Tiêu đề 21. Electromagnetic Induction.pdf ✅

1. If the coefficient of mutual induction of the primary and secondary coils of an induction coil is 5 H and a current of 10 A is cut off in 5 × 10–4 s, the emf inducted (in volt) in the secondary coil is :- (1) 5 × 104 (3) 25 × 105 (2) 1 × 105 (4) 5 × 106 2. A square loop of wire, side length 10 cm is placed at an angle of 45° with a magnetic field that changes uniformly from 0.1T to zero in 0.7 seconds. The induced current in the loop (its resistance is 1 ) is :- (1) 1.0 mA (2) 2.5 mA (3) 3.5 mA (4) 4.0 mA 3. An aluminium ring B faces an electromagnet A. The current I through A can be altered. Then which of the following statement is correct :- (1)If I decreases A will repel B (2)Whether I increases or decreases, B will not experience any force (3)If I increases, A will repel B (4)If I increases, A will attract B 4. A current carrying loop is placed in a uniform magnetic field in four different orientations, I, II, III & IV. Arrange them in the decreasing order of potential energy (1) I > III > II > IV (2) I > II > III > IV (3) I > IV > II > III (4) III > IV > I > II 5. A square metallic wire loop of side 0.1 m and resistance of 1  is moved with a constant velocity in a magnetic field of 2 wb/m2 as shown in figure. The magnetic field is perpendicular to the plane of the loop, loop is connected to a network of resistances. What should be the velocity of loop so as to have a steady current of 1mA in loop (1) 1 cm/sec (2) 2 cm/sec (3) 3 cm/sec (4) 4 cm/sec 6. As shown in the figure a metal rod makes contact and complete the circuit. The circuit is perpendicular to the magnetic field with B = 0.15 Tesla. If the resistance is 3, force needed to move the rod as indicated with a constant speed of 2m/sec is 7. Two solenoids have identical geometrical construction and same number of turns but one is made of thick wire and other of thin wire. Which of the following quantities are different for two solenoids – (a) Self inductance. (b) Rate of joule heating if the same current goes through them. (c) Magnetic potential energy if the same current goes through them . (d) Time constant. (1) b, d (2) a, c (3) b, c (4) All above 8. A metallic frame moves v with constant velocity v near a infinite length current carrying wire. At any instant induced emf in sides AD and BC are 5 V and 2V respectively. If resistance of frame is 6  then magnitude and direction of induced current in it – (1) 2 A, ACW (2) 0.5 A, ACW (3) Zero (4) 0.5 A, CW Electromagnetic Induction
9. Two coils X and Y are placed in a circuit such that when a current changes 2A in coil X, the magnetic flux changes by 0.4 weber in Y. The value of mutual inductance of the coils - (1) 0.2 H (2) 5 H (3) 0.8 H (4) 20 H 10. A uniform magnetic field B exists in a cylindrical region of radius 10 cm as shown in figure. A uniform wire of length 80cm and resistance4.0  is bent into a square frame and is placed with one side along a diameter of the cylindrical region. If the magnetic field increases at a constant rate of 0.010 T/s, find the current induced in the frame – (1) 3.9 × 10–5 A (2) 8 × 10–5 A (3) 18 × 10–5 A (4) 6 × 10–5 A 11. A bar magnet is moved along the axis of a copper ring placed far away from the magnet. Looking from the side of the magnet, an anticlockwise current is found to be induced in the ring. Which of the following may be true – (1) The south pole faces the ring and the magnet moves towards it (2) The north pole faces the ring and the magnet moves towards it (3) The north pole faces the ring and the magnet moves away from it (4) None of these 12. Which is correct for phenomenon of periodic electromagnetic induction - (1) Phase difference between induced emf and induced current is  (2) Phase difference between induced emf and linked flux is zero (3) Phase difference between induced emf and linked flux is  /2 (4) Frequency of all induced parameters is double the rotational frequency of the coil 13. A conducting loop is placed in a uniform magnetic field with its plane perpendicular to the field. An emf is induced in the loop if – (a) It is translated (inside the field) (b) It is rotated about its axis (c) It is rotated about a diameter (d) It is deformed (1) a,b (2) b,c (3) c,d (4) a,c,d 14. A field line shown in the figure. This field line cannot represent – (1) magnetic field (2) electrostatic field (3) induced electric field (4) All of above 15. A conducting loop of radius R is present in a uniform magnetic field B perpendicular the plane of the ring. If radius R varies as a function of time ‘t’, as R = R0+ t. The e.m.f induced in the loop is:- (1) 2(R0 + t)B clockwise (2) (R0 + t)B clockwise (3) 2(R0 + t)B anticlockwise (4) zero 16. A vertical bar magnet is dropped from the shown position on the axis of a fixed metallic coil as shown in fig - I. In fig - II the magnet is fixed and horizontal coil is dropped. The acceleration of the magnet and coil are a1 and a2 respectively then
