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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
A time varying magnetic field is present in a cyclindrical region `R` as shown in the figure. A positive charge `q` is taken slowly from `P` to `Q` through `POQ`, the magnetic field varies with time as `B = B_(0) t` (where `B_(0)` is a constant) are directed into the plane of the paper. If `W` is the workdone then `W =` A. ZeroB. `B_(0)`C. InfiniteD. `2B_(0)` |
| Answer» In taking charge from `P` to `Q` one has to perform work against the force experinced by charge due to the induced electric field. The induced electric field is perpendicular to line `POQ` and hence `W_(1) = 0` | |
| 52. |
In the figure shown there exists a uniform time varying magnetic field `B = [(4 T//s) t + 0.3 T]` in a cylinderical region of radius `4m`. An equilateral traingualr conducting loop is placed in the magnetic field with its centroide on the axis of the field and its plane perpendicular to the field. A. `e.m.f.` induced in any one rod is `16 V`B. `e.m.f.` incduced in the complete `Delta ABC` is `48 sqrt(3) V`C. `e.m.f.` induced in the complete `Delta ABC` is `48V`D. `e.m.f.` induced in any one rod is `16 sqrt(3) V` |
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Answer» Correct Answer - B::D `e_(AB) = ((dB)/(dt))` area of `Delta AOB`, USING (E.M.I) `= (4)(1)/(2) xx (4 xx (sqrt(3))/(2) xx 2) xx 2` total emf of loop `= 3 xx (4 xx (1)/(2) xx 4 xx (sqrt(3))/(2) xx 2) xx 2` `= 2xx24sqrt(3) = 48sqrt(3) "Volt"` |
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| 53. |
A coil of inductance `8.4 mH` and resistance `6` `Omega` is connected to a `12 V` battery. The current in the coil is `1.0 A` at approximately the time.A. `500 s`B. `20 s`C. `35 s`D. `1 ms` |
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Answer» Correct Answer - D The current-time `(i-t)` equation in `L -R` circuit is given by [Growth of current in `L-R` circuit] `i = i_(0)(1-e^(-i//t_(L)))` -----(i) Where `i_(0) = (V)/(R ) = (12)/(6) = 2A` and `t_(L) = (L)/(R ) = (8.4 xx 10^(-3))/(6)` and `I = 1A , t = ?` Substituting these values in Eq. (i), we get `t = 0.97 xx 10^(-3) s` or `t = 0.97 ms t = 1m s` |
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| 54. |
A step down transformer has turn ration `100//1`. If secondary coil has `4amp` current then current in primary coil isA. `4 A`B. `0.04 A`C. `0.4 A`D. `400 A` |
| Answer» Correct Answer - B | |
| 55. |
The turn ratio of a transformers is given as `2:3`. If the current through the primary coil is `3 A`, thus calculate the current through load resistanceA. `1A`B. `4.5 A`C. `2 A`D. `1.5 A` |
| Answer» Correct Answer - C | |
| 56. |
In a step up transformer, if ratio of turns of primary to secondary is `1:10` and primary voltage si `230 V`. If the load current is `2A`. Then the current in primary isA. `20A`B. `10A`C. `2A`D. `1A` |
| Answer» Correct Answer - A | |
| 57. |
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 respectivelyA. `40 A, 16 A`B. `16 A, 40 A`C. `20 A, 40A`D. `40 A, 20 A` |
| Answer» Correct Answer - A | |
| 58. |
Two coils have a mutual inductance `0.005 H`. The current changes in the first coil according to equation `I=I_(0)sin omegat`, where `I_(0)=10A` and `omega=100pi`radian//sec`. The maximum value of e.m.f. in the second coil isA. `2pi`B. `5pi`C. `pi`D. `4pi` |
| Answer» Correct Answer - B | |
| 59. |
In the circuit shown in figure switch `S` is closed at time `t=0`. The charge which passes through the battery in one time constant is A. `(eR^(2)E)/(L)`B. `E = ((L)/(R ))`C. `(E L)/(eR^(2))`D. `(e L)/(E R)` |
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Answer» Correct Answer - C The current at time `t` is given by `i = i_(0) (1-e^(-t//tau))` Here `i_(0) = (E)/(R )` and `tau = (L)/(R )` `:. q = int_(0)^(tau)i d t = int_(0)^(t)i_(0)(1-e^(-t//tau))dt` `= (i_(0) tau)/(e) = (((E)/(R ))((L)/(R )))/(e) = (EL)/(eR^(2))` |
