Tiêu đề EECTROMAGNETICS INDUCTION (EMI).pdf ✅

Electromagnetic Induction  Digital www.allendigital.in [ 169 ] MAGNETIC FLUX 1. 'SI' unit of magnetic flux is :- (1) ampere/meter2 (2) weber (3) gauss (4) oersted 2. A square coil of 0.01 m2 area is placed perpendicular to the uniform magnetic field of 103 weber/m2. The magnetic flux linked with the coil is :- (1) 10 weber (2) 10–5 weber (3) Zero (4) 100 weber FARADAY LAW & LENZ’S LAW 3. According to Faraday's Laws of electromagnetic induction: (1) The direction of the induced current is such that it opposes itself (2) The induced emf in the coil is proportional to the rate of change of magnetic flux associated with it (3) The direction of induced emf is such that it opposes itself (4) None of the above 4. A coil having an area of 2m2 is placed in a magnetic field which changes from 1 Weber/m2 to 4 Weber/m2 in 2 seconds. The e.m.f. induced in the coil will be :– (1) 4 volt (2) 3 volt (3) 2 volt (4) 1 volt 5. Magnetic field through a coil is changed with respect to time and an emf is induced in it. Select the incorrect statement regarding induced emf in coil :- (1) Coil may be made up with wood (2) Coil may be connected with an open circuit (3) Coil must be of conducting nature (4) Induced emf does not depends upon resistance of the coil 6. The current flows in a circuit as shown below. If a second circuit is brought near the first circuit then the current in the second circuit will be :- (1) Clock wise (2) Anti clock wise (3) Depending on the value of RG (4) None of the above 7. A coil of resistance 10 and 1000 turns have the magnetic flux line of 5.5  10–4 Wb. If the magnetic flux changed to 5  10–4 Wb. in 0.1 sec, then the induced charge in coil is :– (1) 50 C (2) 5 C (3) 2 C (4) 20 C 8. One coil of resistance 40 is connected to a galvanometer of 160 resistance. The coil has radius 6mm and turns 100. This coil is placed between the poles of a magnet such that magnetic field is perpendicular to coil. If coil is dragged out then the charge through the galvanometer is 32C. The magnetic field is:- (1) 6.55 T (2) 5.66 T (3) 0.655 T (4) 0.566 T 9. A square loop of side 22 cm is changed to a circle in time 0.4 s. The magnetic field present is 0.2 T. The emf induced is :- (1) –6.6 mV (2) –13.2 mV (3) +6.6 mV (4) +13.2 mV 10. The magnetic flux in a coil of 100 turns increases by 12 × 103 Maxwell in 0.2 s due to the motion of a magnet. The emf induced in the coil will be:- (1) 0.6 mV (2) 0.6 V (3) 6 V (4) 60 V 11. A closed coil consists of 500 turns on a rectangular frame of area 4.0 cm2 and has a resistance of 50 ohms. The coil is kept with its plane perpendicular to a uniform magnetic field of 0.2 wb/m2, the amount of charge flowing through the coil if it is turned over (rotated through 180°):- (1) 1.6 × 10–3 C (2) 16 × 10–3 C (3) 0.16 × 10–3 C (4) 160 × 10–3 C Observer v Exercise - I
NEET : Physics [ 170 ] www.allendigital.in  Digital 12. A coil of mean area 500 cm2 and having 1000 turns is held perpendicular to a uniform field of 0.4 gauss. The coil is turned through 180o in 1 10 second. The average induced e.m.f. :– (1) 0.04 V (2) 0.4 V (3) 4 V (4) 0.004 V 13. An emf is induced in a coil. The linking magnetic flux (1) Must be decreasing (2) Must be increasing (3) Must remain constant (4) Can be either increasing or decreasing 14. Consider a metal ring kept on a horizontal plane. A bar magnet is held above the ring with its length along the axis of the ring. If the magnet is dropped freely the acceleration of the falling magnet is (g is acceleration due to gravity) :- (1) More than g (2) Equal to g (3) Less than g (4) Depend on mass of magnet 15. An electron beam is moving near to a conducting loop then the induced current in the loop :- (1) clockwise (2) anticlockwise (3) both (4) no current 16. The current flows from A to B as shown in the figure. The direction of the induced current in the loop is :- (1) clockwise (2) anticlockwise (3) straight line (4) none of these 17. Faraday law represents :- (1) relation between I and B (2) relation between magnetic force and magnetic field (3) relation between e.m.f and rate of change of flux (4) none of these 18. 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 19. A charge particle moves along the line AB, which lies in the same plane of a circular loop of conducting wire as shown in the fig. Then :- (1) No current will be induced in the loop (2) The current induced in the loop will change its direction as the charged particle passes by (3) The current induced will be anticlockwise (4) The current induced, will be clockwise 20. The magnetic flux through a circuit of resistance R changes by an amount  in a time t. The total quantity of electric charge Q that passes any point in the circuit during the time t is represented by:– (1) Q = R  (2) Q = t   (3) Q = R . t   (4) Q = 1 R . t   Magnet Ring S N A B A A B I A B
