reflected ray equal to 90 C A constant deviation prism having the angle of deviation between the incident ray and reflected ray equal to 45 D Used to produce interference fringes 7

A long cable is constructed of a solid conductor of radius r in a co axial hollow cylindrical conductor inner and outer radii R and R respectively Io current flows in both the conductors in opposite directions The magnetic field B at a distance x from the axis of the cable is Answer A B C D Your Attempt B B B olo 2 X Holo 2 T Correct answer when r x R when x r Holo R2 x 2 x R R when R x R2 B 0 when x R Rate this quest

Magnetic induction as a function of distance from the axis of a radially symmetrical parallel stream of electrons is B ar where a is a constant The expression for current density as a function of ris O ar the 2ar the

A conducting wire of parabolic shape initially y x is moving with velocity V Vi in a non uniform magnetic field 8 2 1 2 B Bo k as shown in figure If Vo Bo L and B C A BVL for B 0 2 L 4 D A BVL for B 2 are positive constants and A is the potential difference developed between the ends of the wire then the correct statement s is are A JA is proportional to the length of the wire projected on the y axis B A remains the same if the parabolic wire is replaced by a straight wire y x initially of length 2 L OB 0 V vi L e X 2019 R

Sir direction of magnetic field is not given How to find it plz explain in details Ae 22 A short current carrying conductor is placed perpendicular to the axis of a current carrying ring as shown The direction of force acting of the conductor is y axis Z axis x axis 1 Along positive x axis 2 Along negative y axis 4 Along negative z axis 3 Along positive z axis Aakash Educational Services Limited Regd Office Aakash Tower 8 Pusa Road New Delhi 110005 Ph 011 47623456

A square loop of side 10 cm is placed vertically in the East West plane A uniform magnetic field of 0 10 T is set up across the plane in North East direction The magnetic field is decreased to zero in 0 70 second at a steady rate The magnitude of induce emf during this time interval are A B 2 mV 1 mV C Zero

17 An electron proton have equal kinetic energies They enter magnetic field perpendicularly Then O a Both will follow different path with circular radii Ob Both will follow helical path O c Both will follow parabolic path d Both will move undeflected

In the diagram there are four conducting plates A B C and D placed parallel to each other at equal separation L If plate C starts moving towards plate B with velocity v Find the current in mA flowing in the wire connecting A and D assume all other plates to be fixed Given q2 2 C q 3 C v Q 91 91 B 92 92 93 93 0 C D

A coil having effective area A is held with its plane normal to a magnetic field of induction B The magnetic induction is quickly reduced to 25 of its initial value in 2 s Then e m f induced across the coil will be 4 C 3AB 8 AB 4 B D MH CET 2014 3AB 4 AB 2

A long wire carrying a steady current I lies in the plane of circular conducting loop placed at a certain distance from the wire There will be an induced current in the loop if it is ONO moved parallel to the wire roatated about an axis perpendicular to the plane of the loop passing through the centre of the loop rotated about an axis parallel to the wire passing through the centre of the loop

The periphery of an insulating disc of radius R and mass M is charged uniformly and has linear charge density A The disc is rotating freely with constam angular velocity about a vertical axis as shown Uniform magnetic field B extends over entire circular region of disc pointing downward If the magnetic field is switched off then find the value c B for which the disc stops 1 2 40 M TAR 200 M R 0 M AR o B

Magnetic induction as a function of distance r from the axis of a radially symmetrical parallel stream of electrons is B ar where a is a constant The expression for current density as a function of ris O O ar Ho 2ar Ho 3 ar Ho

2 An electron gun electron is accelarted through 320 volt on emerging from gun the electron been enters a uniform B 6x104 tesla perpendicular to speed If mass of electron is 9 0 x10 31 kg Find Electric field to neutralise deflection of electron produced by magnetic field Ans E 6 4x10 v m