Electromagnetic Induction Questions and Answers

In the figure shown is a R L circuit connected with a cell of emf through a key k If key k is closed find the current drawn by the battery a just after the key k is closed b long after the key k is closed P R R C 2R L RS

A metallic ring of mass 2 kg and radius 1m with a uniform metallic spoke of same mass 2kg and lengt 1 m is rotated about its axis with angular velocity 1 rev sec in a perpendicular uniform magnetic field B of magnitude 10T as shown if figure If the central end of the spoke is connected to the rim of the whee through a resistor R of magnetiude 2 as shown The resistor does not rotate its one end is always a the center of the ring and other end is always in contact with the ring A force F as shown is needed t maintain constant angular velocity of the spoke then F is equal to The ring and the spoke has zem resistance 2 110 A 10 N F BIL Ragna a que spoke 43 67 Himmens B1m 15 TM COUHIA B 20 N and an dad del art spoke K R vafra art spoke fa B E ata frufe Ru R a mi yo f m g n c z a as qpja vu fay fuargar da Fe X xxx Fx C 50 N D 30 N 2 kg

A conducting rod of mass m and radius r is rotating at constant oo in uniform magnetic field B as shown in diagram at t 0 The value of i at any time t is t L R D D R Bar www D2 X 0000000 L X rod m r X X 7

In the circuit shown switch S is initially open and switch S is initially closed At time 0 S is close and at time t 0 25 s S is opened The voltage across the inductor V S 10V 1H oooooo 10 V 2002 A Just after switch S is closed V 2 B Just before switch S is opened V 10 eV C Just after switch S is opened V 40 50 e V D Just after switch S is opened V 60 50 e V L 50

The ends of a search coil having 20 turns area of cross section 1 cm and resistance 2 ohr connected to a ballistic galvanometer of resistance 40 ohms If the plane of search coil is incli 30 to the direction of a magnetic field of intensity 1 5 Wb m coil is quickly pulled out of th to a region of zero magnetic field calculate the charge passed through the galvanometer The total flux linked with the coil having turns N and area A is

Q6 A solenoid 25 0 cm long and with a cross sectional area of 0 500 cm contains 400 turns of wire and carries a current of 80 0 A Calculate a the magnetic field in the solenoid b the energy density in the magnetic field if the solenoid is filled with air c the total energy contained in the coil s magnetic field assume the field is uniform 7 points and d the inductance of the solenoid

There is a metallic ring of radius 1 m having negligible resistance placed perpendicular to a constant magnetic field of magnitude 1 T as shown in figure One end of a resistanceless rod is hinged at the centre of ring O and other end is placed on the ring Now the rod is rotated with constant angular velocity w 4 rad s and circuit is connected as shown in the figure initially switch is open and capacitor is uncharged If switch S is closed at t 0 then the heat loss in J in the resistor R from t 0 to the instant when voltage across the capacitor becomes half of the steady state voltage ignore friction is ang gadu 1 m Aru y s faz i zef xgar 1 1 9kay aud zu Glazi c Au du 6 0 42 hafa au gun A day 42 2 14 21 3 03 h Aua clufu acc Aud u w 4 rad sou a r send uzmz uta ku ja M Ma a ka i u Gal a t 0 34 G4 z acca zu c ufa ug R 7 71 adu ch aqug R 102 wwwww R 20 2 C 3 F

angement is moving towards left with speed v then potential difference between B and C are respectively X X X X B X VE X Xx X X A 2R LR B R C 2 4 D X X X X and non zero 2BvR and zero and non zero 4BvR and zero ional Services Limited Regd Office Aakash Tower 8 Pusa Road New Delhi 110005 Ph

For the RC circuit shown in figure at steady state switch S is closed at t 0 Power in W dissipated in resistors just after the switch is closed is 18 V 392 www 602 C S Answer 00 01 02 03 04 05 06 07 08 09 C C 30 C

If resistance of voltmeter is 40 then error in reading of voltmeter is 5n Find the value of n www 2092 www 40 92 60 V Answer 01 02 03 04 05 06 07 08 09 0 01 02 03 04 05 06 07

