Electromagnetic Induction Questions and Answers

7 A solenoid of length 20 cm area of cross section 40 cm and having 4000 turns is placed inside another solenoid of 2000 turns having a cross sectional area 8 0 cm and length 10 cm Find the mutual inductance between the solenoids Ho 200 of nodius R and having

A toroid is having 100 turns inner radius 9 cm and outer radius 11 cm then its self inductance is 1 2 H 2 Ho 2 3 Ho 5 4 5 Ho

Area of cross section of plane circular coil makes twice keeping it number of turns same then percantage increases in its self inductance 1 41 4 3 200 2 141 4 4 100

d low 1 A circuit contains a capacitor and inductance each with negligible resistance The capacitor is initially charged and the charging battery is disconnected At subsequent time the charge on the capacitor will b decrease exponentially a increase exponentially d remain constant c decrease linearly for limiting

A uniform and constant magnetic field B coming out of the plane of the paper exists in a rectangular region as shown in figure A conducting rod PQ is rotated about its mid point O with a uniform angular speed win the plane of the paper The emf EpQ induced between P and Q is best represented by the graph PQ P B

graph of B versus x abruptly 51 Sometimes we show an idealised magnetic field which is uniform in a given region and falls to zero One such field is represented in figure 35 E12 Using Ampere s law over the path PQRS show that such a field is not possible S 10 B Figure 35 E12 S Q R 59

of earth s magnetic A 255 m wide spaceship moves through the space at a speed 4 5 x 10 m s A magnetic field B 8 x 105T exists in the space in a direction parallel to the plane of motion Treating the spaceship as a conductor calculate the emf induced across its width

COMPREHENSION VIII A thin circular ring of mass m radius R has a uniformly distributed charge Q The ring is placed on a rough horizontal floor The coefficient of friction between the ring and the floor is u A uniform vertically upward magnetic field of radius greater than R and co axial with the ring exists in the space The magnetic field is changing as B Bot2 tesla where t is the time in second where Bo is a positive constant Now answer the following questions based on the above paragraph 26 C Choose the correct graph showing the variation of induced electric field with time t at the circumference of the ring A E B E E D Q M E B

2 A pair of coils of turns n and n are kept close together Current passing through the first is reducing at rate r and e m f 3 mV is developed across the other coil If the second coil carries current which is then reduced at the rate 2r the emf produced across the first coil will be 1 6n mV n 3 6 mV 2 6n2 mV n 3 4 mV

3 In a cylindrical region uniform magnetic field which is perpendicular to the plane of the figure is increasing with time and a conducting rod PQ is placed in the region Then a P will be at higher potential than Q b Q will be at higher potential than P d no omf will be developed

The magnetic field of a cylindrical mag net that has a pole face radius 2 8 cm can be varied sinusoidally between the minimum value 16 8 T and the maxi mum value 17 2 T at a frequency of 50 Hz Cross section of the magnetic field created by the magnet is shown in Fig 3 211 At a radial distance of 2 cm from the axis find the amplitude of the electric field in units ofx 10 mNC induced by the magnetic field variation Fig 3 211 X X X X X X X X X 2 8 cm X X X X X X X

A thin circular ring of mass m radius R has a uniformly distributed charge Q The ring is placed on a rough horizontal floor The coefficient of friction between the ring and the floor is u A uniform vertically upward magnetic field of radius greater than R and co axial with the ring exists in the space The magnetic field is changing as B Bot tesla where t is the time in second where Bo is a positive constant Now answer the following questions based on the above paragraph b umg Find the Time at which the Ring Starts Rotating 4 Mmg 3B QR BQR M

Magnetic field through a coil is changed with respect to time then emf induced in it then select the incorrect regarding induced emf in coil 1 Coil may be made up with wood 2Coil may be connected with an open circuit 3 Coil must be of conducting nature Induced emf does not depends upon resistance of the coil ct

A conducting rod of length L is rotating about a perpendicular axis passing through point O as shown in figure The potential difference between ends M and Nis Y 2x7 1 M BOL 27 BOL X X X X X X X X X X 2L 3 X X X X X X XX X X X X X X X X X X X X X x O X X 100 2 1 X 13 L XX X X X BOL 6 BWL XX N X R E al BEN 2 2ZXW YU B 24

3d The new value of the 1 2 F 2 F 3 4 7 2F 3 The length of a magnet is large compared to its width and breadth The time period of its oscillation in a vibration magnetometer is 2s The magnet is cut perpendicular to its length into three equal parts and three parts are then place on each other with their like poles together The time period of this combination will be AIEEE 2004 1 2s 2 2 3s 3 2 3 s 4 2 3 s HO AIEEE 2004

29 30 A current loop ABCD is held fixed on the plane of the paper as shown in the figure The arcs BC radius b and radius a of the loop are joined by two straight wires AB and CD A steady current I is flowing in the loop An made by AB and CD at the origin O is 30 Another straight thin wire with steady current I flowing out of the plane AIEEE 200 the paper is kept at the origin 3 aA 9 30 The magnitude of the magnetic field due to the loop ABCD at the origin O is l b a MI b a 4 ab 24ab H 2 b a a b 4T 2 B 4 zero Due to the presence of the current I at the origin 1 The forces on AD and BC are zero HI I 2 The magnitude of the net force on the loop is given by 4t II 3 the magnitude of the net force on the loop is given by 24ab 4 the forces on AB and DC are zero a a b 2 b a a b a

