Practice Test

Q1) The energy stored in an inductance is 1 joule when a current of 0.1 ampere is established in it. The self - inductance of the coil is Show Answer

Q2) The areas of cross-section of two solenoids A and B of equal length are equal but the number of turns in the solenoid A is double than that of B. If the coefficient of self-induction of B is 6 mH, then the coefficient of self-induction of A will be Show Answer

Q3) A copper ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is Show Answer

Q4) Keeping all other factors same, the number of turns of a coil is doubled. The magnetic flux linked with the coil is Show Answer

Q5) Induction furnace is based on the heating effect of Show Answer

Q6) Lenz's law is consequence of the law of conservation of Show Answer

Q7) An artificial satellite with a metal surface is moving about the earth in a circular orbit. A current will be induced in the satellite, if Show Answer

Q8) A solenoid has n turns. If coefficient of self inductance L varies with n as Show Answer

Q9) A conducting rod PQ moves parallel to x-axis in a uniform magnetic field, pointing in the negative z-direction. The end P of the rod gets Show Answer

Q10) Which of the following statements is correct ? Show Answer

Q11) A circular coil of radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self-induction of the coil will be Show Answer

Q12) A rod of length 20 cm is rotating with angular speed of 100 revolutions per minute in a magnetic field of strength 0.5 T. What is the potential difference between two ends of the rod ? Show Answer

Q13) The coefficient of mutual - inductance of two circuits A and B is 3 mH and their respective resistance are 10 ohm and 4 ohm. How much current should change in 0.02 second in the circuit A, so that the induced current in B should be 0.006 ampere ? Show Answer

Q14) A coil whose diameter is 0.40 m is in a variable magnetic field. As the magnetic induction of the field changes by 127.4 T during 2 s, an emf of 200 V is induced in the coil. Then the number of turns in the coil is approximately Show Answer

Q15) An emf of 6 V is introduced in a given coil when the current in it changes at the rate of 30 A/min. The inductance of the coil is Show Answer

Q16) When the number o turns in a coil is doubled without any change in the length of the coil, its self-inductance becomes Show Answer

Q17) In a circular conducting coil, when current increases from 2 A to 18 A in 0.05 s, the induced emf is 20 V. The self-inductance of the coil is Show Answer

Q18) Which of the statements, about a solenoid, is correct ? Show Answer

Q19) A metallic rod of 1 m length is rotated with a frequency of 50 rev/s with one end hinged at the centre and the other end at the circumference of circular metallic ring of radius 1 m, about an axis passing through the centre and perpendicular to the plane of the ring. A constant and uniform magnetic field of 1 T parallel to the axis is present everywhere. The emf between the centre and the metallic ring is Show Answer

Q20) The expression for the magnetic energy stored in a solenoid in terms of magnetic field B, area A and length l of the solenoid is Show Answer

Q21) Current in a circuit falls from 5 A to 0 A 0.1 s. If an average emf of 200 V is induced, give an estimate of the self-inductance of the circuit Show Answer

Q22) A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, what is the change of flux linkage with the other coil Show Answer

Q23) A light bulb is rated at 100 W for a 220 V supply. The peak voltage of the source is Show Answer

Q24) A pure inductor of 25 mH is connected to a source of 220 V. Find the rms current in the circuit if the frequency of the source is 50 Hz. Show Answer

Q25) Suppose the frequency of the source in the previous questions can be varied, what is the frequency at which resonance occurs ? Show Answer

Q26) The quality factor of an LCR circuit is equal to Show Answer

Q27) A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The number of turns in the secondary in order to get output at 230 V is Show Answer

Q28) In a LCR series circuit, at resonant frequency Show Answer

Q29) A choke is a : Show Answer

Q30) In an ideal parallel LC circuit, the capacitor is charged by connecting it to a dc source which is then disconnected. The current in the circuit Show Answer

Q31) In an oscillating LC circuit the maximum charge on the capacitor is Q. The charge on the capacitor when the energy stored in capacitor is twice that stored in magnetic field, is Show Answer

Q32) A resistance of 40 ohm and an inductance of 95.5 millihenry are connected in series in a 50 cycle / second AC circuit. The impedance of this combination is very nearly Show Answer

Q33) Alternating current can not be measured by DC ammeter because Show Answer

Q34) If L and R denote inductance and resistance respectively which of the following has the dimensions of frequency ? Show Answer

Q35) The average value of alternating current over one complete cycle is Show Answer

Q36) A coil of inductance 40 henry is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is Show Answer

Q37) A step-down transformer is employed to reduce the main supply of 220 V to 11 V. The primary draws 5 A of current and the secondary draws 90 A. The efficiency of the transformer is Show Answer

Q38) The resonant frequency of a circuit is f. If the capacitance is made 4 times the initial value, then the resonant frequency will become Show Answer

Q39) Large transformers, when used for sometime, become hot and are cooled by circulating oil. The heating of transformer is due to Show Answer

Q40) There is a current of 10 milliampere through an ideal choke coil when connected to 220 volt, 50 hertz supply. The power consumed is Show Answer

Q41) A device which converts electrical energy into mechanical energy is Show Answer

Q42) Energy is stored in the choke coil in the form of Show Answer

Q43) In a step-up transformer, the turns ration is 1 : 2. A Leclanche cell ( emf 1.5 V ) is connected across the primary. The voltage across the secondary is Show Answer

Q44) In a transformer, the number of turns of primary coil and secondary coil are 5 and 4 respectively. If 220 V is applied on the primary coil, then the ratio of primary current to the secondary current is Show Answer

Q45) The power factor in an AC series L-R circuit is Show Answer

Q46) The magnetic field energy in an inductor changes from maximum value to minimum value in 5.0 ms when connected to an AC source. The frequency of the source is Show Answer

Q47) The reactance of a coil, when used in the domestic AC power supply ( 220 volt, 50 cycles per second ) is 50 ohm. The inductance of the coil is nearly Show Answer

Q48) An inductor, a capacitor and a resistor are connected in series to an AC supply. When measured with an AC voltmeter, the potential difference across the inductor, capacitor and resistor are respectively 90 volt, 60 volt and 40 volt. Then the supply voltage is Show Answer

Q49) In a series resonant circuit, the AC voltages across resistance R, inductance L and capacitance C are 5 V , 10 V, 10 V respectively. The AC voltage applied to the circuit will be Show Answer

Q50) An rms current 0.6 A flows when an inductance of 40 mH is connected to an AC source of 24 V ( rms ). The angular frequency of the source is Show Answer

