Magnetic Field Questions and Answers

A solenoid of diameter 0 2 m has 500 turns per metre At the centre of this solenoid a coil of 100 turns is wrapped closely around it If the current in solenoid changes from zero to 2 A in 1 millisecond Induced emf developed in the coil is nearly O 2 45 V 3 95 V 6 55 V

6 As shown in figure A and B are two coaxial conducting loops separated by some distance When the switch S is closed a clockwise current flows in A as seen by O and an induced current flows in B The switch remains closed for a long time When S is opened a current 2 flows in B Then the directions of I and 12 as seen by O are 1 Respectively clockwise and anticlockwise 2 Both clockwise 3 Both anticlockwise 4 Respectively anticlockwise and clockwise B D

An infinite long straight wire is bent into the shape as shown in figure It carries current i and radius of circular loop is a The magnetic field at the centre of loop is d a Hol 2 a a Ho 1 i 2 a Hol 1 2 a

42 A conductor of length 34 carrying a curr placed perpendicular to a long straight conductor AB carrying current 27 as shown in the figure A B The magnitude of force acting on AB is 1 Ho2 In 4 4x 2 Ho 4 In 2 8K 3 H0 In2 2x A 201 10

The universal property of all magnetic substances is Diamagnetism Paramagnetism Ferromagnetism Non magnetism

A long circular tube of length 10 m and radius 0 3 m carries a current I along its curved surface as shown A wire loop of resistance 0 005 ohm and of radius 0 1 mis placed inside the tube with its axis coinciding with the axis of the tube The current varies as I I cos 300 t where I is constant If the magnetic moment of the loop is N I sin 300 t then N is JEE 2011 f o I

Two long parallel copper wires carry currents of 5A each in opposite directions If the wires are separated by a distance of 0 5m then the force per unit length between the two wires is Question Type Single Correct Type 1 2 3 4 10 5 N m attractive 10 5 N m repulsive 2 x 10 5 N m attractive 2 x 10 5 N m repulsive

of radius R carrying current I is placed in a magnetic field as shown in the figure On right hand side of yy the magnetic field is 2B outward and on the left hand side it is B inward as shown The magnetic force experience by the wire is Bo 1 2 BIR 2B 2 5 BIR

Two concentric circular loops of radii and 1 N 14 cm are placed in the Y Z plane as shown in the figure The magnetic moment of this loop system is NE Z 55 x 10 3 Am 55 x 10 3 Am 33 x 10 Am 33 x 10 3 Am 10 A 5A cm

A long solenoid carrying a current of 2 0 A has 1000 turns per metre If magnetic field inside the solenoid is 8 10 KT then find k Answer 1 9 0 8 2 3 4 5 6 7 3 4 5 6 7 0 1 2 3

3 54 A long cylindrical of radius R has a single layer of a conducting coil of wire wound on its circumference with no gap between two adjacent turns Diameter of cross section of the wire used is d d R If the breaking stress of the material of the wire is Ob then the magnitude of the direct current through the wire at which the coil will burst is nd where n is a positive integer Find the value of n nu R

Answer A B Your Attempt C Correct answer the magnetic field at a point on axis is zero the electric field on axis of cylinder is zero C The magnetic field outside the conductor is zero The electric field outside the conductor is zero Rate this

A uniformly distributed current flows in a long curved sheet along z axis with cross section having the form of a circular arc of radius R centred at O as shown If a long current carrying straight wire having current along z axis then magnetic force on length A of this wire at point O will be O 1 1 R E N T 2 HolloA 2 1 T R vy X R 2 Hol 4 2 7 T R

fa ya gradu arui ha tal Options Stationary Change FR O Moving Change O Accelerated Change Ra O None of these

A positively charged particle of charge Q and mass m is imparted velocity V from origin in region of uniform magnetic field of intensity of uniform B Bok Where Bo is positive constant Assume gravity free region At t 0 the particle is at origin List I 1 II III The radius of curvature is k is 3QBo The Kinetic energy of particle is value of k is The x co ordinate of particle is value of k is IV The angle made by velocity with positive y axis is cos The value of k is O I P OIR 114Q k 4 11 S kmvo QB III S the value of III T mv 0 k mv k 2QB 1 IV U The velocity of particle of origin is vol Then which of the following is correct match at t zm IV U The The List Il p 1 Q 2 R 3 S 4 T 8 U 12

ving Charges and Magnetism 119 2 and 3 carry current as shown Also shown are two points in the region A and B Choose the incorrect alternative B A 1 Magnetic field due to element 3 at A and B are in opposite directions 2 Magnetic fields due to elements 1 and 2 at points A and B respectively are in same direction 3 Magnetic field due to element 1 at B is directed along positive z axis 4 Magnetic field due to element 3 at any point on z axis is zero

