Electromagnetic Induction and Alternating Currents PDF

YATHARTH PHYSICS SUCCESS VALLEY ELECTROMAGNETIC INDUCTION AND 9. 1 henry is equal to: ALTERNATING CURRENTS (A) (B) (C) Weber ampere (D...

YATHARTH PHYSICS SUCCESS VALLEY ELECTROMAGNETIC INDUCTION AND 9. 1 henry is equal to: ALTERNATING CURRENTS (A) (B) (C) Weber ampere (D) None of these 1. The ratio of root mean square (rms) value and 10. The average value of ac over a complete cycle peak value of an alternative current is: is : (A) √2 (B) √ (A)𝐼 (B) (C) (D) Zero √ (C) (D) 2√2 11. The dimensional formula of L/R is similar to 2. Henry is unit of : that of: (A) Inductance (B) Magnetic flux (A) Frequency (B) time (C) Magnetic field (D) Electric field (C) Length (D) none of these 3. The unit of reactance is : 12. The dimensional formula of impedance is: (A) mho (B) ohm (A)[ML T A ] (B) [ML T A ] (C) farad (D) ampere (C) [ML T A ] (D) [ML T A ] 4. An a.c. source of angular frequency 𝜔 is 13. A choke is used as a resistance in connected in a series LCR circuit. The peak (A) DC circuits value of current will be maximum when : (B) AC circuits (A) 𝜔 < (B) 𝜔 < √𝐿𝐶 (C) both AC and DC circuits √ (C) 𝜔 = (D) 𝜔 > (D) (D ) either ' A' nor 'B' √ √ 14. The dimensional formula of induced emf is: 5. A cell of e.m.f. 1.5 V is connected with an (A)[ML T A ] (B) [ML T A ] ammeter of resistance of 0.05 Ω. If the current (C) [ML T A ] (D) [ML T A ] in the circuit is 2.0A, the internal resistance of 15. Transformer works on the principle of: the cell is: (A) Convertor (B) invertor (A) 1.0 Ω (B) 0.9 Ω (C) Mutual induction (D) self-induction (C) 0.8 Ω (D) 0.7 Ω 16. The band width of a series resonant circuit is: 6. The peak voltage of an a.c. is 440 yolt. Its (A) 𝑓 /𝑄 (B) virtual voltage is: (A) 220 V (B) 440 V (C) (D) 4R (C) 220 √2 V (D) 440 √2 V 17. A chock coil is a coil having: 7. If 𝜙 is the phase difference between a.c. (A) low inductance and high resistance current and e.m.f., then the value of power (B) low inductance and low resistance factor is : (C) high inductance and high resistance (A) tan 𝜙 (B) 𝑐𝑜𝑠 𝜙 (D) high inductance and negligible resistance (C) sin 𝜙 (D) cos 𝜙 18. Quantity that remains unchanged in a 8. Impedance of L-R circuit is: transformer is: (A) 𝑅 + 𝜔𝐿 (B) √𝑅 + 𝜔𝐿 (A) Frequency (B) current (C) 𝑅 + 𝜔𝐿 (D) √𝑅 + 𝜔 𝐿 (C) Voltage (D) None of these BEHIND MUNDDAP VIVAH BHAWAN, SANJAY CINEMA ROAD MUZAFFARPUR, 7903420719  YATHARTH PHYSICS SUCCESS VALLEY 19. Which quantity is increased in a step-down (A) Maxwell (B) Oersted trans-former? (C) Lenz (D) Faraday (A) Current (B) Voltage 28. Power factor of an ac circuit is a measure of : (C) Power (D) Frequency (A) virtual power 20. The peak voltage of 220 V A.C. mains is : (B) power lost in the circuit (A) 155.6 (B) 220 (C) mean power (C) 311 (D) 440 (D) all the above 21. The peak voltage in the output of wave 29. Energy dissipates in LCR circuit in: rectifier with a sinusoidal without filter is 10V. (A) L only (B) C only The d.c.component the output voltage is : (C) R only (D) All of the above (A) V (B) 10V 30. An iron core transformer with a turns ratio of 8:1 has 120 V applied across the primary. The (C) V (D) √ voltage across the secondary equals: 22. Which of the following is not equal to a (A) 15 V (B) 120 V henry? (C) 180 V (D)960 V (A) (B) 31. The magnetic flux linked with a coil is inversely (C) (D) proportional to the: (A) magnetic field (B) area of cross section 23. In an alternating