Q51) An inductor of 2 henry and a resistance of 10 ohm are connected in series with a battery of 5 volt. The initial rate of change of current is Show Answer

Q52) An alternating current having peak value 14 A used to heat a metal wire. To produce the same heating effect, a constant current i can be used where i is Show Answer

Q53) A dyanmo dissipates 20 watt when it supplies a current of 4 A through it. If the terminal potential difference is 220 volt, then the emf produced is Show Answer

Q54) An ideally efficient transformer has a primary power input of 10 k W. The secondary current when the transformer is on load is 25 ampere. If the primary : secondary turns ratio is 8 : 1, then the potential difference applied to the primary coil is Show Answer

Q55) Lenz's law is a consequence of the law of conservation of : Show Answer

Q56) "The induced e.m.f. is always in such a direction so as to oppose the change that causes it" is called : Show Answer

Q57) An electron moves in the line from left to right, which lies below in the plane of a circular loop of a wire (conductor). What is the direction of current induced, if any, in the loop ? Show Answer

Q58) A coil is wound on a transformer of rectangular cross-section. If all the linear dimensions of the transformer are increased by a factor 2 and number of turns per unit length of the coil remains the same, the self-induction increases by a factor of : Show Answer

Q59) A magnet is taken towards a coil and is moved (i) quickly (ii) slowly, then the induced e.m.f. is : Show Answer

Q60) In a step-up transformer : Show Answer

Q61) In a step-down transformer : Show Answer

Q62) A small transformer does not : Show Answer

Q63) A transformer has no : Show Answer

Q64) Maximum efficiency of a transformer depends : Show Answer

Q65) Auto transformer : Show Answer

Q66) Transmission of electricity is done : Show Answer

Q67) Induction furnaces work on the principle of : Show Answer

Q68) Induction motor for A.C. devices works on the principal of : Show Answer

Q69) Eddy currents do not cause : Show Answer

Q70) The role of self-inductance in a circuit is equivalent to : Show Answer

Q71) In a dead-beat galvanometer the coil is wound over a frame made of : Show Answer

Q72) A transformer has an efficiency of 80%. It works at 4 kilowatt and 100 volt. If the secondary voltage is 240 volt, then the primary and secondary currents are : Show Answer

Q73) The e.m.f. induced between the ends of an axle 1.75 meter long of a railway carriage tavelling on a level ground with a uniform speed of 54 kilometers per hour is ( vertical component of earth's field is 0.5 gauss ): Show Answer

Q74) In case of ideal step-down transformer : Show Answer

Q75) A metallic ring is attached to the wall of a room. When the north pole of a magnet is brought near the ring, the induced current in the ring is : Show Answer

Q76) Two pure inductors each of self inductance L are connected in parallel but are will separated from each other, the total inductance is : Show Answer

Q77) The back e.m.f. in a D.C. motor is maximum when the : Show Answer

Q78) Armature current in D.C. motor is maximum when the motor has : Show Answer

Q79) A bar magnet is dropped along the axis of a copper ring held horizontally. The acceleration of fall is : Show Answer

Q80) An induced e.m.f is produced when a magnet is introduced in a coil. The magnitude of this induced e.m.f. does not depend upon : Show Answer

Q81) In the electromagnetic induction, the induced e.m.f. in independent of Show Answer

Q82) Self inductance of a straight conductor is : Show Answer

Q83) If no. of turns per unit length in a solenoid is tripled, the self inductance of solenoid will Show Answer

Q84) The inductor may store energy : Show Answer

Q85) When a wire loop is rotated in a magnetic field, the direction of induced e.m.f. changes once in : Show Answer

Q86) The minimum value of inductance which can be obtained using three inductances of values 2H, 3H AND 6H is : Show Answer

Q87) If the angular speed of rotation of an armature of alternator is doubled then induced e.m.f. will be : Show Answer

Q88) The current is flowing in two co-axial coils in the same direction. On increasing the distance between the two coils, the electric current will : Show Answer

Q89) Two different loops are concentric and lie in the same plane. The current in the outer loop is clockwise and increasing with time. The induced current in the inner loop is then : Show Answer

Q90) A transformer changes : Show Answer

Q91) A copper disc of radius R is rotated about its center with frequency v in a uniform field of strength B Tesla perpendicular to its plane. The e.m.f. induced between its axle and tip of edge is : Show Answer

Q92) An electric bulb in series with a large inductor when connected across a D.C. source takes a little time before reaching a stable glow. If an iron core is inserted into the inductor the delay will Show Answer

Q93) An electric bulb of 100W is connected in parallel with an ideal inductor of 1H. The arrangement is connected to a 90 V battery through a switch. On pressing the switch. Show Answer

Q94) A wheel with 8 spokes is rotated in a plane normal to the earth's magnetic field so that an e.m.f. of 4 m V is induced between the axle and the rim of the wheel. Keeping all the other things unchanged, the number of spokes is increased to 16. Now the e.m.f. between the axle and rim of the wheel is Show Answer

Q95) A conductor having no ohmic resistance resists the flow of changing current because Show Answer

Q96) A coil of resistance R and inductance L is connected to a battery of E volts e.m.f. The current in the coil is Show Answer

Q97) A copper ring is having a cut. A bar magnet is dropped through the ring with its length along the axis of the ring. Then the acceleration of the falling magnet is Show Answer

Q98) The induced charge in an inductance is independent of : Show Answer

Q99) If the magnetic flux linked with a coil through which a current X A is flowing is Y Wb, then coefficient of self induction is : Show Answer

Q100) A small loop of wire of side (l) is placed inside a large square loop of wire of side (L) (L > > l). The loops are coplanar and their centers coincide. The mutual induction of the system is proportional to Show Answer

Q101) Quantity that remains unchanged in a transformer is Show Answer

Q102) The direction of induced current is such that it opposes the very cause that produces it. This is the law of Show Answer

Q103) The unit of inductance is equivalent to Show Answer

Q104) A long metallic rod (horizontal) with length along the east west direction is falling freely under gravity. The potential difference between its ends will Show Answer

Q105) A Cu-ring is suspended by a thread in a vertical plane. The north pole of a magnet is moved horizontally towards the ring along the axis of the ring. The ring will Show Answer

Q106) A disc of 10.0 cm diameter is rotated at a speed of 3600 r.p.m. inside a long solenoid of 1200 turns per meter on the axis of the solenoid and perpendicular to the plane of the disc. When a current of 1.5 A is passed through the solenoid, the difference in the potential between the axis and circumference of the disc is nearly Show Answer