NEET PHYSICS All India Major Test Ser Q 129 A thin semicircular conducting ring PQR of Q 12 radius r is falling with its plane vertical in a horizontal magnetic field B as shown in figure O 1x x P B Rx The potential difference developed across the ring when its speed is v is 1 By and R is at higher potential 2 2rBv and R is at higher potential 3 Zero

In an oscillating LC circuit the maximum current on the inductor is i The current in the inductor when the energy is stored equally between the electric and magnetic fields is Question Type Single Correct Type 1 1 2 2 1 3 3 1 2

A coil having 200 turns has a surface area 0 12 m A magnetic field 32 34 0 10 Wbm 2 linked perpendicular to this area changes to 0 5 Wbm2 in 0 2 s Find the average emf induced in the coil Ans 48 V

A conducting bar of 2 m length is allowed to fall freely from a 50 m high tower keeping it aligned along the east west direction Find the emf induced in the rod when it is 20 m below the top of the tower g 10 ms 2 Earth s magnetic field is 0 7 x 104 T and angle of dip 60 Ans 1 4 mV

An observer is at 2 m from an isotropic point source of light emitting 40 W power What are the rms values of the electric and magnetic fields due to the source at the position of the observer c 3 x 108 m s 8 854 x 10 2 C N m Ans E rms 17 3 V m B 5 77 x 10 8 T rms A plane electromagnetic wave travelling along X direction has electric field of amplitude 300 V m directed along the Y axis a What is the intensity of the wave b If the

An AC generator s coil has 2000 turns and is rotated with angular speed of 500 rad s If the area of the coil is 10 cm and the magnetic field is 0 2 T then the peak voltage in the coil will be 100 V 600 V 200 V 300 V

Electromagnetic wave consists of periodically oscillating electric and magnetic vectors In mutually perpendicular planes but vibrating with a phase difference of In mutually perpendicular planes but vibrating with a phase difference of TU 2 In randomly oriented planes but vibrating in phase In mutually perpendicular planes but vibrating in phase

61 the circuit shown in figure below the ammeter A reads 1 6 A and ammeter A3 reads 0 4 A If wo is angular frequency and f is frequency of ac then 4 1 0 LC 2 f 2 LC L 88000000 A3 A ac A C 3 The ammeter A reads 1 2 A 4 The ammeter A reads 2 A la tho ac sours

r rotates about its axis 49 A conducting disc of ra with an angular speed w in a uniform magnetic field A resistance R is connected between centre and rim of the disc then B Jo R AH AWWWB C 1 No em f will induce across resistance 2 E m f will induce and A is at high potential 3 Current in resistance will flow from A to B 4 Resistance becomes hot due to Joule s heating 17623456 52

60 Figure below shows a square loop of side 0 5 m and resistance 10 2 The magnetic field has a magnitude B 1 0 T The work done in pulling the loop out of the field slowly and uniformly in 2 second is V X X X X X X X X X X X X 1 3 125 x 10 J 2 6 25 10 4 J 3 1 25 10 J 4 5 0 10 4 J X X X X X X X X X X X xx X x X XX X X X X X X

17 An inductor of inductance L a capacitor of capacitance C and a resistor of resistance R are connected in series across E E sin The reading of hot wire voltmeter connected across resistor is 1 E E 2 Eo t LC 4 Zero 23

41 A light of wavelength medium of refractive index 1 5 Frequency and wavelength of light in the medium respectively are 1 5 x 1014 Hz 6000 5 x 1014 Hz 4000 3 4 10 3 10 3 x 1014 Hz 4000 x 1014 Hz 6000

The ratio of inductive reactance of an inductor when connected with a source of frequency 10 Hz and 40 Hz respectively is 1 2 1 4 2 3 5 4

The two coils of self inductance 4 H and 4 H are wound on the same iron core The coefficient of mutual inducta for them may be 4 H 10 H 20 H 64 H

Question The magnitude of emf induced in a 2 mH inductor in which the current changes from 8 A to 6 A in 10 sece 2 x 10 6 V 8 x 10 6 V 4 V 8V

How many meters of a thin wire are required to manufacture a solenoid of length 1 100cm and inductance L 1mH if the solenoid s cross sectional diameter is considerably less than its length 1 100 L 1mHaki R FIT A B C D fyrf da I S N BIERZENI su 1 0 km 0 10 km 0 010 km 10 km

A proton moves with a constant speed of 50 m s along the x axis through crossed electric and magnetic fields which are perpendicular to each other If the magnetic field is 2 x 10 3 T along the negative z direction what is the corresponding electric field JOL to tartoo A 0 1 V m along positive y direction B 0 1 V m along negative y direction C 1 6 10 18 V m along positive y direction D 1 6 10 18 V m along negative v direction

