Electromagnetic Induction Questions and Answers

A horizontal surface is rough A ring is placed on it with its plane parallel to the surface A charge 9 is uniformly Bot 3 2 distributed on this ring of radius R and mass m At t 0 a uniform magnetic field B QBOR 2mg The coefficient of friction is Find the time at which ring will start rotating about an axis perpendicular to its plane and passing through its centre in seconds 3 A B 1 C L is switched on r

R L elle 12 E R S R3 In the circuit shown the switch S has been open for a very long time It is suddenly closed at time t 0 Data E 180 V L 0 25 H C 4 10 F R 50 R 600 R3 a Find the current i on the emf device at time t 0 A 40 22 i 0 b Find the rate of change of the current on the inductor at time t 0 diz A s dt c Find the current i on the emf device at time t 0 i 0 A d Find the charge on the upper plate of the capacitor at time t o q 0 C

During the propagation of electromagnetic waves in a me dium a Both electric and magnetic energy densities are zero b Electric energy density is double of the magnetic en ergy density c Electric energy density is half of the magnetic energy density d Electric energy density is equal to the magnetic energy density

site signs ar ts downward increased a P is din a An emf of 15 volt is app 5 henry inductance and 10 92 resistance The ratio of the current at time t and t 1 s is e 1 2 1 6 A 31 A e e 1 3 1 e 1 4 e 1 If the armature resistance of a simple electric motor is 292 and runs at 24 volt It draws a current of 2A when the motor is unloaded But when it is connected with load then its speed reduces by 10 of its initial value The current taken by the loaded motor is 2 2 A 4 3 A Assertion Reason Type Que In the following questions a statem A is followed by a statement of 1 if both Assertion Rea reason is the correc assertion then mark SECTION 2 If both Assertion reason is not the assertion then m 3 If Assertion is false then ma 4 If both Ass statements 17 There are two coaxial solenoids S and S S surrounds S number of tums length are n and n radius r and r respectively If length of solenoids f mutual inductance is A The back R The cha motor 22 A The to c tra

luced A square loop enters a magnetic field with velocity v as shown in figure The front edge enters the magnetic field at time t 0 Which of the following graphs gives the correct variation of emf e induced in the loop with time t for its constant velocity in the magnetic field 1 3 1 2 A D t s 2 P t s 4 A rectangular metal loop ABCD is passed through ne magnetic field with a constant velocity v Which of the following represents power P vs time t graph B C V X X X X of dip is 45 B X t s t s X X X X X X X X X X 53 4 Self inductance of a solenoid is 5 mH If current is decreasing through it at the rate 103 A s then emf induced in the solenoid is 1 5 V 2 5 V 3 2 5 V 4 2 5 V Keeping number of turns constant self inductance L of a solenoid varies with its length las 1 LI 2 Lax 3 La R La 7 12 2 4 La b A conducting rod AC of length 41 is rotated with angular velocity w about a point O in a uniform magnetic field B directed into the plane of the paper If AO 1 and OC 31 then potential difference between A and C V Vis X x x X x x Ax X x S se X X X O X X x v X x X X X x 1 2Bw 2 Bw 3 3Bw 4 4Bw Tower 8 Pusa Road New Delhi 110005 Ph

1 3 3 1 2 A cylindrical space of radius R is filled with a uniform magnetic induction B parallel to the axes of the cylinder If B changes at a constant rate the graph showing the variation of induced electric field with distance r from the axis of cylinder is X Et n Et xx x t 20 4 Xx 2 E Et 58 A small circular loop of radius r is placed inside a circular loon of radius R Rad The 4 An anticlockwise induced curren the closed loop Figure below shows a square loop of resistance 10 2 The magnetic field H 8 1 0 T The work done in pulling the field slowly and uniformly in 2 s X x x X t x X x x x X X x x X X x x x TY 1 3 125 x 10 3 J 2 6 25 x 104 J 3 1 25 x 10 J 4 5 0 x 10 J 61 The wires P Q and P Q rails with the same speec towards left and P Q mov electric current in the 19 X H X PX P x x X X