Q107) A.C. which we use in houses has peak value of nearly : Show Answer

Q108) When two mutually perpendicular alternating magnetic fields superimpose on each other, the resulting field is : Show Answer

Q109) In a D.C. motors, the current flowing through the armature is minimum when induced e.m.f. is : Show Answer

Q110) For 100% efficiency of D.C. motor, the applied potential should be : Show Answer

Q111) The approximate formula expressing the mutual inductance of two thin co-axial loops of the same radius 'a' when their centres are separated by a distance l, with l > > a is : Show Answer

Q112) Find the inductance of a solenoid of length l whose winding is made of copper wire of mass m. The winding resistance is equal to R. The solenoid diameter is considerably less than its length. Show Answer

Q113) In an A.C. circuit, at resonance the phase difference between current and voltage is : Show Answer

Q114) At resonance the power factor of L-C-R circuit is : Show Answer

Q115) The power factor in a circuit connected at a A.C. power supply has a value which is : Show Answer

Q116) Using an A.C. voltmeter the potential difference in the electrical line in a house is read to be 234 volts. If the line frequency is known to be 50 cycles/seconds, the equation for the line voltage V is : Show Answer

Q117) Ohm's law expressed as E= IR Show Answer

Q118) The speed of fan is reduced by putting a rheostat in series with the fan, we consume: Show Answer

Q119) A choke and capacitor are connected in series and current is maximum when input frequency is f. If they are put in parallel, the current is maximum at frequency : Show Answer

Q120) In L-C-R circuit, the value of capacitance is doubled. For the resonant frequency to remain the same, the inductance should be changed from L to : Show Answer

Q121) 220 V a.c. is more dangerous than 220 V d.c. because : Show Answer

Q122) L and R denote inductance and resistance. The dimensions of L/R is : Show Answer

Q123) The time taken for a current to attain the maximum value in d.c. circuit containing 'L' and R depends upon : Show Answer

Q124) An L-C-R circuit is connected to source a.c. At resonance , the phase difference between voltage and current in the circuit is : Show Answer

Q125) Two cables of copper are of equal lengths. One of them has single wire of area A an the other has 10 wires each of cross-section A/10 each. Given their suitability for transporting a.c. and d.c. Show Answer

Q126) A choke coil may be used as a resistance in : Show Answer

Q127) The current in the a.c. circuit measures 5 A. Its maximum instantaneous magnitude will be : Show Answer

Q128) The parallel L-C circuit acts as a simple harmonic oscillator due to exchange of : Show Answer

Q129) In series L-C-R circuit at resonance, the voltage across the inductance is : Show Answer

Q130) A lamp which can carry a current of 10 A at 15 V is connected to an a.c. source of 220 V, 50 Hz, the inductance of choke coil needed to light the lamp is : Show Answer

Q131) An altering current in series LCR circuits is maximum if: Show Answer

Q132) Same current flowing in two a.c. circuits. The first contains only inductance and second contains only capacitance. If the frequency of e.m.f. of a.c. is increased for both, the effect on the current will be : Show Answer

Q133) The value of form factor for altering current is : Show Answer

Q134) With fluorescent tube in A.C. circuit, we connect: Show Answer

Q135) A 220 volt input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volt. If the efficiency of the transformer is 80% , the current drawn by the primary windings of the transformer is : Show Answer

Q136) A real capacitor can be represented in terms of ideal components as: Show Answer

Q137) A real inductor can be represented as : Show Answer

Q138) An a.c. virtual voltage of 100 virtual volts is applied to a circuit of resistance of 0.5 ohm and inductance 0.01 H, the frequency being 50 Hz. The lag in time in voltage and current is : Show Answer

Q139) When we touch the terminal of a high voltage capacitor, even after a high voltage has been cut off. Then the capacitor has the tendency to : Show Answer

Q140) The number of turns in the primary coil of a transformer is 200 and the number of turns in the secondary coil 10. If 240 volt A.C. is applied to the primary, the output from the secondary will be : Show Answer

Q141) The coil of a choke in a circuit : Show Answer

Q142) The reactance of coil when used in the A.C. power supply ( 220 volt, 50 cycles /s) is 50 ohms. The inductance of the coil is nearly : Show Answer

Q143) Impedance of circuit when a resistance R and a inductor of inductance L are connected in series in an A.C.circuit of frequency v, is : Show Answer

Q144) The ratio of the induced e.m.f. in a coil having 50 turns and rotating with 50 Hz to that of the induced e.m.f. in a coil having 100 turns and rotating with 150 Hz in the same magnetic field is : Show Answer

Q145) 220 V, 50Hz A.C. source is connected to inductance of 0.2 H and a resistance of 20 ohm in series. What is the current in the circuit : Show Answer

Q146) A Lechlanche Cell of e.m.f. 1.4 V is connected to the primary of a tranformer of turn ratio 10:1. The output voltage is : Show Answer

Q147) The coefficient of self inductance of a coil is given by : Show Answer

Q148) A transformer is used to light 140 watt, 24 volt lamp from 240 volts A.C. mains. If the current in the mains is 0.7 A, then the efficiency of transformer is : Show Answer

Q149) Which of the following is correct ? Show Answer

Q150) A short-circuited coil is placed in a time varying magnetic field. Electrical power is dissipated due to to the current induced in the coil. If no. of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be : Show Answer

Q151) In an ideal parallel LC-circuit, the capacitor is charged by connecting it to a d.c. source which is then disconnected. The current in the circuit : Show Answer

Q152) Electric fan works on the principle of : Show Answer

Q153) A horizontal straight conductor when placed along south north direction falls under gravity there is : Show Answer

Q154) The r.m.s. value of an A.C. of 50 Hz is 10 A. The time taken by an alternating current in reaching from zero to maximum value and the peak value will be : Show Answer

Q155) In a LCR series circuit, at resonant frequency : Show Answer

Q156) Eddy currents are produced in : Show Answer

Q157) Which law follows the law of conservation of energy ? Show Answer

Q158) A lamp of same rating is used to a 200 V d.c. and a 200 V a.c. supply. The lamp will : Show Answer

Q159) In an induction coil, the coefficient of mutual inductance is 4 henry. If a current of 5 A in the primary coil is cut off in 1/1500s, the e.m.f. at the terminals of the secondary coil will be: Show Answer

Q160) The self inductance of a solenoid of length L, the area of cross section A and having N turns is : Show Answer

Q161) A e.m.f. of 100 millivolt is induced in a coil when the current in another nearby coil becomes 10 A from zero in 0.1 second. The coefficient of mutual induction between the two coils will be ? Show Answer

