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

Q8) 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

Q9) 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

Q10) 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

Q11) 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

Q12) 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

Q13) 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

Q14) 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

Q15) Which of the statements, about a solenoid, is correct ? Show Answer

Q16) 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

Q17) 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

Q18) 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

Q19) A light bulb is rated at 100 W for a 220 V supply. The peak voltage of the source is Show Answer

Q20) 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

Q21) The quality factor of an LCR circuit is equal to Show Answer

Q22) In a LCR series circuit, at resonant frequency Show Answer

Q23) A choke is a : Show Answer

Q24) 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

Q25) 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

Q26) 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

Q27) Alternating current can not be measured by DC ammeter because Show Answer

Q28) If L and R denote inductance and resistance respectively which of the following has the dimensions of frequency ? Show Answer

Q29) 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

Q30) A device which converts electrical energy into mechanical energy is Show Answer

Q31) Energy is stored in the choke coil in the form of Show Answer

Q32) 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

Q33) 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

Q34) The power factor in an AC series L-R circuit is Show Answer

Q35) 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

Q36) 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

Q37) 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

Q38) 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

Q39) 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

Q40) 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

Q41) 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

Q42) 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

Q43) "The induced e.m.f. is always in such a direction so as to oppose the change that causes it" is called : Show Answer

Q44) 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

Q45) 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

Q46) A magnet is taken towards a coil and is moved (i) quickly (ii) slowly, then the induced e.m.f. is : Show Answer

Q47) In a step-up transformer : Show Answer

Q48) A small transformer does not : Show Answer

Q49) A transformer has no : Show Answer

Q50) Auto transformer : Show Answer

Q51) Transmission of electricity is done : Show Answer

Q52) Induction motor for A.C. devices works on the principal of : Show Answer

Q53) 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

Q54) 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

Q55) In case of ideal step-down transformer : Show Answer

Q56) 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

Q57) The back e.m.f. in a D.C. motor is maximum when the : Show Answer

Q58) Armature current in D.C. motor is maximum when the motor has : Show Answer

Q59) 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

Q60) In the electromagnetic induction, the induced e.m.f. in independent of Show Answer

Q61) Self inductance of a straight conductor is : Show Answer

Q62) If no. of turns per unit length in a solenoid is tripled, the self inductance of solenoid will Show Answer

Q63) The inductor may store energy : Show Answer

Q64) If the angular speed of rotation of an armature of alternator is doubled then induced e.m.f. will be : Show Answer

Q65) A transformer changes : Show Answer

Q66) 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

Q67) 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

Q68) A conductor having no ohmic resistance resists the flow of changing current because Show Answer

Q69) 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

Q70) The induced charge in an inductance is independent of : Show Answer

Q71) 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

Q72) Quantity that remains unchanged in a transformer is Show Answer

Q73) The direction of induced current is such that it opposes the very cause that produces it. This is the law of Show Answer

Q74) The unit of inductance is equivalent to Show Answer

Q75) 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

Q76) 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

Q77) A.C. which we use in houses has peak value of nearly : Show Answer

Q78) When two mutually perpendicular alternating magnetic fields superimpose on each other, the resulting field is : Show Answer

Q79) In a D.C. motors, the current flowing through the armature is minimum when induced e.m.f. is : Show Answer

Q80) 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

Q81) In an A.C. circuit, at resonance the phase difference between current and voltage is : Show Answer

Q82) At resonance the power factor of L-C-R circuit is : Show Answer

Q83) The power factor in a circuit connected at a A.C. power supply has a value which is : Show Answer

Q84) 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

Q85) Ohm's law expressed as E= IR Show Answer

Q86) The speed of fan is reduced by putting a rheostat in series with the fan, we consume: Show Answer

Q87) 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

Q88) 220 V a.c. is more dangerous than 220 V d.c. because : Show Answer

Q89) L and R denote inductance and resistance. The dimensions of L/R is : Show Answer

Q90) The time taken for a current to attain the maximum value in d.c. circuit containing 'L' and R depends upon : Show Answer

Q91) 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

Q92) 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

Q93) A choke coil may be used as a resistance in : Show Answer

Q94) The current in the a.c. circuit measures 5 A. Its maximum instantaneous magnitude will be : Show Answer