A beam of protons moving with velocity 106 m s enters a uniform magnetic field of 0 5 T The velocity makes an angle of 37 with the magnetic field The pitch of the helical path followed by protons will be 2 4 cm O 3 2 cm 1 6 cm 3 6 cm

In an EM wave the electric and magnetic fields are pe True False Question 4 1 point For infrared light shorter wavelengths go with Temperature doesn t matter Hotter objects

34 A transverse magnetic field is confined in a cylindrical region 34 of radius 5 cm magnetic field is increasing at the constant rate of 0 01 T sec What is the instantaneous value of electric field at surface of cylindrical region 1 2 5 x 10 V m 2 2 5 x 10 V m 3 5 x 10 V m 4 5 x 10 V m 1 2 5 x 10 V m 3 5 x 10 V m f 0 01 T sec 2 2 5 x 10 V m 4 5 x 10 V m

What percent is the initial value should be taken So tha t change can be calculated Pls explain it 5 15 When the number of turns and the length of a solenoid are doubled percentage change in the self inductance is 25 X 50 200

A charge particle q m enters magnetic field region of width d as shown Magnetic field inside the region is uniform and equal to Bo If d then distance mvo 2qBo travelled by the particle before it exits the field region is Vo O X X X X X X X nd 3 X X X X X X X d X X X X X X X X

If resistance of voltmeter is 40 Q then error in reading of voltmeter is 5n Find the value of n www 20 92 www 40 92 60 V Answer 00 01 02 03 04 05 06 07 08 09

A metallic square wire loop of side 10 cm and resistance 12 is moved with a constant velocity vo in a uniform magnetic field of induction B 2 T as shown in the figure The magnetic field perpendicular to the plane of the loop The loop is connected to a network of resistors each of value 3 ohm The resistance of the lead wires OS and PQ are negligible What should be the speed of the loop so as to have a steady current of 1 mA in it Give the direction of current in the loop 1 2 x 10 2 m sec anticlockwise direction 2 4 x 10 2 m sec anticlockwise direction 3 2 x 10 2 m sec clockwise direction 4 4 x 10 2 m sec clockwise direction ix X X X ix X X X X X X 30 352 302 302

In the given arrangement the loop is moved with constant velocity v in a uniform magnetic field B in a restricted region of width a The time for which the emf is induced in the circuit is b a O O 26 2a XXX X X X X X X X X X XXX XXX

3 To measured a magnetic field between the magnetic poles of a loud speaker a small coil having 30 turns and 2 5 cm area is placed perpendicular to the field and removed immediately If the total charge flown through the coil is 75 x 10 C and the total resistance of wire and galvanometer is 0 3 2 then the magnitude of the magnetic field is a 0 03 T b 0 3 T c 3 T d 3 10 T

Q 23 Two conducting rails are connected to a source of emf and form an incline as shown in figure A bar of mass 50 g slides without friction down the incline through a vertical magnetic field B If the length of the bar is 50 cm and a current of 2 5 A is provided by battery Value of B for which the bar slide at a constant velocity X10 Tesla g 10 m s 0 37 B 1 2 ur IO HO SO D 2

An equilateral triangular wire frame of side length I as shown has a total resistance R It is being pulled with speed v out of the region where there is a uniform field B pointing out of the page What is the value of force F required to be applied to the frame so that it moves with constant speed v when its left corner is at distance 1 4 inside the magnetic field TAD GJAR YM A yg a g Ayucr az o ci ha ufa u R 1 3 34 a h g 32 ja 3 q i q zy Bh j 3 A ka da 21 ho ruch an F che Suc qui hau ghhu ga 3 42 1 4 z uz 6 fud i v fa d a O O B peng F B 1 v 16R B 1 v 12R F Correct Answer 2 2

A metal rod PQ slides on parallel smooth conducting rails of negligible resistance and having a separation of 50 cm The resistance of the rod PQ is 2 Q An ideal battery of emf 10 V is connected as shown There is a uniform field of magnitude 2 5 T directed perpendicular and into the plane of paper A force F 2 5 N is required to move rod PQ with a constant velocity v Then choose the correct statement s Ich wach PQ 3 uu ufa u 50 cm Ag udh ucku uz Maadi Q 2 0 1 f 10 V nef azt send gmz iu a fu ga i 2 5 Yh Ghou da c atda ay such 31 42 A 313 AZRa da 71 g3 PQ fua u v fan ch a i f F 2 5 V da si a cs 10 V B X D X X X X X X P X X X X A The value of vis 11 2 m s V11 2 m s Correct Answer V The value of vis 8 m s 8 m s The current in the rod PQ is 1 A PQRT 1 A The current in the rod PQ is 2 A PQRT 2 A Correct Answer