Q162) A 100 mH coil carries a current of 10 A. The magnetic energy stored in the coil is Show Answer

Q163) The capacitance is made 1/4th in an LCR circuit, then how much should the inductance be changed so that the circuit remains in resonance : Show Answer

Q164) The ratio of turns of transformer is 2:3. Given that the current through the primary is 3 A, then what is the current through the load resistance : Show Answer

Q165) What is the equivalent inductance of a system of two inductors L joined in parallel : Show Answer

Q166) One henry is equal to Show Answer

Q167) A transformer with efficiency 80% works at 4 kW and 100 V. If the secondary voltage is 200 V, then the primary and secondary currents are respectively : Show Answer

Q168) A metallic ring is dropped down, keeping its plane perpendicular to a constant and horizontal magnetic field. The ring enters the region of magnetic field at t = 0 and completely emerges out at t = T sec. The current in the ring varies as : Show Answer

Q169) Two coil of self inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between those coils is : Show Answer

Q170) The core of a transformer is laminated because: Show Answer

Q171) A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 amp, the efficiency of the transformer is approximately : Show Answer

Q172) A conducting circular loop is placed in a uniform magnetic field 0.04 T with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at 2 mm /s. The induced e.m.f. in the loop when the radius is 2 cm is : Show Answer

Q173) A loss free transformer has 500 turns in the primary and 2500 in secondary. The meters of the secondary are indicating 200 volts, 18 ampere. Under these conditions, what would be the meters of the primary read ? Show Answer

Q174) If applied voltage on a motor is 200 volt and back e.m.f is 100 volt the efficiency of the motor is Show Answer

Q175) It is desired to send an altering current 5 sin 400 t through a solenoid that has a self inductance of 3 mH. If the resistance of the solenoid is assumed to be negligible, the voltage impressed across the solenoid terminals to provide this current is : Show Answer

Q176) With the increase in frequency of an a.c. supply, the impedance of an L-C-R series circuit Show Answer

Q177) An artificial satellite with a metal surface is moving about the earth in a circular orbit. A current will be induced in the satellite if Show Answer

Q178) A conducting rod is moving with velocity v in a magnetic field B. An induced e.m.f. will be generated between its two ends if Show Answer

Q179) The coefficient of self-induction of two coils are 0.01 H and 0.03 H respectively. If they oppose each other then the resultant self induction will be, if M = 0.01 H Show Answer

Q180) A current time curve is shown in the following diagram. This type of current is passed in the primary coil of a transformer. The nature of induced e.m.f. in the secondary coil will be : Show Answer

Q181) The dimensions of the quantity L/CVR are equivalent to those of : Show Answer

Q182) A cycle wheel with 64 spokes is rotating with N rotations per second at right angles to horizontal component of magnetic field. The induced e.m.f. generated between its axle and rim is E. If the number of spokes is reduced to 32 then the value of induced e.m.f. will be : Show Answer

Q183) Same current is flowing in two identical coaxial circular coils. On looking the coils from a point at the center between them, the current in one coil appears to be flowing in clockwise direction. If the two coils are displaced towards each other then the value of current Show Answer

Q184) The phase difference between the flux linked with a coil rotating in a uniform magnetic field and induced e.m.f. produced in it is Show Answer

Q185) If the capacity of a condenser is 1 farad then its resistance in a D.C. circuit will be Show Answer

Q186) The values of alternating current and alternating e.m.f. for a resistance less choke coil are 1 A and 220 volt respectively. The power loss in the circuit will be : Show Answer

Q187) A bulb and a condenser are connected in series with an A.C. source. On increasing the frequency of the source its brightness will : Show Answer

Q188) The constant speed of the frame is Show Answer

Q189) The emf induced in the loop is Show Answer

Q190) The potential difference between the points a and b is equal to Show Answer

Q191) Which of the following represents the current generated by the apparatus Show Answer

Q192) An increase in which of the following parameters would not increase the current generated by the apparatus, Show Answer

Q193) What will be the direction of current in the apparatus shown ? Show Answer

Q194) Statement 1 : Induced e.m.f in an inductor may be non-zero, even if the current through it is zero.
Statement 2 : For alternating sinusoidal current passing through an inductor, voltage across inductor and current are completely out of phase.
Show Answer

Q195) The voltage drop across the resistor is given as Show Answer

Q196) The resistance of the coil is Show Answer

Q197) The voltage drop across the coil is Show Answer

Q198) The device X can be Show Answer

Q199) Let the two devices have same resistance. The voltage across the series combination is V an current is i. Select the current alternative Show Answer

Q200) The device Y cannot be Show Answer

Q201) Induced emf in the coil depends upon Show Answer

Q202) A step-down transformer reduces the voltage of a transmission line from 2200 V to 220 V. The power delivered by it is 880 W and its efficiency is 88%. The input current is Show Answer

Q203) Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 ampere in 0.006 second in the primary will be Show Answer

Q204) A circular coil and a bar magnet placed near by are made to move in the same direction. The coil covers a distance of 1 m in 0.5 sec and the magnet a distance of 2m in 1 sec. The induced emf produced in the coil Show Answer

Q205) A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis, then Show Answer

Q206) When power is drawn from the secondary coil of the transformer, the dynamic resistance Show Answer

Q207) Current in a coil changes from 5 A to 10 A in 0.2 s. If the coefficient of self-induction is 10 H, then the induced emf is Show Answer

Q208) If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become Show Answer

Q209) The particle accelerator that uses the phenomenon of electromagnetic induction is the Show Answer

Q210) In a transformer 220 ac voltage is increased to 2200 volts. If the number of turns in the secondary are 2000, then the number of turns in the primary will be Show Answer

Q211) The coils of a step down transformer have 500 and 5000 turns. In the primary coil an ac of 4 ampere at 2200 volts is sent. The value of the current and potential difference in the secondary coil will be Show Answer

Q212) When a battery is connected across a series combination of self inductance L and
Resistance R, the variation in the current i with time t is best represented by Show Answer

Q213) The self inductance of a coil is 5 henry, a current of 1 amp change to 2 amp within 5 second through the coil. The value of induced e.m.f. will be Show Answer

Q214) An infinitely cylinder is kept parallel to an uniform magnetic field B directed along positive z axis. This direction of induced current as seen from the z axis will be Show Answer

Q215) The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following conditions is correct Show Answer

Q216) Which type of losses donot occur in the transformer? Show Answer

Q217) There is a uniform magnetic field directed perpendicular and into the plane of the paper. An irregular shaped conducting loop is slowly changing into a circular loop in the plane of the paper. Then Show Answer