A non conducting ring having a uniformly distributed negative charge is placed in the plane of smooth paper A uniformly decreasing inward magnetic field is passing through the ring Then 1 Ring will start rotating anticlockwise 2 Ring will start rotating clockwise 3 Ring will jump and becomes floating above the paper 4 No change will be observed in the position of the ring

16 A circular ring of radius square having side a a r The mutual inductance of the system is 1 Mor2 a 2 2 2 Horz 3 2 2 or a 4 2 2 Hor

E 2n Hb 1 4R L 3 3R x a a In 3 2n For the given R L circuit the time constant is R www 4 www 2R reee L 2 T 2 a 2T 2R 4 R 3L 4R 3 x L R tu For the given R L circuits the current through the cell just after switch is closed volt 3 2 volt 4 2 2 volt Two similar coaxial circular loops in the same direction On m apart the electric current will 1 Increase in both 2 Decrease in both 3 Remain unaltered 4 Increase in one and 23 Consider a thin metallic plane of the paper mov magnetic field B goin see fig If charge d on the left and righ sheet then Ignore

he slotting processes in a metallic sheet causes The increase of the resistance in the path for circulation of current 2 Decrease in the strength of eddy current 3 Feeble the electromagnetic damping AX All of these

P current carrying cable is penetrating a loop as shown in the figure If magnitude of current is decreasing with time then the current induced in the loop is C 1 Zero 2 Clockwise 3 Anticlockwise 4 Depends on the magnitude of current

4 1 An a particle is accelerated by a potential difference of 104 V Find the change in its direction of motion if it enters normally in a region of thickness 0 1m having transverse magnetic induction of 0 1 Tesla Given mass of a particle 6 4 10 7kg

Att 0 a wire loop in the shape of a right angled isosceles triangle PQR of side lengths QR RP a moving with constant speed v enters a region with a uniform magnetic field of strength B in a direction perpendicular to the plane of the loop The induced emf in the loop at t is N Bav Then the value of Nis a 5v R 013

11 A rectangular coil ABCD is placed near a long straight current carrying straight wire as shown What is the net force on the rectangular coil D C 2A 1A V1A 15 cm TEH A 10 cm 2 cm a 35 x 107 N towards the wire c 25 x 107 N towards the wire b 35 x 107 N away from the wire d 25 x 107 N away from the wire

th 1 The mber of rate of coil is 2019 then the input voltage JEE Main 2019 and current in the primary coil are a 220 V and 10 A c 440 V and 20 A Two coils P and Q are separated by some distance When magnetic flux of b 440 V and 5 A d 220 V and 20 A a current of 3 A flows through coil P a through Which of the following a 9 00 c 00 A planar loop of wire Initially at t 0 the the magnetic field If it axis in its plane then t maximum and minimu a 2 5 s and 7 5 s c 5 0 s and 10 0 s 103Wb passes through Q No current is passed through Q When no current passes through P and a current of 2 A passed through Q the flux through P is JEE Main 2019 a 6 67x10 Wb b 6 67 10 Wb c 3 67 10 Wb d 3 67x10 Wb

a X Jn Jn n n There are two long co axial solenoids of same length 1 The inner and outer coils have radii r and r2 and number of turns per unit length n and n respectively The rate of mutual inductance to the self inductance of the inner coil is JEE Main 2019 a 2 n2 r2 2 ni ri n Tot 1 d b 2 r1 n1 r2 n d n

A wave travelling in the ve x direction having displacement along y direction as 1 m wavelength 1 2 m and frequency of Hz is represented by T a y sin 10 x 20 t b y sin 2 x 2 t c y sin x 2t d v sin 2x 2 t NEFT 2013

There are two coils A and B linked through their magnetic flux The self inductance of coil A is 2 mH while that of B is 8 mH When the current in coil A is reduced from 4 A to 2 A in 4 s Which among the following cannot be the value of average induced emf in coil B X 1 V 0 5 V 1 5 V

Network shown in the figure is part of a circuit The current is 2 A and is decreasing at the rate of 2 A s Find the value of Vp Vo in volts P 10 V wwwwww 292 2 A 000000 2 H Answer 00 01 02 03 04 05 06 07 08 09 00 01 02 03 04 05 06 07 09