14 The straight wire AB carries a current I The ends of the wire subtend angles 8 and 8 at t point P as shown in figure The magnetic field at the point P is a c Hol 4 Hol 4ra sin 0 sin 0 cos 0 cos 0 B A 0 P b d Hol 4 Hol 4 sin 0 sin 0 cos 0 cos 0 are loons A B and C Identify

5 At the centre of a fixed large circular coil of radius R a much smaller circular coil of radius r is placed The two coils are concentric and are in the same plane The larger coil carries a current I The smaller coil is set to rotate with a constant angular velocity about an axis along their common diameter Calculate the emf induced in the smaller coil after a time t of its start of rotation a c Mol wr sin oot 4R Mol sin oot 2R b d Mol AR MO 2 R 00 sin cot 002 sin oot

919 A copper wire is wound on a wooden frame whose shape is that of an equilateral triangle If the linear dimension a factor of 3 of each side of the frame is increased by keeping the number of turns of the coil per unit length of the frame the same then the self inductance of the coil a increases by a factor of 27 b decreases by a factor of c increases by a factor of 3 d decreases by a factor of 9

When a monochromatic source of light is at a distance of 0 2 m from a photoelectric cell the cut off voltage saturation current are respectively 0 6 V and 18 mA If the same source is placed 0 6 m away from the cell th 1 the stopping potential will be 0 2 V 3 the saturation current will be 6 0 mA 2 the stopping potential will be 1 8 V 4 the saturation current will be 2 0 mA

b Two concentric circular loops of radius 1 cm and 20 cm are placed coaxially i Find mutual inductance of the arrangement ii If the current passed through the outer loop is changed at a rate of 5 A ms find

A vertical ring of radius r is made of a uniform wire of resistance R It slips vertically between two frictionless and resistanceless vertical rails There is a uniform magnetic field B perpendicular to plane of ring and rails as shown in figure When the speed of ring is v then the current in section PQ at that NBvr 2R Value of N is instant is XXXX X X X X X X XXXX X X X X

gement shows two long metallic rails connected to resistance R forming an inclined plane Magnetic field is vertical in the region If slider of mass m and length will move with the terminal am NmgR sin 0 velocity incline is smooth B cos e then value 0 of Nis R www 0 l m B 0

A starter is required for a 220 V shunt motor The maximum allowable current is 55 A and the minimum current is about 35 A Find the number of sections of starter resistance required and the resistance of each section The armature resistance of the motor is 0 4 2

A 6 pole 50 Hz 3 phase induction motor running on full load develops a useful torque o 160 Nm when the rotor emf makes 120 complete cycles per minute Calculate the shaft power output If the mechanical torque lost in friction and that for core loss is 10 Nm Compute a the copper loss in the rotor windings b the input to the motor and c the efficiency The total stator loss is given to be 800 W

24 Two concentric and coplanar circular coils have radii a and b a as shown in figure Resistance of the inner coil is R Current in the outer coil is increased from 0 to i then the total charge circulating the inner coil is Hoia 2Rb a c Hoi b 2a R b ats b Hoiab b b 2R d Ho ib 2 R

A B Two conducting rings A and B are placed in a time varying magnetic field Both are made of identica wires and the radius of A is twice that of B TH induced current in A is 1 equal to that in B 3 half that in B 2 4 twice that in B four times that in

CP Electromagi Magnetic flux in weber linked with a closed circuit of resistance 10 ohm varies with time t in seconds as 6 5 4t 1 The induced electromotive force in the circut at t 0 2 sec is 1 0 4 volts 2 0 4 volts 3 2 0 volts 2 0 2 0 volts 07 tot 2 L

2 3 weber 0 5 weber B Bo p 0 02 cos 100nt weber turns and number of turns is 50 in the coil the maximum induced emf is 4 6 28 volt 2 0 weber 3 weber 2 314 volt 2 100 volt 3 31 4 volt netic flux linked with the coil varies with time as d 3t 4t 9 The magnitude of induced emfatt

A 30 cm by 40 cm rectangular loop rotates at 130 rad s in a magnetic field 0 06 Wb m normal to the axis of rotation If the loop has 50 turns determine the induced voltage in the loop

As shown in figure two vertical conducting rails separated by distance 1 0 m are placed parallel to z axis At z 0 a capacitor of 0 15 F is connected between the rails and a metal rod of mass 100 gm placed across the rails slides down along the rails If a constant magnetic fields of 2 0 T exists perpendicular to the plane of the rails what is the acceleration of the rod Take g 9 8 m s AIIMS 2017 HT 3 9 8 m s 4 zero

In a coil of resistance 102 the induced current developed by changing magnetic flux through it is shown in figure as a function of time The magnitude of change in flux through the coil in Weber is i amp O 216 0 1 t s 4 4 AIPMT 2012

XY as sh the path of electron What will be the direction of current if any induced in the coil Please explain what when start movin ll happen ectron afters crossing with diagram a abcd a d O C b adcb c The current will reverse its direction as the electron goes past the coil