Q218) When the current changes from +2 A to -2 A in 0.05 s, an emf of 8 V is induced in a coil. The coefficient of self-induction of the coil is Show Answer

Q219) A transformer rated at 10k W is used to connect a 5 kV transmission line to a 240 V circuit. The ratio of turns in the windings of the transformer is Show Answer

Q220) A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then Show Answer

Q221) The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was Show Answer

Q222) Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon Show Answer

Q223) The current is flowing in two coaxial coils in the same direction. On increasing the distance between the two, the electric current will Show Answer

Q224) According to phenomenon of mutual inductance Show Answer

Q225) If a copper ring is moved quickly towards south pole of a powerful stationary bar magnet, then Show Answer

Q226) The self-inductance of the motor of an electric fan is 10 H. In order to impart maximum power at 50 Hz, it should be connected to a capacitance of Show Answer

Q227) When a bar magnet falls through a long hollow metal cylinder fixed with its axis vertical, the final acceleration of the magnet is Show Answer

Q228) If the current is halved in a coil, then the energy stored is how much times the previous value Show Answer

Q229) A 50 mH coil carries a current of 2 A, the energy stored in joule is Show Answer

Q230) Which of the following phenomena is utilised in the construction of mouth piece of a telephone now a days? Show Answer

Q231) The north pole of a long horizontal bar magnet is being brought closer to a vertical conducting plane along the perpendicular direction. The direction of the induced current in the conducting plane will be Show Answer

Q232) Armature current in dc motor will be maximum when Show Answer

Q233) A short-circulated coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electrical power dissipated would be Show Answer

Q234) In a dc motor, induced e.m.f. will be maximum Show Answer

Q235) In an A.C. generator, when the plane of the armature is perpendicular to the magnetic field Show Answer

Q236) For a large industrial city with much load variations the DC generator should be Show Answer

Q237) Lenz’s law is statement of Show Answer

Q238) Faraday’s laws are consequence of conservation of Show Answer

Q239) Turn ratio is 1.25. The step up transformer operates at 230 V and current through secondary is 2 A. Then current in primary is Show Answer

Q240) The square root of the product of inductance and capacitance has the dimension of Show Answer

Q241) An electric motor runs a DC source of emf 200V and draws a current of 10A. If the efficiency is 40%, then the resistance of the armature is Show Answer

Q242) What should be the value of self inductance of an inductor that should be connected to 220 V, 50 Hz supply so that a maximum current of 0.9 A flows through it? Show Answer

Q243) A magnet is brought towards a coil (i) speedly (ii) slowly, then the induced e.m.f/induced charge will be respectively Show Answer

Q244) When a metallic plate swings between the poles of magnet Show Answer

Q245) When a wire loop is rotated in a magnetic field, the direction of induced e.m.f. changes one in each Show Answer

Q246) A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately Show Answer

Q247) The net magnetic flux through any closed surface, kept in a magnetic field is Show Answer

Q248) Whenever a magnet is moved either towards or away from a conducting coil, an emf is induced, the magnitude of which is independent of Show Answer

Q249) When the number of turns and the length of the solenoid are doubled keeping the area of cross-section same, the inductance Show Answer

Q250) The total charge, induced in a conducting loop, when it is moved in a magnetic field depends on Show Answer

Q251) A magnet is dropped down an infinitely long vertical copper tube Show Answer

Q252) A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be Show Answer

Q253) The number of turns in primary and secondary coils of a transformer are 100 and 20 respectively. If an alternating potential of 200 volt is applied to the primary, the induced potential in secondary will be Show Answer

Q254) Fleming’s left and right hand rule are used in Show Answer

Q255) What is increased in step-down transformer Show Answer

Q256) In a coil when current changes from 10A to 2A in time 0.1s, induced emf is 3.28 V. what is self –inductance of coil? Show Answer

Q257) An e.m.f. of 12 volt is produced in a coil when the current in it changes at the rate of 45 amp/minute. The inductance of the coil is Show Answer

Q258) A transformer is employed to Show Answer

Q259) A 220-volt input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is Show Answer

Q260) According to Lenz’s law of electromagnetic induction Show Answer

Q261) A long horizontal metallic rod with length along the east-west direction is falling under gravity. The potential difference between its two ends will Show Answer

Q262) Which of the following is constructed on the principle of electromagnetic induction Show Answer

Q263) If a coil of metal wire is kept stationary in a non-uniform magnetic field, then Show Answer

Q264) Energy associated with a moving charge is due to Show Answer

Q265) The induction coil works on the principle of Show Answer

Q266) Electric fields induced by changing magnetic fields are Show Answer

Q267) When a circular coil of radius 1 m and 100 turns is rotated in a horizontal uniform magnetic field, the peak value of emf induced is 100 V. the coil is unwound and then rewound into a circular coil of radius 2 m. If it is rotated now, with the same speed, under similar conditions, the new peak value of emf developed is Show Answer

Q268) The number of turns in primary and secondary coils of a transformer is 50 and 200 respectively. If the current in the secondary coil is 4A, then the current in the secondary coil is Show Answer

Q269) A six pole generator with fixed field excitation developes an emf of 100 V, when operating at 1500 rpm. At what speed must it rotate to develop 120 V? Show Answer

Q270) A solenoid 60 mm long has 50 turns on it and is wound on an iron rod of 7.5 mm radius. Find the flux through the solenoid when the current in it is 3A. The relative permeability of iron is 600 Show Answer

Q271) An inductor having coefficient of self induction 40mH. What is the energy stored in it when a current of 2 A is passed through it? Show Answer

Q272) When the current through a solenoid increases at a constant rate, the induced current Show Answer

Q273) The turn ratio of a transformer is 1:2. An electrolytic DC cell of emf 2 V is connected to its primary. The output voltage across transformer is Show Answer

Q274) The north pole of a magnet is brought near a metallic ring. The direction of the induced current in the ring will be Show Answer

Q275) Self induction of a solenoid is Show Answer

Q276) Which of the following figure correctly depicts the Lenz’s law. The arrows show the movement of the labelled pole of a bar magnet into a closed circular loop and the arrows on the circle show the direction of the induced current Show Answer

Q277) A transformer has an efficiency of 80%. It is connected to a power input of 5kW at 200 V. If the secondary voltage is 250 V, the primary and secondary currents are respectively Show Answer

Q278) Lenz’s law of electromagnetic induction corresponds to the Show Answer

Q279) A circular coil has 500 turns of wire and its radius is 5 cm. The self inductance of the coil is Show Answer