Consider the circuit shown in fig With switch S closed and the other two switches open the circuit has a time constant 0 05 sec With switch S closed and the other two switches open the circuit has a time constant 2 sec With switch S3 closed and the othe two switches open the circuit oscillates with a period T Find T in sec Taken 10 SKA I mmmmm L S C S3 www R THE

57 In a circuit L C and R are connected in series with an alternating voltage source of frequency f The current leads the voltage by 45 The value of C is 1 1 2 3 4 2nf 2nfL R 1 nf 2nfL R 1 2nf 2nfL R 1 ca KE

22 Two parallel conducting rails separated by a distance I are fixed on a plane surface inclined at an angle a to the horizontal as shown in figure Copper rod of mass m slides without friction on rails due to gravity A uniform vertical magnetic field exist throughout the region If at any instant velocity of rod is v the current through Ris 1 BA Bvl cos a R R www A 2 a ad Bvl tana R

20 A circuit containing resistors and an inductor Find the values of i soon after the switch S is closed and long after the switch S is closed 150 V 20 22 60 22 1 1 7 A 2 8 A 40 22 wwwww 3 H 00000000 S 2 1 2 A 24 A

A 4 pole d c generator has a wave wound armature with 792 conductors The flux per pole is0 0121 Wb Determine the speed at which it should be run to generate 240 V on no load

4 A flux of 25mWb links with a 1500 turn coil when a current of 34 passes through the coil Calculate a the inductance of the coil b the energy stored in the magnetic field and c the average e m f induced if the current falls to zero in 150ms

A uniform magnetic field 20 Texists in a gravity free space all over the space on right side of the shown boundary The given circular arc of radius 2 cm made of conducting wire of total resistance 4 9 is rotated around point O at a constant angular speed 2 rad per second Power required to maintain the constant angular velocity is 64 W 128 W A C B D 32 W 16 W cm 60 X X X X X x 20 X X X X X X X X X X X X X

Two identical charged particles moving with same speed enter a region of uniform magnetic field If one of these enters normal to field direction and the other enters along a direction at 30 with the field what would be the ratio of their angular frequencies 0 tonoid of 4000 If the

A very long carrying a current t kte at k 0 as a function of time t 0 taken as a Counter clockwise current to be positive A circular conducting coil of radius 2R is placed in the equatorial plane of the solenoid and concentric with the solenoid itself Then the current induced in the outer coil is correctly shown as a function of time by which of the following graph B t 0 adius N IS

A rigid conducting wire bent as shown is released to fall freely in a horizontal magnetic field which is perpendicular to the plane of the conductor If magnetic field strength is B then the emf induced across the point B and D when speed is v is X BL 1714

13 A rectangular coil of length 0 12 m and width 0 1 having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0 2 Weber m The coil carries a current of 2A If the plane of the coil is inclined at an angle of 30 with the direction of the field the torque required to keep the coil in stable equilibrium will be 1 0 24 Nm 3 0 15 Nm 2 0 12 Nm 4 0 20 Nm m

A solenoid has 2000 turns wound over a length of 0 30 m The area of its cross section 1 2 x 10 m Around its central section a coil of 300 turns wound If an initial current of 2 A in the solenoid is reversed in 0 25 s then the emf induced in the coil is equal to 8 6 10 V B 4 8 x 10 2 V Correct Answer 1 2 10 V 2 6 0 10 V EXPLANATION di 140 N N A de dt 4TX10 7x2000 300 1 2 10 4 Emf Mdi dt 0 3 0 25

A rod of length 2 is rotating about one of its ends with angular velocity w If a magnetic field Bo exists in parallel with axis of rotation then find emf developed across the end points of rod 0 1 2B 01 O BowR 03 2B 01 5

1 r has its centre at the origin of the coordinate system in a magnetic field of induction B When it is rotated about y axis through 90 the net charge flown in the loop is directly proportional to y 1 R 1 2 2 2 R