(1) a1> g , a2> g (2) a1> g , a2< g (3) a1< g , a2< g (4) a1< g , a2> g 17. A uniform magnetic field exists in region given ˆ ˆ ˆ B i j k = + + 3 4 5 . A rod of length 5 m is placed along y − axis is moved along x − axis with constant speed 1 m/sec. Then induced e.m.f. in the rod will be: (1) zero (2) 25 volt (3) 20 volt (4) 15 volt 18. Two identical conducting rings A & B of radius r are in pure rolling over a horizontal conducting plane with same speed (of center of mass) v but in opposite direction. A constant magnetic field B is present pointing inside the plane of paper. Then the potential difference between the highest points of the two rings, is : (1) zero (2) 2 Bvr (3) 4Bvr (4) none of these 19. A square loop of side 1m is placed in a perpendicular magnetic field. Half of the area of the loop inside the magnetic field. A battery of emf 10 V and negligible internal resistance is connected in the loop. The magnetic field changes with time according to relation B = (0.01 – 2t) Tesla. The resultant emf in the loop will be (1) 1 V (2) 11 V (3) 10 V (4) 9 V 20. A conducting rod PQ of length L = 1.0 m is moving with a uniform speed v = 2 m/s in a uniform magnetic field B = 4.0T directed into the paper. A capacitor of capacity C = 10 F is connected as shown in figure. Then (1) qA = + 80 C and qB = – 80 C (2) qA = – 80 C and qB = + 80 C (3) qA = 0 = qB (4) Charge stored in the capacitor increases exponentially with time 21. Flux  (in weber) in a closed circuit of resistance10 ohm varies with time t (in sec) according to the equation  = 6t2− 5t +1 . What is the magnitude of the induced current at t = 0.25 s ? (1) 1.2 A (2) 0.8 A (3) 0.6 S (4) 0.2 A 22. A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be (1) Anticlockwise (2) Clockwise (3) East (4) West 23. A coil of 10–2H inductance carries a current I = 2 sin (100 t)A. When current is half of its peak value at that instant the induced emf in the coil is :- (1) V (2) 2 V (3) 3V (4) 2V 24. A constant current is maintained in a solenoid. Which of the following quantities will increase if an iron rod is inserted in the solenoid along its axis? (a) Magnetic field at centre (b) Magnetic flux linked with the solenoid (c) Self inductance of the solenoid (d) Rate of joule heating (1) a, b, c (2) c, d (3) a, b (4) only b 25. One turn of insulated wire in the form of a planar square frame with side l = 0.2 m and resistance 1  is placed in a uniform magnetic field perpendicular to the magnetic field lines. The current passing through the turn when magnetic field starts to decrease at a constant rate of 0.1 T/s is :- (1) 4 mA (2) 2 mA (3) 1 mA (4) 0 26. The inductance of a solenoid is 5 H and its resistance is 5  . If it is connected to a 10 volt battery, then time taken by current to reach 9 10 of its maximum value is :- (1) 4.0 s (2) 2.3 s (3) 1.4 s (4) 1.2 s 27. An inductor of inductance L = 400 mH and resistance R1 = 2  and R2= 2 are connected
to a battery of emf 12 V as shown in the figure. The internal resistance of the battery is negligible. The switch S is closed at t = 0. The potential drop across L as function of time is :- 28. A fully charged capacitor C with initial charge q0 is connected to a coil of self inductance L at t = 0. The time at which the energy is stored equally between the electric and magnetic field is :- 29. A jet plane is travelling towards west at a speed of 1800 km/h. What is the voltage difference developed between the ends of the wing having a span of 25 m. If the Earth's magnetic field at the location has a magnitude of 5 × 10–4 the dip angle is 30°: (1) 3.125 volt (2) 3.12 volt (3) 6.5 volt (4) None 30. Kamla peddles a stationary bicycle the pedals of the bicycle are attached to a 100 turn coil of area 0.10 m2 . The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.01T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil :- (1) 3. 125 volt (2) 0. 314 volt (3) 31. 2 volt (4) 3. 14 volt 31. Find time constant for given circuit :- 32. In the circuit initially switch S is open the S is closed at t = 0 the difference between the maximum and minimum current that can flow in the circuit is :- (1) 2 Amp (2) 3 Amp (3) 1 Amp (4) Nothing can be concluded 33. A and B are two metallic rings placed at opposite sides of an infinitely long straight conducting wire as shown . If current in the wire is slowly decreased the direction of induced current will be (1) Clockwise in A and anticlockwise in B (2) anticlockwise in A and clockwise in B (3) clockwise in both A and B (4) anticlockwise in both A and B 34. When a 'J' shaped conducting rod is rotating in its own plane with constant angular velocity  about one of its end P, in a uniform magnetic field B directed normally into the plane of paper then magnitude of emf induced across it will be :- 35. A conducting rod PQ of length 5m oriented as shown in fig. is moving with velocity ( ) 2 / m s i ˆ without any rotation in a uniform magnetic field ( ) ˆ ˆ 3 4 j k + tesla. Emf induced in the rod is :-