45 A conductor rod AB moves parallel to x axis in a uniform magnetic field pointing in the positive x direction The end A of the rod gets A positively charged B negatively charged C neutral D first positively charged and then negatively charged O O O O B O O O olo OO O O O

38 Radius of a circular ring is changing with time and the coil is placed in uniform magnetic field perpendicular to its plane The variation of r with time t is shown in figure Then induced emf e with time t will be best represented by 14 I I La A A B C D

In a coil of resistance 10 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 4 0 1 6 3 8 0 1 t s 2 4 4 2

2 100 10 24 2 200 contains three diodes each with forward resistance of 50 homs and with infinite backward resistance If the battery voltage is 6V the current through the 100 bhm resistance is SU ic 1 0 2 36 mA 3 43 mA 4 50 mA AZ KH 36 40 20 150 2 www 20 3 32 12 50 2 www 50 92 www V CR 100 C wwwwww 80 Avalanche breakdown in

Two circular coils can be arranged in any of the three situations shown in the figure Their mutual inductance will be Je a b A Maximum in situation a B Maximum in situation b C Maximum in situation c D The same in all situations c

A car moves on a plane road Induced emf produc across the axle is maximum when it moves 1 2 3 4 At the poles Moves at equator Remains stationary No emf is induced at all Correct Answer 1

The length of a magnet is large compared to it s width and breadth The time period of its oscillation in a vibration magnetometer is T The magnet is cut along it s length into six parts and these parts are then placed together as shown in the figure The time period of this combination will be N S N S SN S N SN

2 4 An ideal 25 kVA transformer has 500 turns on primary winding and 40 turns on the secondary winding the primary is connected to 300 volt 50 Hz supply calculate 1 Primary and secondary current on full load II secondary emf iii maximum flux

Please explain the e and f part in detail What is the e ffect of tapping key being just realeased or being just clos ed 6 1 EXERCISES Predict the direction of induced current in the situations described by the following Figs 6 18 a to f Tapping key just closed vos Common axis X Tapping key just released e y Common axis Rheostat setting being changed dy Current I decreasing at a steady rate

3 An auto transformer supply a load of 5 kilowatt at 125V and at unity power factor if the primary voltage is 250 volt determined 1 Transformation ratio II secondary current III primary current IV number of turns across the secondary if total number of turn is 250 V power transformed

PHYSICS SECTIC Question No 28 Multiple Choice Question A step up transformer is used on a 120V line to provide a potential difference of 2400V If the primary coil has 75 turns the numb A O 1575 1200 B C O 150 D O 1500

A plane spiral coil is made of a thin insulated conducting wire and has 100 turns Radii of the inside and outside tums are 10 cm and 20 cm respectively A uniform magnetic field normal to the plane of spiral exist in space The magnetic field increases at a constant rate 0 3 Tesla sec A wire of resistance 1 12 is connected between the ends of the spiral Find the current in A induced in the resistance wire to the closest integer Resistance of the spiral coil is neglected

A rectangular coil of area 0 2 m is held in a magnetic fiel of strength 2T in such a way that the normal to the plan of the coil makes an angle 30 with the field What is th flux linked with the coil 0 346 Wb

7 34 In a series connection between a coil and a bulb across a steady source predict the observation when an iron core is inserted in the coil Now the do supply is replaced by ac source What is the observation Mark only one oval bulb glows with equal brightness in both the cases bulb glows dimly in former case and brightly in the latter case bulb goes off in both cases bulb s illumination is unaffected in former case but glows dimmer in latter one

1 A thin semicircular conducting ring of radius R is falling with its plane vertical in a horizontal magnetic induction B At the position MNQ the speed of the ring is v and the potential difference developed across the ring is x X X X B M X X 1 zero 2 BV R 2 and Mis at higher potential 3 TRBV and Q is at higher potential 4 2RBv and Q is at higher potential X N X X V X X X X x X Q