A conducting loop slides on a horizontal frictionless table into a square region of uniform magnetic field as shown Which graph is the most appropriate option showing the speed v of the loop as a func tion of time t V 1 VI t 2 V V t

35 On a fixed inclined plane two conducting rails are fixed A conducting rod of length L is placed on the two rails as shown in the figure 1 The conducting rod has mass m and it can slide on the rails without friction There exists a uniform magnetic field B vertically upward in the region At an instant the conducting rod is released from rest The terminal velocity of the rod will be 2 4 mgR cose BL sin e mgR sine B3L mgr sine BL cos e R mgR BL sin e Bo

7 The e m f induced in a pure inductor of inductance 100 mH is 3t2 2 V If at t 0 current through the inductor is 0 then the current through it at time t 2 s will be 1 160 A 2 120 A 3 140 A 4 220 A

According to Lenz s law of electromagnetic induction The induced emf in the direction opposing the change in magnetic flux The relative motion between coil and magnet produces no change in magnetic flux in any case Only magnet should be moved towards coil Only the coil should be moved towards magnet

36 A coil of inductance 5H is joined to a cell of emf 6V through a resistance of 10 2 at t 0 The potential difference across the coil at time t In 2 sec is 1 3V 3 0 75 V 2 1 5 V 4 4 5 V

Two circuits are shown in the figure a b At a frequency of rad s the average power dissipate in one cycle will be same in both the circuits 50 R 220 V 40 F C 50 R 220 V 0 1 H mooooo L

3 6 mH 31 Find potential difference between A and C if potential difference between A and B at a certain instant is 12 V 1 12 V 3 36 V 0000000 6 H B ooooooo 4 H 0000000 12 H 2 24 V 4 Zero A

A capacitor of capacitance 1 mF originally charged to a potential difference of 10 V is connected to an inductor of inductance L If the maximum current in the circuit is 10A find the value of inductance L in mH Assume inductor to be ideal 10V L C000009 1 mF

D variable resistor Q53 Why inductance of toroid is more than the inductance of a solenoid having same number of turns core of same material and similar size A Core is endless hence there no leakage of flux B Resistance of wire is less hence magnitude of current flow is more G Number of turns per unit length is more D Both A and B

In the following part of a circuit i 5 A dl 3 As 12 2A 4 A s Find VA VB dt 2H2V 3V 3H 39 Awwwwwwwww B 20 al www 40 4 V 4H T JEE Foundations Jucational Services Limited

a CD b DE c AB d BC 10 Which of the following statements is not correct a Whenever the amount of magnetic flux linked with a circuit change an emf is induced in circuit b The induced emf lasts so long as the change in magnetic flux continues c The direction of induced emf is given by Lenz s law d Lenz s law is a consequence of the law of conservation of momentum

12 The south pole of a bar magnet is rapidly moved towards one face let us say A of a coil Which of the following statements correctly depicts the phenomenon taking place No induced emf is developed The face A of the coil behaves like a south pole The face A of the coil behaves like north pole d The face A of the coil acquires zero potential

39 Switch is in position A for a long time It is suddenly switched to the side B Mass of rod is m and lengt 1 Maximum speed of rod will be 1 F E L R A B 000000 L I m I m 2 7 R E m OB

Find current i at time t 0 and time t in the following circuits R a c L 000000 R 3R 6R E 3R www R 000000 000000 L wwww 3R R r d www 2R R www www 2R www L www R oundations Education Svices Limited

In the circuit shown in figure charge varies with time as q q 1 e IRC The correct option about the rate of heat produced in resistance R with time is A B G C E R E R e E e E D t RC 2t RC t RC R www

ing square loop of side L and resistance R moves in its plane with a uniform velocity v perpendicular to one of its sides A magnetic induction B constant in time and space pointing perpendicular and into the plane at the loop exists everywhere with half the loop outside the field as shown in figure The induced emf is a zero d v BL b RvB c vBL R 113

A coil has an area of 0 05 m and it has 800 turns It is placed perpendicularly in a magnetic field of strength 4 x 105Wb m it is rotated through 90 in 0 1 second The average emf induced in the coil is 1 0 056 V 2 0 046 V 3 0 026 V I