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| 60. |
A condenser in series with a resistor is connected through a switch to a battery of negligible internal resistance and having an emf of `12 V`. One second after closing the switch, the condenser is found to have a potential difference of `6V`. The time constant of the system isA. `2 s`B. `(1)/(log_(e) 2)`C. `log_(e)2`D. `log_(e) ((1)/(2))` |
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Answer» Correct Answer - B `q = q_(0)(1-e^(-t//Rc))`, `t = 1 "second"` `CV = CV_(0)(1-e^(-t//Rc)), (1)/(2) = e^(-t//Rc)` `ln 2 = (1)/(Rc)lne , RC = (1)/(ln 2)` |
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| 61. |
An inductance `L` and and a resistance `R` are connected in series to a battery of voltage `V` and negligible internal resistance through a switch. The switch is closed at `t = 0`. The charge that passes through the battery in one time constant is [`e` is base of natural logarithms]A. `(e R^(2)V)/(L)`B. `(VL)/(R )`C. `(VL)/(eR^(2))`D. `(eL)/(VR)` |
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Answer» Correct Answer - C `q = int i dt = int i_(0)(1-e^((-R )/(L)t))dt` |
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| 62. |
Two identical coaxial circular loops carry a current `i` each circulating int the same direction. If the loops approch each other the current inA. Current in each loop increasesB. Current in each loop remains the sameC. Current in each loop decreasesD. Current in one-loop increases and in the other it decreases |
| Answer» Correct Answer - C | |
| 63. |
Two circular coils `A` and `B` are facing each other as shown in figure. The current `i` through `A` can be altered A. There will be repulsion between A and B if i is increasedB. There will be attraction between A and B if i is increasedC. There will be neither attraction nor repulsion when `i` os chargedD. Attraction or repulsion between A and B depends on the direction of current. If does not depend whether the current is increased or decreased |
| Answer» Correct Answer - A | |
| 64. |
A coil of inductance `0.20 H` is connected in series with a switch and a cell of emf `1.6 V`. The total resistance of the circuit is `4.0 Omega`. What is the initial rate of growth of the current when the switch is closed?A. `0.050 As^(-1)`B. `0.40 As^(-1)`C. `0.13 As^(-1)`D. `8.0 As^(-1)` |
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Answer» Correct Answer - D `V = R I + L(dI)/(dt)`, at `t = 0, I = 0`, thus we have `(dI)/(dt) = (V)/(L) = (1.6)/(0.2) = 8A//s` |
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| 65. |
Two coils are at fixed location: When coil 1 has no corrent and the current in coil 2 increase at the rate of `15.0 A s^(-1)`, the emf in coil 1 is `25 mV`, when coil 2 has no current and coil 1 has a current of `3.6 A`, the flux linkange in coil 2 isA. `16 m Wb`B. `10 m Wb`C. `4.00 m Wb`D. `6.00 m Wb` |
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Answer» Correct Answer - D Coefficient of mutual inductance `M` is given by `|M| = (e_(1))/((di_(2)//dt)) = (phi_(2))/(i_(1))` `:. phi_(2) = (e_(1)i_(1))/((di_(2)//dt)) = ((25.0 xx 10^(-3))(3.6))/((15))` |
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| 66. |
A coil of wire having inductance and resistance has a conducting ring placed coaxially within it. The coil is connected to a battery at time t=0, so that a time-dependent current `1_(1)(t)` starts following through the coil. If `I_(2)(t)` is the current induced in the ring, and B (t) is the magnetic field at the axis of the coil due to `I_(1)(t)` then as a function of time `(tgt0)`, the product `I_(2)(t)B(t)`A. Increases with timeB. Decreases with timeC. Does not vary with timeD. Passes through a maximum |
| Answer» Correct Answer - D | |
| 67. |