Q 28 A charge particle of charge q and mass m is projected in a region which contains electric and magnetic field as shown in figure with velocity V at an angle 45 with x direction GE If V then net deviation in particle m motion will be neglect the effect of gravity in clockwise direction approx y V 45 0 5 OB mV 2qB 2 X 1

and y muced emf appear across the ends of having inductances L and are connected 1 in series i in parallel What is their equivalent 414L 39 If resistances R in circuit a of the figure shown is decreased what will be the direction of induced current in circuit b a 40 In the figure P and S are two coils What shall be after the quite b

Choose the correct option The magnetic field inside a long straight solenoid carrying current a b c d is zero decreases as we move towards its end increases as we move towards its end is the same at all points 13 3 FORCE ON A CURRENT CARRYING C IN A MAGNETIC FIELD We have learnt that an electric current flowing throu produces a magnetic field The field so produced exer magnet placed in the vicinity of the conductor French Marie Ampere 1775 1836 suggested that the magnet an equal and opposite force on the current carrying cond due to a magnetic field acting on a current carrying com demonstrated through the following activity ctivity 13 7 ke a small aluminium rod AB of about 5 cm Using o connecting wires suspend it horizontally from a and as shown in Fig 13 12 ace a strong horse shoe magnet in such a way that e rod lies between the two poles with the magnetic ld directed upwards For this put the north pole of e magnet vertically below and south pole vertically pove the aluminium rod Fig 13 12 onnect the aluminium rod in series with a battery key and a rheostat ow pass a current through the aluminium rod from ad A ned that the rod is

The variation of the intensity of magnetisation with respect to the magnetising field H in a diamagnetic substance is described by the graph in figure B O OA D O OB O oc OD A H

A point charge Q is placed just outside an imaginary hemispherical surface of radius R as shown in the figure Which of the following statements is are correct Q R A The electric flux passing through the curved surface of the hemisphere is 2 1 Q B Total flux through the curved and the flat surfaces is 0 C The component of the electric field normal to the flat surface is constant over the surface D The circumference of the flat surface is an equipotential

1 Magnetic flux Faraday s law Lenz s law A conducting ring is placed in a uniform magnetic field with its plane perpendicular to the field An emf is induced in the ring if it is B 1 rotated about its axis 2 translated 3 rotated about its diameter OL

In a cartesian system vector magnetic potential at a point x y z is defined as A 4x yax 2y2xay 3xyzaz The magnetic flux density at point 0 1 0 will be 2az 3ax 3ay 2az 2az

is a negative mark In a compound microscope the magnification produced by objective is 5 If the final image is obtained at the least distance of distinct vision and power of its eye piece is 20 D then the magnifying power of this microscope will be 1 80 3 100 2 50 4 30

imendian period of oscillation of dip needle is T When plane of a dip circle is along magnetic When plane of dip circle is perpendicular to the magnetic meridian the period of oscillation is T then is Angle of dip 30 91 1 2 3 2 2 1 4 1 14

A long straight wire placed along az axis carries a current of I 6 A in the az direction The magnetic flux density at a distance r 5cm from the wire will 22 10 6 wb m O 16 10 6 wb m 08 10 6 wb m 24 10 6 wb m

Figure shows an electromagnetic gun A bar of mass m resistance R and length L is free to slide on two smooth rails separated by a distance L A uniform magnetic field B is present perpendicular to the plane of the figure A capacitor of capacitance C is charged using a battery of emf Vo by placing switch S at 1 To fire the gun i e to impart a kinetic energy to the rod the switch is shifted to position 2 after the capacitor is fully charged The rails end abruptly at the point where the speed of the rod becomes maximum The efficiency of the gun can be defined as the kinetic energy imparted to the bar divided by the energy spent by the battery while charging the capacitor Calculate the efficiency of the gun Neglect self Vo 12 C X L R X X two

Key is in position 2 for time t Therea position 1 Resistances of the bulb and inductance of inductor are marked in the figure choose the correct alternative Bulb 1 R Key 12 Bulb 2 OR 1 Bulb 2 dies as soon as key is switched into position 1 2 Time in which brightness of bulb 1 becomes half its maximum brightness does not depend on t 3 If t total heat produced in bulb 1 is LE2 2R 2 4 Ratio of maximum power consumption of bulb

If a charged particle at rest experiences no electromagnetic force estion Type Single Correct Type 1 The electric field must be zero 2 3 The magnetic field must be zero The electric field may or may not be zero F

5 A particle of charge q and velocity v passes undeflected through a space with non zero electric field E and magnetic field B The undeflecting conditions will hold if a signs of both q and E are reversed b signs of both q and B are reversed c both B and E are changed in magnitude but keeping the product of B and E fixed d both B and E are doubled in magnitude

4 12 ms 18 A current carrying square loop is placed near a long straight 18 current carrying conductor in same horizontal plane as shown Then the loop will experience 1 a net torque acting upward perpendicular to the hori zontal plane 2 a net torque acting downward normal to the horizontal plane 3 a net attractive force towards the conductor 4 a not requiriva force away from the conductor 4 12 ms aurem gu ferager and are n at 1 2 Afri amy 3 4 from zufrit uforiam