Q95) The parallel L-C circuit acts as a simple harmonic oscillator due to exchange of : Show Answer

Q96) In series L-C-R circuit at resonance, the voltage across the inductance is : Show Answer

Q97) 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

Q98) An altering current in series LCR circuits is maximum if: Show Answer

Q99) 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

Q100) The value of form factor for altering current is : Show Answer

Q101) 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

Q102) 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

Q103) 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

Q104) 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

Q105) 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

Q106) 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

Q107) 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

Q108) 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

Q109) The coefficient of self inductance of a coil is given by : Show Answer

Q110) 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

Q111) Electric fan works on the principle of : Show Answer

Q112) A horizontal straight conductor when placed along south north direction falls under gravity there is : Show Answer

Q113) 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

Q114) In a LCR series circuit, at resonant frequency : Show Answer

Q115) Eddy currents are produced in : Show Answer

Q116) Which law follows the law of conservation of energy ? Show Answer

Q117) 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

Q118) The self inductance of a solenoid of length L, the area of cross section A and having N turns is : Show Answer

Q119) 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

Q120) A 100 mH coil carries a current of 10 A. The magnetic energy stored in the coil is Show Answer

Q121) 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

Q122) 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

Q123) What is the equivalent inductance of a system of two inductors L joined in parallel : Show Answer

Q124) One henry is equal to Show Answer

Q125) 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

Q126) The core of a transformer is laminated because: Show Answer

Q127) 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

Q128) 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

Q129) 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

Q130) 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

Q131) 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

Q132) With the increase in frequency of an a.c. supply, the impedance of an L-C-R series circuit Show Answer

Q133) 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

Q134) 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

Q135) 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

Q136) 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

Q137) The dimensions of the quantity L/CVR are equivalent to those of : Show Answer

Q138) 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

Q139) 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

Q140) 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

Q141) If the capacity of a condenser is 1 farad then its resistance in a D.C. circuit will be Show Answer

Q142) 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

Q143) 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

Q144) Statement 1 : A short cylindrical bar magnet is dropped down a vertical aluminium pipe of slightly larger diameter, and of length several meters. It takes several seconds to emerge at the bottom, whereas an unmagnetized iron takes a fraction of a second.
Statement 2 : Eddy currents are generated in aluminium pipe which dampen the motion of bar magnet
Show Answer

Q145) Statement 1 : Magnetic flux is a vector quantity.
Statement 2 : Value of magnetic flux can be positive, negative or zero Show Answer

Q146) 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

Q147) The voltage drop across the resistor is given as Show Answer

Q148) The resistance of the coil is Show Answer

Q149) The voltage drop across the coil is Show Answer

Q150) Statement 1 : A resistance is connected to an A.C. source. Now a capacitor is included in series. The average power absorbed by the resistance will remain same.
Statement 2 : Capacitor does not consume power.
Show Answer

Q151) The device X can be Show Answer

Q152) 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

Q153) The device Y cannot be Show Answer

Q154) A bar magnet is kept along the axis of a coil with its N- pole facing the coil. The magnet is then rotated along its own axis. The induced current in the coil will be Show Answer

Q155) What is the change in magnetic flux produced in a coil in 25 s, if the induced e.m.f. in the coil is 2 mV? Show Answer

Q156) A copper ring is cut in such away, that there is a small gap between the two ends and it does not form a closed loop. This ring is kept horizontally and a bar magnet is dropped vertically through the ring, in such a way that its length is along the axis of the ring. The magnet falls with an acceleration which Show Answer

Q157) A straight metallic wire of length 1 m, is moving normally across a field of 0.1 T with a speed of 10 m/s. What is the e.m.f. induced between the ends of the wire? Show Answer

Q158) The dimensional formula for magnetic flux is Show Answer

Q159) A coil having effective area A is held with its plane normal to a magnetic field of induction B. The magnetic induction is quickly reduced to 25% of its initial value in 1s. The e.m.f. induced across the coil will be Show Answer

Q160) A coil of metal wire is kept stationary in a non-uniform magnetic field Show Answer

Q161) A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, then the current in the coil Show Answer

Q162) 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

Q163) A rod of length l is rotated about its one end, perpendicular to a magnetic field of induction B. What is the e.m.f. induced in the rod? Show Answer