Two circular coils have their centres at the same point. The mutual inductance between them will be maximum when their axesA. Are parallel to each otherB. Are at `60^(@)` to each otherC. Are at `45^(@)` to each otherD. Are perpendicular to each other |
| Answer» Correct Answer - A | |
| 68. |
Two circular coils can be arranged in any of the three situation shown in the figure. Their mutual inductance will be , , A. Maximum in situation (A)B. Maximum in situation (B)C. Maximum in situation (C)D. The same in all situations |
| Answer» Correct Answer - A | |
| 69. |
Two circular coils can be arranged in any of the three situation shown in the figure. Their mutual inductance will be , , A. maximum in situation (A)B. maximum in situation (B)C. maximum in situation (C)D. the same in all situations |
| Answer» Correct Answer - A | |
| 70. |
Two concentric and coplanar coils have radii a and `b ( gt gt a)` as shows in Fig. Resistance of the inner coil is `R`. Current in the outer coil is increased from `0` to `i`, then the total charge circulating the inner coil is A. `(mu_(0) i a^(2)pi)/(2RB)`B. `(mu_(0)i ab)/(2R)`C. `(mu_(0)i a b)/(2a)(pi b^(2))/(R )`D. `(mu_(0)ib)/(2pi R)` |
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Answer» Correct Answer - A `Delta q = (Delta phi)/(R ), phi = 0, phi_(f) = ((mu_(0))/(2)(i)/(b))(pi a^(2)) = (mu_(0)i a^(2) pi)/(2b)` `:. Delta phi = phi_(f) - phi_(i) = (mu_(0) i a^(2) pi)/(2b), " "` So, `Delta q = (mu_(0) i a^(2)pi)/(2 Rb)` |
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| 71. |
The inductance `L` of a solenoid of length `l`, whose windings are made of material of density `D` and resistivity `rho`, is (the winding resistance is`R`)A. `(mu_(0))/(4 pi l)(Rm)/(rho D)`B. `(mu_(0))/(4 pi l)(lm)/(rho D)`C. `(mu_(0))/(4 pi l)(R^(2)m)/(rho D)`D. `(mu_(0))/(2 pi R)(l m)/(rho D)` |
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Answer» Correct Answer - A For a sloenoid, `L = mu_(0) N^(2)(A)/(l)`. If `x` is the length of the wire and `a` is the area of cross-section, then `R = (rho x)/(a)` and `m = a xD` `Rm = (rho x)/(a) a x D, x = ((R m)/(rho D))` Also, `x = 2 pi rN, N = (X)/(2pi r) ( :. L = (mu_(0)N^(2)A)/(l))` `:. L = mu_(0)((x)/(2pir))^(2) (pi r^(2))/(l) = (mu_(0))/(4pi l)(Rm)/(rho D)` |
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| 72. |
Two identical circular loops of metal wire are lying on a table without touching each other. Loop-A carries a current which increases with time. In response, the loop-BA. remains stationaryB. is attracted by the loop `A`C. is repelled by the loop `A`D. rotates about its `CM`, with `CM` fixed |
| Answer» Correct Answer - C | |
| 73. |
A `100%` efficient transformer has `100` turns in the primary and `25` turns in its secondary coil. Of the current in the secondary coil is `4` amp, then the current in the primary coil isA. 1 ampB. 4 ampC. 8 ampD. 16 amp |
| Answer» Correct Answer - A | |
| 74. |
A transformer connected to `220` volt line shows an output of `2A` at `11000` volt. The efficiency is `100%`. The current drawn from from the line isA. `100 A`B. `200 A`C. `22 A`D. `11A` |
| Answer» Correct Answer - A | |
| 75. |
A solenoid of length 50 cm with 20 turns per cm and area of cross section 40 `cm^(2)` comletely surrounds another co-axial solenoid of the same length, area of cross seciton `25 cm^(2)` with 25 turns per cm. Calculate the mutual inductance of the system.A. `9.7 mH`B. `7.9 mH`C. `8.9 mH`D. `6.8 mH` |
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Answer» Correct Answer - B `M = (mu_(0)N_(1)N_(2)A_(2))/(l)` |
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| 76. |
Average energy stored in a pure inductance `L` when current `i` flows through it, isA. `Li^(2)`B. `2Li^(2)`C. `(Li^(2))/(4)`D. `(Li^(2))/(2)` |
| Answer» Correct Answer - D | |
| 77. |