A closed circular coil having a diameter of 50 cm and of 200 turns with a total resistance of 10 is placed with its plane at right angles to a magnetic field of strength 10 2 T Calculate the quantity of electric charge that flows through it when the coil is turned through 180 about its diameter 0 078C

29 26 As shown in Fig below P and Q are two coaxial conducting loops separated by some distance When the switch S is closed a clockwise current Ip flows in P as seen by E and an induced current Iq1 flows in Q switch remains closed for a long time When S is opened a current lq2 flo in Q Then the directions of Iq1 and Iq2 as seen by E are Mark only one oval 0000 clockwise and anticlockwise respectively both clockwise both anticlockwise anticlockwise and clockwise respectively A E

A conducting wire of length 30 cm revolves 1000 times per minute about one of its ends and perpendicular to the direction of a magnetic field of 0 5 T Determine the emf induced across the ends of the wire 2 355 V

21 18 A rectangular loop carrying a current I is situated near a long straight wire 1p such that the wire is parallel to one of the sides of the loop and is in a plane of the loop If a steady current I is established in the wire as shown in Fig below the loop will Mark only one oval 0000 rotate about an axis parallel to the wire move away from the wire towards right move towards the wire but does not rotate remain stationary

Respected teacher in the given question as we are movin g the south pole of the magnet towards the coil wont the flux decrease So which option should be correct As shown in the figure a magnet is moved with a fast speed towards a coil at rest Due to this induced e m f induced current and induced charge in the coil is E I and Q respectively If the speed of the magnet is doubled the incorrect statement is 1 E increases N S 2 4 mmmmm increases Q increases magnet moves in and out of the coil

For the series LCR circuit shown in figure what is the resonance angular frequency and the amplitus of current at resonance angular frequency FLORUR fer un angle af SHIP 220 V 4 mH DET 550 A OPTIONS MARK FOR REVIEW CLEAR SELECTION 40 C 2500 rad s and 48 A A 2500 rad s

Two positive charge each of magnitude q are placed at the two comer of an equilateral triangle of side a The net force on a third negative charge of magnitude 2q placed at the centre will be T MI GRAN yang 29 de gem OPTIONS MARK FOR REVIEW CLEAR SELECTION A 340 6kg

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 1 It is translated along the axis of ring 2 It is translated in the plane of the ring 3 It is rotated about its axis 4 It is rotated about one of its diameter 34

Assertion The presence of large magnetic flux through a coil maintains a current in the coil if the circuit is continuous Reason Magnetic flux is essential to maintain an Induced current in the coil A B C D Both Assertion and Reason are correct and Reason is the correct explanation for Assertion Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion Assertion is correct but Reason is incorrect Both Assertion and Reason are incorrect

The current I in the inductance is varying with time according to the plot shown in figure Which one of the following is the correct variation of voltage with time in the coil a T 2 T b T 2 T t T 2 CC

A conducting disc of radius a and mass m is kept rotating with a constant angular speed in a horizontal plane about a vertical axis in a uniform vertical magnetic field B as shown in figure One metal contact B is made at the circumference of the disc and another contact B is made in such a way that its distance from centre is always a 2 If the switch S is closed at t 0 then the value of current in the inductor Value of n is B x x at t In2 is R en R L S 3Boa nR B a 2 xxxx

34 A conducting rod of mass m and length place on smooth horizontal surface in a region wher transverse uniform magnetic field B exist A t 0 a constant force F start acting on the rod a its mid point as shown Potential differenc between ends the rod Vp V at any time t is BXL X X X X X X X 1 X X X X X p BF lt 2m 5BFlt X X X X X Ve X X X W X X X X 30 X X X 2 X XQx Jo X X X X X X X BF lt 4m 7BFlt X X X X X X X Ofex

21 A superconducting loop of radius R has self inductance L A uniform constant magnetic field B is applied perpendicular to the plane of the loop Initially current in this loop is zero The loop is rotated by 180 The current in the loop after rotation is equal to A zero B B R L C 2BTR L D BAR 2L