Practice Test


1) 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


2) 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


3) 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


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


5) Induction furnace is based on the heating effect of


6) Lenz's law is consequence of the law of conservation of


7) 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


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


9) 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


10) Which of the following statements is correct ?


11) 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


12) 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 ?


13) 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 ?


14) 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


15) 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


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


17) 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


18) Which of the statements, about a solenoid, is correct ?


19) 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


20) 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


21) 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


22) 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


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


24) 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.


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


26) The quality factor of an LCR circuit is equal to


27) 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


28) In a LCR series circuit, at resonant frequency


29) A choke is a :


30) 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


31) 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


32) 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


33) Alternating current can not be measured by DC ammeter because


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


35) The average value of alternating current over one complete cycle is


36) 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


37) 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


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


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


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


41) A device which converts electrical energy into mechanical energy is


42) Energy is stored in the choke coil in the form of


43) 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


44) 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


45) The power factor in an AC series L-R circuit is


46) 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


47) 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


48) 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


49) 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


50) 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


51) 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


52) 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


53) 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


54) 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


55) Lenz's law is a consequence of the law of conservation of :


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


57) 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 ?


58) 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 :


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


60) In a step-up transformer :


61) In a step-down transformer :


62) A small transformer does not :


63) A transformer has no :


64) Maximum efficiency of a transformer depends :


65) Auto transformer :


66) Transmission of electricity is done :


67) Induction furnaces work on the principle of :


68) Induction motor for A.C. devices works on the principal of :


69) Eddy currents do not cause :


70) The role of self-inductance in a circuit is equivalent to :


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


72) 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 :


73) 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 ):


74) In case of ideal step-down transformer :


75) 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 :


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


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


78) Armature current in D.C. motor is maximum when the motor has :


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


80) 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 :


81) In the electromagnetic induction, the induced e.m.f. in independent of


82) Self inductance of a straight conductor is :


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


84) The inductor may store energy :


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


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


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


88) 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 :


89) 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 :


90) A transformer changes :


91) 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 :


92) 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


93) 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.


94) 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


95) A conductor having no ohmic resistance resists the flow of changing current because


96) 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


97) 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


98) The induced charge in an inductance is independent of :


99) 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 :


100) 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


101) Quantity that remains unchanged in a transformer is


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


103) The unit of inductance is equivalent to


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


105) 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


106) 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


107) A.C. which we use in houses has peak value of nearly :


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


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


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


111) 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 :


112) 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.


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


114) At resonance the power factor of L-C-R circuit is :


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


116) 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 :


117) Ohm's law expressed as E= IR


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


119) 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 :


120) 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 :


121) 220 V a.c. is more dangerous than 220 V d.c. because :


122) L and R denote inductance and resistance. The dimensions of L/R is :


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


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


125) 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.


126) A choke coil may be used as a resistance in :


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


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


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


130) 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 :


131) An altering current in series LCR circuits is maximum if:


132) 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 :


133) The value of form factor for altering current is :


134) With fluorescent tube in A.C. circuit, we connect:


135) 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 :


136) A real capacitor can be represented in terms of ideal components as:


137) A real inductor can be represented as :


138) 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 :


139) 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 :


140) 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 :


141) The coil of a choke in a circuit :


142) 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 :


143) 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 :


144) 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 :


145) 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 :


146) 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 :


147) The coefficient of self inductance of a coil is given by :


148) 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 :


149) Which of the following is correct ?


150) 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 :


151) 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 :


152) Electric fan works on the principle of :


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


154) 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 :


155) In a LCR series circuit, at resonant frequency :


156) Eddy currents are produced in :


157) Which law follows the law of conservation of energy ?


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


159) 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:


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


161) 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 ?


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


163) 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 :


164) 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 :


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


166) One henry is equal to


167) 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 :


168) 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 :


169) 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 :


170) The core of a transformer is laminated because:


171) 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 :


172) 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 :


173) 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 ?


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


175) 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 :


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


177) 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


178) 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


179) 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


180) 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 :


181) The dimensions of the quantity L/CVR are equivalent to those of :


182) 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 :


183) 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


184) 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


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


186) 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 :


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


188) The constant speed of the frame is


189) The emf induced in the loop is


190) The potential difference between the points a and b is equal to


191) Which of the following represents the current generated by the apparatus


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


193) What will be the direction of current in the apparatus shown ?