5 5 car 5 53 Two long parallel wire of zero resistance are connected to each other by a battery of 1 0V The separation between the wires is 0 5m Ametallic bar which is perpendicular to the wires and of resistance 102 moves on these wires when magnetic field of 0 02T is acting perpendicular to the plane containing the bar and the wires Find the steady state velocity of the bar If the mass of the bar is 0 002kg find its velocity as a function of time Ans 100m s 100 1 e 1200 m s inc re a C

22 Current flows due north in horizontal transmission line Magnetic field at P vertically above it is directed P a North wards b South wards c East wards d West wards

16 A charged particle moving in magnetic field experience the force in a direction of the magnetic field b opposite to the direction of the magnetic field c perpendicular to the direction of magnetic field and velocity d none of these

line carries current from wes to east Then the direction o the magnetic field 2 m above it is west to east south to north north to south None of these Frect answer

21 The magnetic lines of force inside a bar magnet a Do not exist b depends on area of cross section of bar magnet c are from N pole to S pole of the magnet d Are from S pole to N Pole

Consider an annular region of inner radius a and outer radius 2a confining magnetic field within its boundary as shown A charged particle q m is projected radially as shown from inner boundary in magnetic field varying with kr radial distance as B B 1 K where Bo and are constants If charged particle exits out from region radially then flux of magnetic field through region is nakBoa Find the value of n a VO X Answer 00 01 02 03 04 05 06 07 8 09 20 01 02 03 04 05 06 07

Q 15 A small portion BCD of a very long straight wire is making a quadrant of a circle of radius r as shown in figure If current I is flowing through this resistance then find out value of magnetic field at the centre of circle A Zero B C 2 2 1 47 2 2 2 D Hol 2 2 1

24 An electron and proton enter in a uniform magnetic field perpendicularly Both have same kinetic energy Which of the following is true a Trajectory of electron is less curved b Trajectory of proton is less curved c Both trajectories are equally curved d Both move on straight line path

A long cylindrical thick wire of radius R has a cylindrical cavity of radius r Cross sectional view is shown in figure Current density is J Then 1 Magnetic field inside cavity is non uniform 2 Magnetic field near the wall of cavity is Hour 2

the page with the 5 41 The magnetic field B at all points within a circular region 5 45 of radius R is uniform in space and directed into the plane of char in figure 5 345 If the magnetic field is increasing at a rate dB dt what are the magnitude and direction of the force on a stationary positive point charge q located at points a b and c Point a is a distance r above the centre of the region point b is a distance r to the right of the centre and point c is at the centre of the region Ans At a qr 2 page at c zero dB dt B X R Figure 5 345 towards left at b X x b qrdB 2 dt towards top of the

A straight long conductor whose cross section is shown in the figure carries current uniformly distributed over the cross section for a rs b The variation of magnetic field with distance r from the axis is best represented by b a

A long straight stationary wire is parallel to the y axis and passes through the point Z h on the z axis A constant current I flows in this wire Lying in the x y plane is a thin rectangular loop with two of its sides of length 1 parallel to the long wire The length b of the other two sides is very small The loop slides with constant speed v in x direction For what values of x location of centre of the loop where the EMF induced is local maximum or minimum h A x 3h 2 B x C x 3h D x 0

A proton is thrown in an uniform magnetic field at an angle of 90 with the direction of field Then path of particle will be O Parabolic O Spiral O Circle O Linear

4 28 An airplane with a 20m wingspread is flying at 250 m s straight south parallel to the earth s surface The earths magnetic field has a horizontal component of 2 x 10 5 Wb m and the dip angle is 60 Calculate the induced e m f between the plane tips

5 56 A square frame with side a and a straight conductor carrying a constant current I are located in the same plane The e inductance and the resistance of the frame are equal to Land R respectively The frame was turned through 180 about the axis 00 separated from the current carrying conductor by a distance b as shown in figure 5 355 Find the electric charge having flown through the frame IA b a a 10

Two charged particles M and Nenter a space of uniform magnetic field with same velocities perpendicular to the magnetic field The paths are as shown in figure Then X X X X X X N Charge of Mis greater than that of N The momentum of Mis greater than that of N Specific charge of Mis greater than that of N

Q5 A beam of protons is accelerated through a potential difference of 0 745 kV and then enters a uniform magnetic field travelling perpendicular to the field a What magnitude of the field is needed to bend these protons in a circular arc of diameter 1 75 m b What magnetic field would be needed to produce a path with the same diameter if the particles were electrons having the same speed as the protons 7 points

A uniform magnetic field B Bo exists in space A particle of mass m and charge q is projected towards x axis with speed v from a point 0 0 The maximum value of v for which the particle does not hit the y plane is Boga m Boga 2m Bog am

A uniform circular ring of radius R has charge Q distributed uniformly over it A charge q is placed at the centre of the ring What is increase in tension in the ring Qq 4 ER 2Qq 7 ER Qq 8m R Qq