Q280) A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 amp, then the current in the primary coil is Show Answer

Q281) Two similar circular loops carry equal currents in the same direction. On moving coils further apart, the electric current will Show Answer

Q282) If the number of turns in a coil becomes doubled, then it self inductance will be Show Answer

Q283) A current of 5 A is flowing at 220 V in the primary coil of a transformer. If the voltage produced in the secondary coil is 2200 V and 50% of power is lost, then the current in secondary will be Show Answer

Q284) The energy stored in an inductor of self inductance L henry carrying a current of 1 A is Show Answer

Q285) The current passing through a choke coil of 5 henry is decreasing at the rate of 2 ampere/sec. The e.m.f. developing across the coil is Show Answer

Q286) A solenoid is placed inside another solenoid, the length of both being equal carrying same magnitude of current. The parameters like radius and number of turns are in the ratio 1 : 2 for the two solenoids. The mutual inductance on each other would be Show Answer

Q287) The number of turns in primary coil of a transformer is 20 and the number of turns in the secondary is 10. If the voltage across the primary is 220 V, what is the voltage across the secondary? Show Answer

Q288) A short solenoid of length 4 cm, radius 2 cm and 100 turns is placed inside and on the axis of a long solenoid of length 80 cm and 1500 turns. A current of 3 A flows through the short solenoid. The mutual inductance of two solenoids is Show Answer

Q289) When the speed of a dc motor increases the armature current Show Answer

Q290) A generator at a utility company produces 100 A of current at 4000 V. The voltage is stepped up to 240000 V by a transformer before it is sent on a high voltage transmission line. The current in transmission line is Show Answer

Q291) In a step-up transformer, the turn ratio is 1 : 2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary. The voltage developed in the secondary would be Show Answer

Q292) For previous objective, which of the following graphs is correct Show Answer

Q293) Two different loops are concentric and lie in the same plane. The current in the outer loop is clockwise and increasing with time. The induced current in the inner loop then, is Show Answer

Q294) An inductor is connected to an AC source. When compared to voltage , the current in the lead wires Show Answer

Q295) In an AC series circuit, the instantaneous current is maximum when the instantaneous voltage is maximum. The circuit element connected to the source will be Show Answer

Q296) What is self inductance of a coil which produces 5V, when current in it changes from 3 A to 2 A in one millisecond? Show Answer

Q297) An electric bulb has a rated power of 50 W at 100 V. If it is used on an AC source 200 V, 50 Hz, a choke has
to be used in series with it. The should have an inductance of Show Answer

Q298) A magnet is suspended lengthwise from a spring and while it oscillates, the magnet moves in and out of the coil C connected to a galvanometer G. Then as the magnet oscillates. Show Answer

Q299) A transformer is having 2100 turns in primary and 4200 turns in secondary. An AC source of 120 V, 10 A is connected to its primary. The secondary voltage and current are Show Answer

Q300) In an L-C-R series AC circuit the voltage across L, C and R is 10 V each. If the inductor is short circuited, the
voltage across the capacitor would become Show Answer

Q301) 24. A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary coil has 75 turns, the number of turns in the secondary coil is Show Answer

Q302) Which of the following quantities remains constant in a step-down transformer ? Show Answer

Q303) What is the self-inductance of a coil which produces 5 V when the current changes from 3 A to 2 A in one millisecond? Show Answer

Q304) The power factor of good choke coil is Show Answer

Q305) In Colpitt oscillator the feedback network consists of Show Answer

Q306) A current of 10 A in the primary coil of a circuit is reduced to zero. If the coefficient f mutual inductance is 3H and emf induced in secondary coil is 30 kV, time taken for the change of current is Show Answer

Q307) In an ideal transformer, the voltage is stepped down from 11 kV to 220 V. If the primary current be 100 A, the current in the secondary should be Show Answer

Q308) If the capacity of a condenser is 1 F, then its resistance in a DC circuit will be Show Answer

Q309) For a large industrial city with much load variations , the DC generator should be Show Answer

Q310) A circuit draws 330 W from a 110V, 60 Hz AC line. The power factor is 0.6 and the current lags the voltage.
The capacitance of a series capacitor that will result in a power factor of unity is equal to Show Answer

Q311) The primary winding of a transformer has 200 turns and its secondary winding has 50 turns. If the current
in the secondary winding is 40 A, the current in the primary is Show Answer

Q312) An electric heater rated 220 V and 550 W is connected to A.C. mains. The current drawn by it is Show Answer

Q313) If the coils of a transformer are made up of thick wire, then Show Answer

Q314) At high frequency, the capacitor offer Show Answer

Q315) A resistor and a capacitor are connected in series with an AC source. If the potential drop across the capacitor is 5 V and that across resistor is 12 V, then applied voltage is Show Answer

Q316) The ratio of turns in primary and secondary coils of a transformer is 1 : 20. The ratio of currents in primary and secondary coils will be
Show Answer

Q317) If number of turns in primary and secondary coils is increased to two times each, the mutual inductance Show Answer

Q318) An ideal choke draws a current of 8 A when connected to an AC supply of 100 V, 50 Hz. A pure resistor draws a current of 10 A when connected to the same source. The ideal choke and the resister are connected in series and then connected to the AC source of 150 V, 40 Hz. The current in the circuit becomes Show Answer

Q319) 101. A bulb is connected first with dc and then ac of same voltage it will shine brightly with Show Answer

Q320) The maximum value of AC voltage in a circuit is 707 V. Its rms value is Show Answer

Q321) A transformer is used to light 140 W, 24 V lamp from 240 V AC mains. The current in the mains is 0.7 A.
The efficiency of transformer is nearest to Show Answer

Q322) Eddy current are produced when Show Answer

Q323) Alternating current cannot be measured by DC ammeter because Show Answer

Q324) The number of turns in the primary coil of a transformer is 200 and the number of turns in secondary coil
is 10. If 240 V AC is applied to the primary, the output from secondary will be Show Answer

Q325) The time taken by AC of 50 Hz in reaching from zero to the maximum value is Show Answer

Q326) A bulb and a capacitor are in series with an ac source. On increasing frequency how will glow of the bulb
change
Show Answer

Q327) The time taken by an alternating current of 50 Hz in reaching from zero to its maximum value will be Show Answer

Q328) In a current carrying long solenoid, the field produced does not depend upon Show Answer

Q329) Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the emf of AC is increased, the effect on the value of the current Show Answer