current circuit, the phase (C) number of turns (D) none of the above difference between current I and voltage is 𝜙, 32. Instrument which converts mechanical energy then the Wattless component of current will into electrical energy is: be : (A) Induction-coil (B) Dynamo (A) 𝐼 cos 𝜙 (B) 𝐼 tan 𝜙 (C) Transformer (D) Motor (C) 𝐼 sin 𝜙 (D) 𝐼 cos 𝜙 33. Which quantity decreases in step-down 24. The magnetic flux (Φ) linked with a coil is transformer? related to the number of turns (N) of the coil (A) Current (B) Voltage as : (C) Power (D) Frequency (A) 𝜙 ∝ 𝑁 (B) 𝜙 ∝ 𝑁 34. The core of a transformer is laminated (C) 𝜙 ∝ 𝑁 (D) 𝜙 ∝ 𝑁 because: 25. The magnetic flux (𝜙) lined with a coil is (C) rusting of core may be prevented related to its area (s) as: (D) ratio of voltage in primary and secondary (A) 𝜙 ∝ 𝑠 (B) 𝜙 ∝ 𝑠 may be increased. (C) 𝜙 ∝ 5 / (D) 𝜙 ∝ 𝑠 / (E) energy losses due to eddy current may be 26. One henry is equal to : minimized (A) 10 mH (B) 10 mH (F) The weight of transformer may be (C) 10 mH (D) 10 mH reduced Ans. (C) 27. Who discovered that electric field is produced 35. The dimensional formula of the coefficient of in a conductor when magnetic lines of force self inductance is : intercepting it change? BEHIND MUNDDAP VIVAH BHAWAN, SANJAY CINEMA ROAD MUZAFFARPUR, 7903420719  YATHARTH PHYSICS SUCCESS VALLEY (A)[ML T ] (B) [ML T A ] (E) Power factor = (C) [ML T A ] (D) [ML T A ] (F) Power factor = 36. What is the ratio of inductive and capacitance (True average power x Apparent average power reactance’s in an AC circuit? 44. In L-C-R circuit to produce resonance : (A) 1 (B) 𝜔 𝐿 (A) 𝜔𝑐 = (B) 𝜔𝐿 = (C) 𝜔 𝐿𝐶 (D) 1 (C) 𝜔𝐿 = 𝜔𝑐 (D) None 37. In parallel resonant circuit : 45. Capacitive reactance is: (A) Impedance is very high (A) (B) (B) Current is very high (C) Voltage is very high (C) 𝑤. 𝑐 (D) (D) None of these 46. In A.C. circuit : 38. The Q factor of an LCR circuit at resonance is (A) frequency does not depend upon impedance (A) √𝑅 + 𝜔 𝐿 (B) 𝑅 + 𝐿𝜔 − (B) frequency increases with impedance (C) (D) 𝑅 + (C) frequency decreases with impedance 39. The band width of a series resonant circuit is: (D) frequency is inversely proportional to impedance (A) 𝑓 /𝑄 (B) 47. Which of the following is correct for (C) (D) 4R transformer? 40. The relation between r.m.s. value of (A) It converts A.C. into D.C. alternating current (𝐼.. ) and peak value of (B) It converts D.C. into A.C. alternating current (𝐼 ) is : (C) It increases or decreases D.C. voltage (A) 𝐼.. = 0.505𝐼 (B) 𝐼.. = 0.606𝐼 (D) It increases or decreases A.C. voltage (C) 𝐼.. = 0.707𝐼 (D) 𝐼.. = 0.808𝐼 48. If the equation of an electric current is 41. Inductive reactance offered by an inductor of 𝐼 = 0.6 sin 100𝜋𝑡 the, frequency of electric inductance L in ac circuit of angular frequency current is : 𝜔 is : (A)50 𝜋 (B) 50 (A) (B) 𝜔. 𝐿 (C) 100 𝜋 (D) 100 (C) (D) 49. The relation between peak current (𝐼 ) and. 42. Power factor in series LCR circuit is : Root mean square current (𝐼.. ) is: (A) R/Z (B) R.Z (A) 𝐼 = √2𝐼.. (B) 𝐼 = 𝐼.. (C)Z/R (D) 𝜔LR (C) 𝐼 = 2𝐼.. (D) 𝐼 =.. √ 43. Which of the following relations is correct for 50. Henery/Metre is the unit of: power factor? (A) Permittivity (B) Permeability (C) Power factor = (C) Self-Inductance (D) Mutual Inductance True average power x Apparent average power 51. Hot wire ammeter measures : (D) Power factor = (A) peak value of ac (B) average value of ac BEHIND MUNDDAP VIVAH BHAWAN, SANJAY CINEMA ROAD MUZAFFARPUR, 