Q164) The total charge induced in conducting loop when it is moved in magnetic field depends upon Show Answer

Q165) A thin circular ring of area A is held perpendicular to a uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of the circuit is R. If the ring is suddenly squeezed to zero area, then the charge flowing through the galvanometer is Show Answer

Q166) The self inductance of a coil which produces 5 V when the current changes from 3 A to 2 A in one millisecond is Show Answer

Q167) A 100 mH coil carries a current of 1 A. The energy stored in the magnetic field is Show Answer

Q168) The coefficient of mutual inductance of two coils is 10 mH. If the current flowing in one coil is 4A then the ted induced e.m.f. in the second coil will be Show Answer

Q169) The current in a coil decreases from 5 A to 0 in 0.1 sec. If the average e.m.f. induced in the coil is 50 V, then the self inductance of the coil is Show Answer

Q170) If the current flowing through a coil is reduced by 50%, then the energy in the coill Show Answer

Q171) What is the minimum value of inductance that can be obtained by combining three inductances of 1 H, 2 H and 3 H? Show Answer

Q172) The current in a coil changes from 0 to 2 A in 0.05 sec. If the induced e.m.f. is 80 V, the self inductance of the coil is: Show Answer

Q173) A coil has an inductance of 1 henry if a current changing at the rate of 3 A/S, induces Show Answer

Q174) The current passing through a choke coil of inductance 4 Henry is decreasing at the rate of 3 amp/sec. The e.m.f. developed across the coil is Show Answer

Q175) An e.m.f. of 40 mV is induced in a solenoid, when the current in it changes at the rate of 2 A/s. The self inductance of the solenoid is Show Answer

Q176) The self inductance of a coil having 100 turns is 10 mH. What is the magnetic flux linked with each turn of the coil, if a current of 4 mA is passed through the coil? Show Answer

Q177) A coil of self inductance 80 mH carries a current of 2 A. What is the energy stored in the coil? Show Answer

Q178) If a current of 3 A flowing in the primary coil is reduced to zero in 0.01 s, the e.m.f. induced in the secondary coil is 750 V. What is the mutual inductance between the two coils? Show Answer

Q179) An inductor stores the energy in Show Answer

Q180) Which one of the following is the unit of self inductance of a coil? Show Answer

Q181) The coefficient of mutual inductance of two coils is 6 mH. If the current flowing in one coil is 2 ampere, then the induced e.m.f. in the second coil will be Show Answer

Q182) The pointer of a dead-beat galvanometer gives a steady deflection because Show Answer

Q183) A 200 mH coil carries a current of 1 A. The energy stored in its magnetic field is Show Answer

Q184) In a coil, the current increases from 0 to 6A in 0.4 s. If an induced e.m.f. of 15 V is produced in the coil, then the coefficient of self-induction of the coil will be Show Answer

Q185) 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

Q186) The self inductance L of a solenoid of length l and area of cross-section A, with a fixed number of turns N increases as Show Answer

Q187) Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon Show Answer

Q188) If a current of 10 A flows in 1 s through a coil and the induced emf in the coil is 10 V, then, the self-inductance of the coil will be Show Answer

Q189) An emf of 100 mv is induced in a coil when the current in another nearby coil increases from 0 to 10 A in 0.1 second. What is the coefficient of mutual induction between the two coils? Show Answer

Q190) What is the dimensional formula for the coefficient of self induction? Show Answer

Q191) A current in a coil changes from +2A to -2A in 0.05 second. If the induced e.m.f. is 8V, then the self-inductance of the coil is Show Answer

Q192) If N is the number of turns in a circular coil, the value of its self-inductance varies as Show Answer

Q193) A circuit having a self inductance of 1 henry carries a current of 1 A. To prevent the sparking when the circuit is broken, a capacitor which can withstand 500 V is connected across the switch. What is the minimum value of the capacitance of the capacitor? Show Answer

Q194) The equivalent inductance of two inductances joined in parallel is 2.4 H and 10 H if they are joined in series. What is the difference between the inductances of the two combinations? Show Answer