A wire of length `2l` is bent at mid point so that the angle between two halves is `60^(@)`. If it moves as shown with a velocity `v` in a magnetic field `B` find the induced emf. |
| Answer» `e = Blv`. Here `l = "Effective length"= PQ` | |
| 78. |
A moving conductor coil in a magnetic field produces an induced e.m.f. This is in accordance withA. Amperes lawB. Coulomb lawC. Lenz’s lawD. Faraday’s law |
| Answer» Correct Answer - D | |
| 79. |
Calculate the mutual inducatnce between two coils when a current of `2A` changes to `6A` in `2` seconds and induces an emf of `20 mV` in the secondary coil |
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Answer» `|e| = M(dI)/(dt)` `20 xx 10^(-3) = M((6-2))/(2)` (or) `M = 10mH` |
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| 80. |
The number of turns in the primary coil of a transformer is `200` and the number of turns in the secondary coil is `10` if `240` volt `AC` is applied to the primary, the output from the secondary will beA. `48 V`B. `24 V`C. `12 V`D. `6 V` |
| Answer» Correct Answer - C | |
| 81. |
A magnet is brought towards a coil (i) speedily (ii) slowly then the induced e.m.f.//induced charge will be respectivelyA. Larger in case (i)B. Smaller in case (i)C. Equal in bothD. Larger or smaller depending upon the radius of the coil |
| Answer» Correct Answer - A | |
| 82. |
When ever the flux linked with a coil changes, thenA. current is always inducedB. an emf and a current are always inducedC. and emf is incduced but a current is never inducedD. an emf is always induced and a current is induced, when the coil is a closed one |
| Answer» Correct Answer - D | |
| 83. |
A circular loop of radius `R`, carrying current `I`, lies in `x-y` plane with its center at origin. The total magnetic flux through `x-y` plane isA. Directly proportional to IB. Directly proportional to RC. Directly proportional to `R^(2)`D. Zero |
| Answer» Correct Answer - D | |
| 84. |
A 50 turns circular coil has a radius of 3cm , it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B increased from 0.10 tesla to 0.35 tesla in 2 milliseconds . The average induced e.m.f. in the coil isA. `1.77 "volts"`B. `17.7 "volts"`C. `177 "volts"`D. `0.177 "volts"` |
| Answer» Correct Answer - B | |
| 85. |
A coil of area `100 cm^(2)` has `500` turns. Magnetic field of `0.1 "weber"//"metre"^(2)` is perpendicular to the coil. The field is reduced to zero in `0.1` second. The induced `e.m.f.` in the coil isA. 1 VB. 5 VC. 50 VD. Zero |
| Answer» Correct Answer - B | |
| 86. |
A two metre wire is moving with a velocity of 1 m/sec perpendicular to a magnetic field of `0.5 "weber"//m^(2)`. The e.m.f. induced in it will beA. `0.5` voltB. `0.1` voltC. 1 voltD. 2 volt |
| Answer» Correct Answer - C | |
| 87. |
Assertion (A): Whenever the magnetic flux linked with a closed coil changes there will be an induced emf as well as an induced current. Reason (R ) : Accroding to Faraday, the induced emf is inversely proportional to the rate of change of magnetic flux linked with a coil.A. Both `A` and `R` are true and `R` is the correct explanation of `A`B. Both `A` and `R` are true and `R` is not the correct explanation of `A`C. `A` is true but `R` is falseD. `A` is false but `R` is true. |
| Answer» Correct Answer - C | |
| 88. |
The graph Shows the variation in magnetic flux `phi(t)` with time through a coil. Which of the statements given below is not correct A. There is a change in the direction as well as magnitude of the induced emf between B and DB. The magnitude of the induced emf is maximum between B and CC. There is a change in the direction as well as magnitude of induced emf between A and CD. The induced emf is zero at B |
| Answer» Correct Answer - D | |
| 89. |
A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle `2 theta`. The earth’s magnetic field component in the direction perpendicular to swing is B . Maximum potential difference induced across the pendulum is A. `2BL sin ((theta)/(2)) (gL)^(1//2)`B. `BL sin ((theta)/(2)) (gL)`C. `BL sin ((theta)/(2)) (gL)^(3//2)`D. `BL sin ((theta)/(2)) (gL)^(2)` |
