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IIT JEE Electromagnetic Induction Electromagnetic Waves Part-1

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1. The electromagnetic waves of much short wavelength (25 mm to 5 mm) were produced and observed by:




2. A transformer has an efficiency of 80% and works at 100 V and 4 kW. If the secondary voltage is 240 V then the value of primary current is:




3. Electromagnetic waves are transverse in nature is evident by:




4. A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis then:




5. An inductance has a high resistance to AC and low to DC. When a DC voltage source having same AC component superimposed on it sends current through an inductance to a load resistance:




6. The conduction current is same as displacement current when source is:




7. The reactance of an inductor connected with DC voltage is:




8. In L-R circuit the time constant is given by:




9. According to Faradays law the total charge induced in a conductor that is moved in a magnetic field depends upon:




10. If a current of 3 A flowing in the primary coil is reduced to zero in 001 s then the induced emf in the secondary coil is 1500 V the mutual inductance between the two coils is:




11. The resonant frequency of a series circuit consisting of an inductance 200 ?H a capacitance of 00005 ?F and a resistance of 10? is:




12. he average value for half cycle in a 200 V AC source is:




13. An electric charge oscillating with a frequency of 1 kilo cycles/s can radiate electromagnetic waves of wavelength:




14. The frequency of voltage for an AC circuit if the equation of alternating voltage is V = 200 sin 314t is:




15. In a step-up transformer the number of turns in:




16. A fully charged capacitor is allowed to discharge through an inductor of 05 mH The initial current through the inductance rises from 0 to 15 A in 25?s The instantaneous voltage across it is:




17. In an electromagnetic wave the average energy density is associated to:




18. The nature of electric field in the region between the two plates of a capacitor while charging is:




19. Which one of the following can produce maximum induced emf?




20. An output voltage of E = 170 sin 377t is produced by an AC generator where t is in sec then the frequency of alternating voltage will be:




21. If 20 V battery is connected to primary coil of a transformer then output voltage is:




22. If a dry cell of emf 1.5 V is connected across the primary of a step-up transformer of turn ratio 3: 4 then the voltage developed across the secondary is:




23. In a series L-C-R circuit the voltage across each resistance inductance and capacitance is 10 V If the resistance is short-circuited the current in the circuit will be:




24. The magnetic field between the plates of radius 12 cm separated by distance of 4 mm of a parallel plate capacitor of capacitance 100 pF along the axis of plates having conduction current of 015 A is:




25. An AC circuit consists of a resistance and a choke in series. The resistance is of 220? and choke is of 0.7 H. The power absorbed from 220 V and 50 Hz source connected with the circuit is:




26. A point source of electromagnetic radiation has an average power output of 800 W. The maximum value of electric field at a distance 4.0 m from the source is:




27. Two pure inductor coils of self-inductance L each are connected in series the net inductance is:




28. The correct sequence of the increasing wavelength of the given radiation sources is:




29. When the current through a solenoid increases at a constant rate the induced current:




30. A motor




31. Induction coil is based on the principle of




32. The core of any transformer is laminated so as to:




33. In an L-C-R circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged the inductance should be changed from L to:




34. A choke coil is preferred to a rheostat in AC circuit then:




35. In the case of dc motor if the current flowing through the armature coil minimum induced emf is




36. A 50 mH coil carries a current of 2 A the energy stored in joule is:




37. The induced e. m. f. in a coil rotating in a uniform magnetic field depends upon




38. What is the mutual inductance of coil and solenoid if a solenoid of length 0.50 m and with 5000 turns of wire has a radius 4 cm and a coil of 700 turns is wound on the middle part of the solenoid?




39. In step-up transformer the turn ratio is 1:2. A leclanche cell (emf = 1.5V) is connected across the primary the voltage developed in the secondary would be:




40. Iron core chokes are used for reducing low frequency ac because




41. A closed circuit consists of a source of emf E and an inductor coil of inductance L connected in series The active resistance of whole circuit is R At the moment t = 0 inductance of coil abruptly decreased to L/n Then current in the circuit immediately after is:




42. When the current changes from +2 A to -2A in 005 s an emf of 8V is induced in a coil The coefficient of self-induction of the coil is:




43. A coil is rotated in a uniform magnetic field about an axis perpendicular to the field. The emf induced in the coil would be maximum when the plane of coil is:




44. The voltage of domestic AC is 200 V. What does this represent?




45. A coil of wire of radius R has 200 turns and a self-inductance of 108 mH. The self-inductance of a similar coil of 500 turns will be:




46. When the speed of the coil of generator is increased




47. One 10 V 60 W bulb is to be connected to 100 V line. The required self-inductance of induction coil will be: (f = 50 Hz)




48. The time constant of C-R circuit is:




49. A 50 Hz AC current of crest value 1 A flows through the primary of a transformer. If the mutual inductance between the primary and secondary be 0.5 H the crest voltage induced in the secondary is:




50. If a current increases from 0 to 1 A in 0.1 s in coil of 5 mH then the magnitude of the induced emf will be:




51. A coil of inductance L = 300 mH and resistance R = 140 m? is connected to a constant voltage source. Current in the coil will reach to 50% of its steady value after time t equal to:




52. In the case of charging or discharging of a capacitor RC has units of




53. A coil is wound on a frame of rectangular cross-section If the linear dimensions of the frame are double and the number of turns per unit length of the coil remains the same then the self inductance increases by a factor of




54. Current in a 10 milli henry coil increases uniformly from zero to one ampere in 0.01 second then the value of induced e. m. f. is




55. A resistor and an inductor are connected to an ac circuit whose supply is 200 V. An ac voltmeter across R reads 150 V. This voltmeter across inductor will read nearly




56. In LR circuit the time constant is given by




57. The current drawn from the primary of a transformer which steps down 220 V to 22 V at 0.1 amp. Shall be




58. A copper plate flat pendulum and a copper plate pendulum with slots in it but of same dimension are made to oscillate in a magnetic field. Then




59. When a coil moves towards a stationary magnet the induced emf does not depend upon




60. Self-induction opposes the growth of current in a circuit when the current is




61. A cylindrical magnet is kept along the axis of a circular coil In rotating the magnet about its axis the coil will have induced in it




62. A generator produces 22 KW of power at 100 A at 220 V. The length of transmission line is 100 Kilometre whose resistance is 1 ohm. The line loss will be




63. Self-inductance is measured in




64. A step up transformer is used on 120 V line to provide a P. D. of 2400 V. If the number of turns is 75 then the number of turns in the secondary shall be




65. A power transmission line feed input power at 2200 V to a step down transformer with its primary windings having 3000 turns in secondary windings should be