Q330) The number of turns of primary and secondary coils of a transformer is 5 and 10 respectively and mutual inductance of the transformer is 25 H. Now, number of turns in primary and secondary are made 10 and 5 respectively. Mutual inductance of transformer will be Show Answer

Q331) The armature of a shunt wound motor can with stand current up to 8A before it overheats and it damaged. If the armature resistance is 0.5 Ω, minimum back emf that must be motor is connected to a 120 V line is Show Answer

Q332) During a current change from 2 A to 4 A in 0.05 s, 8 V of emf is developed in a coil. The coefficient of self-
induction is Show Answer

Q333) Find the time required for a 50 Hz alternating current to become its value from zero to the rms value Show Answer

Q334) A pure inductive coil of 30 mH is connected to an AC source of 220 V, 50 Hz. The rms current in the coil is Show Answer

Q335) A coil of wire of certain radius has 100 turns and a self inductance of 15 mH. The self inductance of a
second similar coil of 500 turns will be Show Answer

Q336) A telephone wire of length 200 km has a capacitance of 0.014 μF per km. If it carries an AC frequency 5
kHz, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum? Show Answer

Q337) An air cored coil has a self-inductance of 0.1 H. A soft iron core of relative permeability 100 is 1/10 th. The value of self-inductance now becomes Show Answer

Q338) When the rate of change of current is unity, induced emf is equal to Show Answer

Q339) The induced emf of a generator when the flux of poles is doubled and speed is doubled Show Answer

Q340) In the non-resonant circuit, what will be the nature of the circuit for frequencies higher than the resonant
frequency Show Answer

Q341) 220 V, 50 Hz AC is applied to a resistor. The instantaneous value of voltage is Show Answer

Q342) Current in the LCR circuit becomes extremely large when Show Answer

Q343) Which of the following statement is incorrect? Show Answer

Q344) A capacitor and an inductance coil are connected in separate AC circuits with a bulb glowing in both the
circuits. The bulb glows more brightly when Show Answer

Q345) A coil of inductance 0.2 H and 1.0 W resistance is connected to a 90 V source. At what rate will the current in the coil grow at the instant the coil is connected to the source? Show Answer

Q346) Consider a short magnetic dipole of magnetic length 10 cm. Its geometric length is Show Answer

Q347) If coefficient of self induction of a coil is 1 H, an emf of 1 V is induced, if Show Answer

Q348) The power loss in AC circuit will be minimum when Show Answer

Q349) What is the average power dissipation in an ideal capacitor in AC circuit? Show Answer

Q350) An inductance 1 H is connected in series with an AC source of 220 V and 50 Hz. The inductive reactance (in ohm) is Show Answer

Q351) The maximum voltage in DC circuit is 282V. The effective voltage in AC circuit will be Show Answer

Q352) An irregular closed loop carrying a current has a shape such that the entire loop cannot lie in a single plane. If this is placed in a uniform magnetic field, the force acting on the loop Show Answer

Q353) A 50 V AC is applied across an R-C (series) network. The rms voltage across the resistance is 40 V, then the potential across the capacitance would be
Show Answer

Q354) The number of turns in a secondary coil is twice the number of turns in primary. A leclanche cell of 1.5 V is connected across the primary. The voltage across secondary is Show Answer

Q355) Q-factor can be increased by having a coil of Show Answer

Q356) What will be the phase difference between virtual voltage and virtual current, when the current in the
circuit is wattles Show Answer

Q357) Average power generated in an inductor connected to an AC source is Show Answer

Q358) When current in a coil changes from 2 A to 4 A in 0.05s, an emf of 8 V is induced in the coil. Self inductance of the coil is Show Answer

Q359) A coil has resistance 30 ohm and inductive reactance 20 Ohm at 50 Hz frequency. If ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be Show Answer

Q360) The current which does not contribute to the power consumed in an AC circuit is called Show Answer

Q361) In a circuit containing an inductance of zero resistance, the e.m.f. of the applied ac voltage leads the current by Show Answer

Q362) The peak value of an alternating current is 5 A and its frequency is 60 Hz. Find its rms value and time
taken to reach the peak value of current starting from zero. Show Answer

Q363) If a current of 3 A flowing in the primary coil is reduced to zero in 0.001 s, the induced emf in between the
two coils is 15000 V, the coefficient of mutual induction is Show Answer

Q364) A low-loss transformer has 230 V applied to the primary and gives 4.6 V in the secondary. Secondary is
connected to a load, which draws 5 A of current. The current (in ampere) in the primary is Show Answer

Q365) The resistance of a coil for dc is in ohms. In ac, the resistance Show Answer

Q366) If 25 A current is drawn by 220 V motor and back emf produced is 80 V, the value of armature resistance is Show Answer

Q367) Two circuits have mutual inductance of 0.09 H. Average emf induced in the secondary by a change of current from 0 to 20 A in 0.006 s in primary will be Show Answer

Q368) Mutual inductance of two coils can be increased by Show Answer

Q369) A coil is wound on a core of rectangular cross-section. If all the linear dimensions of core are increased by
a factor 2 and number of turns per unit length of coil remains same, the self-inductance increases by a factor of Show Answer

Q370) A choke is preferred to a resistance for limiting current in AC circuit because Show Answer

Q371) The induced emf can be produced in a coil by
A. moving the coil with uniform speed inside uniform magnetic field
B. moving the coil with non uniform speed inside uniform magnetic field
C. rotating the coil inside the uniform magnetic field
D. changing the area of the coil inside the uniform magnetic field
Choose the correct answer from the options given below:
Show Answer

Q372) A coil is placed in a time varying magnetic field. If the number of turns in the coil were to be halved and the radius of wire is doubled, the electrical power dissipated due to the current induced in the coil would be
(Assume the coil to be shorted circuited)
Show Answer

Q373) A planar loop of wire rotates in a uniform magnetic field. Initially at t=0, the plane of the loop is
an perpendicular to the magnetic field. If it rotates with a period of 10 s about an axis in its plane, then the magnitude of induced emf will be maximum and minimum respectively at
Show Answer

Q374) At the centre of a fixed large circular coil of radius R, a much smaller circular coil of radius r is placed. The two coils are concentric and are in the same plane. The larger coil carries a current I. The smaller coil is 1800s set to rotate with a constant angular velocity @ about an axis along their common diameter. Calculate the emf induced in the smaller coil after a time t of its start of rotation. Show Answer

Q375) A circular loop of radius 0.3 cm lies parallel to a much bigger circular loop of radius 20 cm. The centre of the small loop is on the axis of the bigger loop. The distance between their centres is 15 cm. If a current of 2.0 A flows through the smaller loop, then the flux linked with bigger loop is Show Answer