194) 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.


195) The voltage drop across the resistor is given as


196) The resistance of the coil is


197) The voltage drop across the coil is


198) The device X can be


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


200) The device Y cannot be


201) Induced emf in the coil depends upon


202) Induced emf in the coil depends upon


203) 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


204) 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


205) 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


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


207) When power is drawn from the secondary coil of the transformer, the dynamic resistance


208) 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


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


210) The particle accelerator that uses the phenomenon of electromagnetic induction is the


211) 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


212) 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


213) 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


214) 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


215) 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


216) 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


217) Which type of losses donot occur in the transformer?


218) 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


219) 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


220) 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


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


222) 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


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


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


225) According to phenomenon of mutual inductance


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


227) 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


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


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


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


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


232) 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


233) Armature current in dc motor will be maximum when


234) 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


235) In a dc motor, induced e.m.f. will be maximum


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


237) For a large industrial city with much load variations the DC generator should be


238) Lenz’s law is statement of


239) Faraday’s laws are consequence of conservation of


240) 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


241) The square root of the product of inductance and capacitance has the dimension of


242) 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


243) 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?


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


245) When a metallic plate swings between the poles of magnet


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


247) 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


248) The net magnetic flux through any closed surface, kept in a magnetic field is


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


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


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


252) A magnet is dropped down an infinitely long vertical copper tube


253) 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


254) 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


255) Fleming’s left and right hand rule are used in


256) What is increased in step-down transformer


257) 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?


258) 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


259) A transformer is employed to


260) 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


261) According to Lenz’s law of electromagnetic induction


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


263) Which of the following is constructed on the principle of electromagnetic induction


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


265) Energy associated with a moving charge is due to


266) The induction coil works on the principle of


267) Electric fields induced by changing magnetic fields are


268) 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


269) 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


270) 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?


271) 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


272) 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?


273) When the current through a solenoid increases at a constant rate, the induced current


274) 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


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


276) Self induction of a solenoid is


277) 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


278) 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


279) Lenz’s law of electromagnetic induction corresponds to the


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


281) 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


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


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


284) 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


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


286) 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


287) 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


288) 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?


289) 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


290) When the speed of a dc motor increases the armature current


291) 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


292) 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


293) For previous objective, which of the following graphs is correct


294) 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


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


296) 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


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


298) 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


299) 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.


300) 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


301) 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


302) 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


303) Which of the following quantities remains constant in a step-down transformer ?


304) 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?


305) The power factor of good choke coil is


306) In Colpitt oscillator the feedback network consists of


307) 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


308) 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


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


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


311) 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


312) 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


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


314) If the coils of a transformer are made up of thick wire, then


315) At high frequency, the capacitor offer


316) 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


317) 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


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


319) 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


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


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


322) 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


323) Eddy current are produced when


324) Alternating current cannot be measured by DC ammeter because


325) 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


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


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


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


329) In a current carrying long solenoid, the field produced does not depend upon


330) 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


331) 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


332) 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


333) 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


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


335) 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


336) 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


337) 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?


338) 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


339) When the rate of change of current is unity, induced emf is equal to


340) The induced emf of a generator when the flux of poles is doubled and speed is doubled


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


342) 220 V, 50 Hz AC is applied to a resistor. The instantaneous value of voltage is


343) Current in the LCR circuit becomes extremely large when


344) Which of the following statement is incorrect?


345) 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


346) 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?


347) Consider a short magnetic dipole of magnetic length 10 cm. Its geometric length is


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


349) The power loss in AC circuit will be minimum when


350) What is the average power dissipation in an ideal capacitor in AC circuit?


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


352) The maximum voltage in DC circuit is 282V. The effective voltage in AC circuit will be


353) 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


354) 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


355) 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


356) Q-factor can be increased by having a coil of


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


358) Average power generated in an inductor connected to an AC source is


359) 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


360) 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


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


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


363) 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.


364) 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


365) 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


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


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


368) 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


369) Mutual inductance of two coils can be increased by


370) 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


371) A choke is preferred to a resistance for limiting current in AC circuit because