7903420719  YATHARTH PHYSICS SUCCESS VALLEY (C) r.m.s. ac (D) none of these 60. If phase difference between current and 52. If N1 and N2 are numbers of primary and potential difference is 𝜙 , then power factor secondary coils of a step-up transformer, then will be: (A) N > N (B) N > N (A)sin 𝜙 (B) cos 𝜙 (B) N = N (D) N = 0 (C) tan 𝜙 (D) None of these 53. The power factor of L-R circuit is : 61. S.I. unit of decay constant is: (A) 𝑅 + 𝑊𝐿 (B) (A) hertz (B) meter (C) per meter (D) none of these (C) 𝑅√𝑅 + 𝜔 𝐿 (D) WL/R 62. In A.C. circuit, the current and voltage are 54. When an ammeter is shunted, its measuring given by 𝑖 = 5 cos 𝑤𝑡 and 𝑉 = range: 200 sin 𝑤𝑡 respectively. Power loss in the (A) increases (B) decreases circuit is: (C) remains constant (D) none of these (A) 20 W (B) 40 W 55. The relation between peak current (𝐼 ) and (C) 1000W (D) zero Root mean square current (𝐼.. ) is: 63. The value of maximum amplitude produced (A) 𝐼 = √2𝐼.. (B) 𝐼 = 𝐼.. due to interference of two waves is given by (C) 𝐼 = 2𝐼.. (D) 𝐼 =.. √ 𝑦 = 4 sin 𝑤𝑡 and 𝑦 = 3 cos 𝑤𝑡. 56. A charge 'q' moves in a region where electric (A) 7 (B) 5 (C) 1 (D) 25 field ‘E’ and magnetic field 'B' both exist, then 64. The phase difference𝜙 is related to path force on it is : difference ∆𝑥 by : (A) 𝑞(𝑣⃗ × 𝐵⃗) (B) 𝑞 𝐸⃗ (A) 𝜙 (B) 𝜙 (C) 𝜙 (D) 𝜙 (C) 𝑞{𝐸⃗ + 𝑣⃗ × 𝐵⃗ } (D) 𝑞{𝐵⃗ + 𝑣⃗ × 𝐵⃗ } 65. Which of the following is correct for step-up 57. A circular coil of radius r carries a current I. transformer? The magnetic field at its centre is B. At what (A) 𝑉 < 𝑉 (B) 𝑉 > 𝑉 distance from the centre, or the axis of the (C) 𝑉 = 𝑉 (D) 𝑉 ≪ 𝑉 coil, the magnetic field will be B/8: 66. Inductive reactance for direct current is : (A)√2 𝑅 (B) 2 𝑅 (A) zero (B) infinity (C) √3 𝑅 (D) 3 𝑅 (C) 𝜔. 𝐿 (D). 58. Unit of is unit of: 67. Inductive reactance is : (A) 2R (A) 𝑋 = 2𝜋𝑓𝐿 (B) 𝑋 = 2𝜋𝑓 𝐿 (B)Lw (C) 𝑋 = 2𝜋𝑓𝐿 (D) 𝑋 = 2𝜋𝑓 𝐿 (C) Both A and 'B 68. Dimensional formula of R.C. is: (D) None of these (A) M L T (B) M L T 59. The convert a galvanometer into voltmeter (C) M L T (D) M L T requirement is 69. Transformation ratio in transformer is : (A) high resistance (B) low resistance (A) (B) (C) condenser (D) inductor (C) (D) BEHIND MUNDDAP VIVAH BHAWAN, SANJAY CINEMA ROAD MUZAFFARPUR, 7903420719  YATHARTH PHYSICS SUCCESS VALLEY 70. Phase difference in (L-R) circuit is: (A) sin (B) cos (C) tan (D) tan 71. The expression for real average power in an alternating current circuit is: (A) P = E cos ϕ (B) P = I cos ϕ (C) P = E I sin ϕ (D) P = E I cos ϕ 72. When current in a coil changes from 5A to 2A in 0.1 s then average voltage of 50 N is produced. The self-inductance of the coil is: (A) 1.67 Henry (B) 6 Henry (C) 3 Henry (D) 0.67 Henry 73. The formula for magnetic energy density for a solenoid is: (A) (B) (C) (D) 74. The self-inductance of a choke coil is 5 Henry. The current through it is increasing at rate of 2AS. The self-induced emf in the choke coil will be : (A)2.5V (B)5V (C) -10V (D)10V 75. The phase difference between current and voltage in only capacitive alternating current circuit is: 0 (A) 0 (B) 90° (C) 180° (D) 45° 76. For resonance condition in any L-C-R circuit, the phase difference between applied voltage and current is : (A) 𝜋 (B) (C) (D) zero 77. In step-up transformer, the value of current in secondary coil compared to primary coil is : (A) equal (B) less (C) more (D) none of these BEHIND MUNDDAP VIVAH BHAWAN, SANJAY CINEMA ROAD MUZAFFARPUR, 7903420719