Q376) A coil is suspended in a uniform magnetic field with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil, it starts oscillating; it is very difficult to stop. But, if an aluminium plate is placed near to the coil, it stops. This is due to Show Answer

Q377) An emf of 0.08 V is induced in a metal rod of length 10 cm held normal to a uniform magnetic field of 0.4 T, when moves with a velocity of Show Answer

Q378) Given below are two statements, One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) A bar magnet dropped through a metallic cylindrical pipe takes more time to come down compared to a non-magnetic bar with same geometry and mass.
Reason (R) For the magnetic bar, Eddy currents are produced in the metallic pipe which oppose motion of the magnetic bar.com idi a rubian In the light of the above statements, choose the most appropriate answer from the options given below. Show Answer

Q379) A wire of length 1 m moving with velocity 8 m/s at right angles to a magnetic field of 27. The magnitude of induced emf between the ends of wire will be Show Answer

Q380) A conducting circular loop is placed in a uniform magnetic field of 0.4 T with its plane perpendicular to the field. Somehow, the radius of the loop starts expanding at a constant rate of 1 mm/s. The magnitude of induced emf in the loop at an instant when the radius of the loop is 2 cm will be ....... μ V. Show Answer

Q381) A 12 V battery connected to a coil of resistance 6Ω through a switch, drives a constant current in the circuit. The switch is opened in 1 ms. The emf induced across the coil is 20 V. The inductance of the coil is Show Answer

Q382) The time taken for the magnetic energy to reach 25% of its maximum value, when a solenoid of resistance R, inductance L is connected to a battery, is Show Answer

Q383) An inductor coil stores 64 J of magnetic field energy and dissipates energy at the rate of 640 W when a current of 8 A is passed through it. If this coil is joined across an ideal battery, find the time constant of the circuit in seconds.) Show Answer

Q384) A series L-R circuit is connected to a battery of emf V. If the circuit is switched on at t=0, then the time at which the energy stored in the inductor reaches (1/n) times of its maximum value, is Show Answer

Q385) The self-induced emf of a coil is 25 V. When the current in it is changed at uniform rate from 10 A to 25 A in 1s, the change in the energy of the inductance is Show Answer

Q386) Two coils are placed close to each other. The mutual inductance of the pair of coils depends on Show Answer

Q387) A coil of inductance 2 H having negligible resistance is connected to a source of supply whose voltage is given by V = 3t V (where, t is in second). If the voltage is applied when t=0, then the energy stored in the coil after 4 s is .... J Show Answer

Q388) In a fluorescent lamp choke (a small transformer), 100 V of reverse voltage is produced when the choke current changes uniformly from 0.25A to 0 in a duration of 0.025 ms. The self-inductance of the choke (in mH) is estimated to be Show Answer

Q389) Given below are two statements Statement I When the frequency of an AC source in a series L-C-R circuit increases, the current in the circuit first increases, attains a maximum value and then decreases.
Statement II In a series L-C-R circuit, the value of power factor at resonance is one.
In the light of the above statements, choose the most appropriate answer from the options given below.
Show Answer

Q390) Given below are two statements
Statement I Maximum power is dissipated in a circuit containing an inductor, a capacitor and a resistor connected in series with an AC source, when resonance occurs
Statement II Maximum power is dissipated in a circuit containing pure resistor due to zero phase difference between current and voltage. In the light of the above statements, choose the correct answer from the options given below:
Show Answer

Q391) Given below are two statements
Statement I An AC circuit undergoes electrical resonance if it contains either a capacitor or an inductor.
Statement II An AC circuit containing a pure capacitor or a pure inductor consumes higher power due to its non-zero power factor.
In the light of the above statements, choose the no correct answer from the options given below.
Show Answer

Q392) When you walk through a metal detector carrying a metal object in your pocket, it raises an alarm. This phenomenon works on Show Answer

Q393) To increase the resonant frequency in series L-C-R circuit, Show Answer

Q394) If wattless current flows in the AC circuit, then the
circuit is
Show Answer

Q395) Given below are two statements.
Statement I The reactance of an AC circuit is zero. It is possible that the circuit contains a capacitor and an inductor.
Statement II In AC circuit, the average power delivered by the source never becomes zero. In the light of the above statements, choose the correct option. Show Answer

Q396) In a series L-C-R resonance circuit, if we change the resistance only, from a lower to higher value, Show Answer

Q397) An AC source rated 220 V, 50 Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is Show Answer

Q398) What happens to the inductive reactance and the current in a purely inductive circuit, if the frequency is halved? Show Answer

Q399) An AC circuit has R = 100 Q, C = 2 μF and
L=80 mH connected in series. The quality factor of the circuit is
Show Answer

Q400) An L-C-R circuit behaves like a damped harmonic oscillator. Comparing it with a physical spring-mass damped oscillator having damping constant b, the correct equivalence would be Show Answer

Q401) In an L-C-R circuit, capacitance is changed from C to 2C. For the resonant frequency to remains unchanged, the inductance should be changed from L to
Show Answer

Q402) In a series L-C-R resonant circuit, the quality factor is measured as 100. If the inductance is increased by two fold and resistance is decreased by two fold, then the quality factor after this change will be Show Answer

Q403) A capacitor of capacitance 500μF is charged completely usinga de supply of 100 V. It is now connected to an inductor of inductance 50 mH to form an L-C circuit. The maximum current in L-C circuit will be ............ A. Show Answer

Q404) A transformer operating at primary voltage 8 kV and secondary voltage 160 V serves a load of 80 kW. Assuming the transformer to be ideal with purely 60 resistive load and working on unit power factor, the A loads in the primary and secondary circuits would be Show Answer

Q405) A power transmission line feeds input power at 2300 V to a step-down transformer with its primary is windings having 4000 turns. The output power delivered at 230 V by the transformer. If the current in the primary of the transformer is 5A and its efficiency is 90%, the output current would be Show Answer

Q406) In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency o in a magnetic field B. The maximum value of emf generated in the coil is Show Answer

Q407) The core of any transformer is laminated so as to Show Answer

Q408) In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4 A, then that in the secondary is Show Answer

Q409) A common transistor radio set requires 12 V (D.C.) for its operation. The D.C. source is constructed by using a transformer and a rectifier circuit, which are operated at 220 V(A.C.) on standard domestic A.C. supply. The number of turns of secondary coil are 24, then the number of turns of primary are ...... Show Answer