Q195) The SI unit of inductance, henry, cannot be written as Show Answer

Q196) A coil is wound on a frame of rectangular cross-section. If all the linear dimensions of the frame are increased by a factor 2 and the number of turns per unit length of the coil remains the same, then the self-inductance of the coil will increase by a factor of Show Answer

Q197) A metal plate is getting heated. It can be because
Which is the wrong option from the above statements? Show Answer

Q198) In a step up transformer, the input voltage is 300 V and the output voltage is 15 KV. Then the ratio of the number of turns in the primary to that in the secondary is Show Answer

Q199) A step down transformer works on 220 volts a.c. mains. It is used to light a 100 W, 20 V bulb. The main current is 0.5 A. What is the efficiency of the transformer? Show Answer

Q200) A transformer has 100 turns in the primary and 500 turns in the secondary. If the primary is connected to 220 V DC supply, then the voltage developed across the secondary will be Show Answer

Q201) A step down transformer has a turn ratio of 5: 1. It is connected to 220 V, 50 Hz a.c. mains supply.
The Secondary voltage and the frequency of secondary voltage are given by Show Answer

Q202) A transformer has 230 volts applied to the primary and gives 4.6 V in the secondary. The secondary is connected to a load which draws a current of 5 A. The current in the primary is Show Answer

Q203) The primary winding of a transformer has 50 turns while its secondary has 500 turns. If the primary is connected to an a.c. supply of 220 V, 50 Hz, then the output at the secondary will be Show Answer

Q204) A Leclanche cell of e.m.f. 1.5 V is connected to the primary 50 of a step up transformer. If the turn ratio is 1:20, then the voltage developed across the secondary is Show Answer

Q205) A transformer is used to reduce the mains supply of 220V to 22V. If the currents in the primary and secondary are 2A and 15A respectively, then the efficiency of the transformer is Show Answer

Q206) The number of turns in the primary and secondary coils of a transformer are 200 and 800 respectively. If the voltage developed across the secondary is 240 V, then the potential difference across each turn of the primary will be Show Answer

Q207) In an ideal step down transformer, the input voltage is 400 V and the output voltage is 20 V. The output voltage is used to operate a device, having an impedance of 100 ohms. What is the current in the primary circuit? Show Answer

Q208) An ideal transformer has primary and secondary coils of 200 turns and 40 turns respectively. If the current in the primary coil is 3 A, then the value of current in the secondary coil will be Show Answer

Q209) The number of turns in the primary and secondary coils of a transformer are 100 and 300 respectively. If a 50 V, 50 Hz a.c. supply is applied to the primary coil of the transformer, then the P.D. per turn of the secondary will be Show Answer

Q210) A transformer having an efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are Show Answer

Q211) A step down transformer, transforms a supply line voltage of 2200 V into 220 V. The primary coil has 5000 turns. The efficiency and power transmitted by the transformer are 90% and 8 kW, respectively, then the power supplied is Show Answer

Q212) An a.c. source of 220 V is connected to the primary of a transformer. The output circuit draws a current of 2A at 440 V. If the efficiency of the transformer is 80%, then the current drawn by the primary windings of the transformer is Show Answer

Q213) In an ideal transformer, the number of turns in the primary is 120 and that in the secondary is 240. What is the secondary current if the primary current is 6 A? Show Answer

Q214) A transformer rated at 10 KW is used to connect a, 5 KV transmission line to a 250 V circuit. What is the ratio of the turns in the primary and secondary windings of the transformer? Show Answer

Q215) The output of a step-down transformer is measured to be 24 V when connected to a 12 W light bulb. What is the value of the peak current? Show Answer

Q216) A transformer with efficiency of 80% works at 4 kW and 100 V. The secondary voltage is 200 V. What are the values of primary and secondary currents? Show Answer

Q217) In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency w in a magnetic field B. The maximum value of e.m.f. generated in the coil is Show Answer

Q218) A transformer converts 240 V AC to 60 V AC. The secondary has 75 turns. The numbers of turns in the primary are Show Answer

Q219) Two coils P and Q are kept near each other. When no current flows through coil P and current increases in coil Q at the rate 10 A/s, the e.m.f. in coil P is 15 mV. When coil Q carries no current and current of 1.8 A flows through coil P, the magnetic flux linked with the coil Q is Show Answer