| Answer» Correct Answer - A | |
| 90. |
A straight wire of length `L` is bent into a semicircle. It is moved in a uniform magnetic field with speed `v` with diameter perpendicular to the field. The induced emf between the ends of the wire is A. `BLv`B. `2BLv`C. `2 pi BLv`D. `(2BvL)/pi` |
| Answer» Correct Answer - D | |
| 91. |
when the speed of a dc motor increase the armature currentA. IncreasesB. DecreasesC. Does not changeD. Increases and decreases continuously |
| Answer» Correct Answer - B | |
| 92. |
In an `LR` circuit, current at `t = 0` is `20 A`. After `2 s` it reduces to `18 A`. The time constant of the circuit is :A. `ln((10)/(9))`B. `2`C. `(2)/(ln(10/9))`D. `2 ln((10)/(9))` |
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Answer» `I = I_(0)e^(-t//tau) rArr 18 = 20 e^(-2//tau) rArr (10)/(9) = e^(2//tau)` `rArr ln (10)/(9) = (2)/(tau) rArr tau = (2)/(ln((10)/(9)))` |
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| 93. |
If in a coil rate of change of area is `(5meter^(2))/(milli second)`and current become `1 amp` from `2 amp` in `2xx10^(-3)` sec. if magnetic field is `1` Tesla then self-inductance of the coil isA. 2 HB. 5 HC. 20 HD. 10 H |
| Answer» Correct Answer - D | |
| 94. |
If in a coil rate of change of area is `(5meter^(2))/(milli second)`and current become `1 amp` from `2 amp` in `2xx10^(-3)` sec. if magnetic field is `1` Tesla then self-inductance of the coil isA. `2H`B. `5 H`C. `20 H`D. `10 H` |
| Answer» Correct Answer - D | |
| 95. |
A uniform magnetic field existsin region given by `vec(B) = 3 hat(i) + 4 hat(j)+5hat(k)`. A rod of length `5 m` is placed along `y`-axis is moved along `x`- axis with constant speed `1 m//sec`. Then the magnitude of induced `e.m.f` in the rod is :A. `0`B. `25 V`C. `20 V`D. `15 V` |
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Answer» Correct Answer - B `e = (vec(v) xx vec(B)). vec(l), e = [vec(i) xx (3 vec(i) + 4 vec(j) + 5 vec(k))].5 vec(j)` `rArr e = -25 V` |
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| 96. |
When the current through a solenoid increases at a constant rate, the induced currentA. Is constant and is in the direction of the inducing currentB. Is a constant and is opposite to the direction of the inducing currentC. Increases with time and is in the direction of the inducing currentD. Increases with time and opposite to the direction of the inducing current |
| Answer» Correct Answer - B | |
| 97. |
A conductor `AB` of length `l` moves in `x y` plane with velocity `vec(v) = v_(0)(hat(i)-hat(j))`. A magnetic field `vec(B) = B_(0) (hat(i) + hat(j))` exists in the region. The induced emf isA. zeroB. `2B_(0)lv_(0)`C. `B_(0)lv_(0)`D. `sqrt(2) B_(0)lv_(0)` |
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Answer» Correct Answer - A `vec(l), vec(v)` and `vec(B)` are coplanar. |
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| 98. |
Assertion : An induced emf is generated when magnet is withdrawn from the solenoid. Reason : The relative motion between magnet and solenoid induces emf.A. If both assertion and reason are t rue and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertionC. If assertion is true but reason is false.D. If the assertion and reason both are false |
| Answer» Correct Answer - A | |
| 99. |
An electric potential difference will be incduced between the ends of the conductor shown in the figure, if the conductor moves in the direction shown by A. `P`B. `R`C. `L`D. `M` |
| Answer» Correct Answer - D | |
| 100. |
When a rate of change of current in a circuit is unity, the induced emf is equal toA. Total flux linked with the coilB. induced chargeC. Number of turns in the circleD. Coefficient of self induction |
| Answer» Correct Answer - D | |