Electromagnetic Induction  Digital www.allendigital.in [ 171 ] 21. If number of turns of 70cm2 coil is 200 and it is placed in a magnetic field of 0·8 Wb/m2 which is perpendicular to the plane of coil and it is rotated through an angle 180° in 0·1 sec, then induced emf in coil :- (1) 11.2 V (2) 1.12 V (3) 22.4 V (4) 2.24 V 22. A circular loop of radius r is placed in a region where magnetic field increases with respect to time as B(t) = at then induced emf in coil :- (1) r 2a (2) 3r 2a (3) 2r 2a (4) 4r 2a 23. A circular loop of radius r is moved away from a current carrying wire then induced current in circular loop will be :- (1) Clock wise (2) Anti clockwise (3) Not induced (4) None of them SELF INDUCTION AND L–R DC CIRCUIT 24. When the current through a solenoid increases at a constant rate, the induced current (1) is a constant and is in the direction of the inducing current (2) is a constant and is opposite to the direction of the inducing current (3) increase with time and is in the direction of the inducing current (4) increase with time and opposite to the direction of the inducing current 25. A solenoid of 10 henry inductance and 2 ohm resistance, is connected to a 10 volt battery. In how much time the magnetic energy will reach to 1/4th of the maximum value? (1) 3.5 sec (2) 2.5 sec (3) 5.5 sec (4) 7.5 sec 26. An inductance coil have the time constant 4 sec, if it is cut into two equal parts and connected parallel then new time constant of the circuit :- (1) 4 sec (2) 2 sec (3) 1 sec (4) 0.5 sec 27. Which statement is correct from following – (a) Inductor store energy in the form of magnetic field (b) Capacitor store energy in the form of electric field (c) Inductor store energy in the form of electric and magnetic field both (d) Capacitor store energy in the form of electric and magnetic field both (1) a, b (2) a, c (3) b, d (4) b, c 28. If a current of 2A give rise a magnetic flux of 5 × 10–5 weber/turn through a coil having 100 turns, then the magnetic energy stored in the medium surrounding by the coil is :- (1) 5 joule (2) 5 × 10–7 joule (3) 5 × 10–3 joule (4) 0.5 joule 29. For a solenoid keeping the turn density constant its length makes halved and its cross section radius is doubled then the inductance of the solenoid increased by :– (1) 200% (2) 100% (3) 800% (4) 700% 30. A constant current I 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 the 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 31. The inductance of a solenoid is 5H and its resistance is 5. If it is connected to a 10 volt battery then time taken by the current to reach 9/10th of its maximum will be :- (1) 4.0 s (2) 2.3 s (3) 1.4 s (4) 1.2 s 32. An LR circuit with a battery is connected at t = 0. Which of the following quantities is not zero just after the connection :- (a) Current in circuit (b) Magnetic potential energy in the inductor (c) Power delivered by the battery (d) Emf induced in the inductor (1) a, b (2) a, c (3) c, d (4) Only d i v
NEET : Physics [ 172 ] www.allendigital.in  Digital 33. During 0.1s current in a coil increases from 1A to 1.5A. If inductance of this coil is 60 H, induced current in external resistance of 600  is :- (1) 1A (2) 4/3 A (3) 2/3 A (4) 1/2 A 34. In the circuit shown in figure what is the value of I1 just after pressing the key K ? (1) 5 7 A (2) 5 11 A (3) 1A (4) None of the above 35. Pure inductors each of inductance 3H are connected as shown. The equivalent induction of the circuit is :- (1) 1H (2) 2H (3) 3H (4) 9H 36. The time constant of an inductance coil is 2.0 × 10–3 s. When a 90  resistance is joined in series, the time constant becomes 0.5 × 10–3 s. The inductance and resistance of the coil are :- (1) 30mH ; 30 (2) 30mH ; 60 (3) 60mH ; 30 (4) 60mH ; 60 37. A cylindrical iron core supports N turns. If a current I produces a magnetic flux  across the core's cross section, then the magnetic energy is :- (1) I (2) 1 2 I (3) 2 I 2  (4) I2 38. The self-inductance of a toroid is (N: no. of turns, r: radius of cross section, Rm:mean radius of toroid) :- (1) 2 2 0 m N r 2R  (2) 2 0 m N r 2R   (3) 2 0 m N r 2R  (4) 2 0 m N r R   39. An inductance L and a resistance R are joined to a battery. After some time, battery is disconnected but L and R remains connected to the closed circuit. The current strength will be reduced to 37% of its initial value in : (1) RL sec (2) R/L sec (3) L/R sec (4) 1/LR sec 40. Energy is stored in the choke coil in the form of:- (1) Heat (2) Electric field (3) Magnetic field (4) Electro-magnetic field 41. When a current changes from 2A to 4A in 0.05 sec. in a coil, induced emf is 8 V. The self inductance of coil is :- (1) 0.1 H (2) 0.2 H (3) 0.4 H (4) 0.8 H 42. An e.m.f. of 12 V is induced in a given coil when the current in it changes at the rate of 48 A/min. The inductance of the coil is :– (1) 0.5 henry (2) 15 henry (3) 1.5 henry (4) 9.6 henry 43. Two conducting coils are placed co-axially now a cell is connected in one coil then they will :- (1) attract to each other (2) repel to each other (3) both (1) & (2) (4) they will not experience any force 44. A coil of resistance 10 and an inductance 5H is connected to a 100V battery. Then energy stored in the coil is :- (1) 125 erg (2) 125 J (3) 250 erg (4) 250 J 45. The energy density in magnetic field B is proportional to :- (1) 1 B (2) 2 1 B (3) B (4) B2 K 10V 8 I1 2mH I3 8 6 P Q