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InterviewSolution
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. |
Electric field at a point varies as `r^(0)` forA. An electric dipoleB. A point chargeC. A plane infinite sheet of chargeD. A line charge of infinite length |
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Answer» Correct Answer - c `E= sigma//(2 epsilon_(0))` |
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| 52. |
Two bodies `A` and `B` of definite shape are placed near one another. Electrostaitc attraction is found between the bodies, thenA. both bodies must be positive chargedB. both bodies must be negatively chargedC. both bodies must be oppositely chargedD. both `A` may be neutral |
| Answer» (d) Attraction may take place between like charge bodies, unlike charged bodis and charged body and neutral body. Hence (d) is correct. | |
| 53. |
If `sigma=` surface charge density `epsilon=` electric ermittivity the dimension of `(sigma)/(epsilon)` are same asA. electric forceB. electric field intensityC. pressureD. electric charge |
| Answer» Correct Answer - (b) | |
| 54. |
The ratio of electric fields on the axis and at equator of an electric dipole will beA. `1:1`B. `2:1`C. `4:1`D. None of these |
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Answer» Correct Answer - b `E_(a)=k(2p)/(r^(3))` and `E_(E)=(kp)/(r^(3))implies (E_(a))/(E_(E))= (2)/(1)` |
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| 55. |
Two positive ions , each carrying a charge `q` , are separated by a distance `d`.If `F` is the force of repulsion between the ions , the number of electrons missing from each ion will be (`e` being the charge on an electron)A. `(4piepsilon_(0)Fd^(2))/(e^(2))`B. `sqrt((4piepsilon_(0)Fe^(2))/(d^(2)))`C. `sqrt((4piepsilon_(0)Fd^(2))/(e^(2)))`D. `(4piepsilon_(0)Fd^(2))/(q^(2))` |
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Answer» Correct Answer - c Two positive ions each carrying a charge `q` are kept at a distance `d`, then it is found that force of repulsion between them is `F= (kqq)/(d^(2))= (1)/(4epsilon_(0)) (qq)/(d^(2))` where `q= n e :. F= (1)/(4epsilon_(0)) (n^(2)e^(2))/(d^(2))` `implies n= sqrt((4pi epsilon_(0)Fd^(2))/(e^(2)))` |
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| 56. |
A point charge `+Q` is positioned at the centre of a base of a square pyramid as shown. The flux through one of the four identical upper faces of the pyramid is A. `(Q)/(16 epsilon_(0))`B. `(Q)/(4 epsilon_(0))`C. `(Q)/(8 epsilon_(0))`D. None of these |
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Answer» Correct Answer - c Flux going in pyramid `=(Q)/(8epsilon_(0))` Which is divided equally among all `4` faces. `:.` Flux through one face `=(Q)/(8epsilon_(0))` |
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| 57. |
Assertion: Vehicle carrying highly inflammable materials have hanging chains, slightly touching the ground. Reason: The body of a vehicle gets charged when moving through air at high speed.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - a It is true that body of vehicle is charged, when the vehivle is moving through air at high speed Because of it, the vehicles, which are carrying highly inflammable material, have hanging chains, which touch slightly the ground. This chain trandfers the charge to the ground (earth). Hence there is no harm to the vehicle. |
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| 58. |
An electric dipole is placed in an electric field generated by a point chargeA. The net electric force on the dipole must be zeroB. The net electric force on the dipole may be zeroC. The torque on the dipole due to the field must be zeroD. The torque on the dipole due to the field may be zero |
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Answer» Correct Answer - d Point charge produces non-uniform electric field. |
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| 59. |
The electric field inside a conductorA. must be zeroB. may be nonzeroC. must be non zeroD. Both (a) and (c) are correct |
| Answer» Correct Answer - (b) | |
| 60. |
How many electrons should be removed from a coin of mass `1.6g`, so that it may float in an electric field of intensity of `10^(9)NC^(-1)` directed upward. (take `g= 10m//s^(2)`)A. `10^(6)`B. `10^(7)`C. `10^(9)`D. `10^(8)` |
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Answer» Correct Answer - d Let `n` be the number of electrons removed from the coin. Then, charge on coin, `q= +n e` Now, `qE= mg` Or `(n e)E=mg` or `n=(mg)/(eE)= (1.6xx10^(-3)xx10)/(1.6xx10^(-19)xx10^(9))= 10^(8)` |
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| 61. |
A dimensionless body having a phsical quantity varies as `1//r^(2)`, where `r` is distance from the body. This physical quantity may beA. gravitational potentialB. electric fieldC. gravitational fieldD. none of these |
| Answer» Correct Answer - (b),(c) | |
| 62. |
`+2C` and `+6C` two charges are repelling each other with a force of `12N`. If each charges is given `-2C` of charge is given `-2C` of charge, then the value of the force will beA. `4N` (Attractive)B. `4N` (Repulsive)C. `8N` (Repulsive)D. Zero |
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Answer» Correct Answer - d Resultant charges after adding the `-2C` be `(-2+2)=0` and `(-2+6) = +4C implies F=(kQ_(1)Q_(2))/(r^(2))= kxx(0xx4)/(r^(2))=0` |
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| 63. |
A particle of mass `m` and carrying charge `-q_(1)` is moving around a charge `+q_(2)` along a circular path of radius `r` period of revolution of the charge `-q_(1)` about `+q_(2)` isA. `4sqrt((pi^(3)epsilon_(0)mr^(3))/(q_(1)q_(2)))`B. `sqrt((pi^(3)epsilon_(0)mr^(3))/(q_(1)q_(2)))`C. `2sqrt((pi^(3)epsilon_(0)mr^(3))/(q_(1)q_(2)))`D. `3sqrt((pi^(3)epsilon_(0)mr^(3))/(q_(1)q_(2)))` |
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Answer» Correct Answer - a Suppose that the charge `-q_(1)` moves around the charge `q_(2)` along a circular path of radius `r` with spedd `v`. The necessary centripetal force is provided by the electronic force of attraction between the two charges i.e., `(1)/(4piepsilon_(0)).(q_(1)xxq_(2))/(r^(2))= (mv^(2))/(r)` Or `v= (1/(4piepsilon_(0)).(q_(1)xxq_(2))/(mr))^(1//2)` If `T` is period of revolution of the charge `-q_(1)` about `q_(2)` then `T=(2pir)/(v)` Subsituting for `v` we get `T = sqrt((16pi^(3)epsilon_(0)mr^(3))/(q_(1)q_(2)))` |
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| 64. |
Two charges `q_(1)` and `q_(2)` are kept on `x`-axis and electric field at different points an `x`-axis is plotted against `x`. Choose correct statement about nature and magnitudes of `q_(1)` and `q_(2)` A. `q_(1)+ve,q_(2)-ve, |q_(1)|gt|q_(2)|`B. `q_(1)+ve,q_(2)-ve, |q_(1)|lt|q_(2)|`C. `q_(1)-ve,q_(2)+ ve, |q_(1)|gt|q_(2)|`D. `q_(1)-ve,q_(2)+ve, |q_(1)|lt|q_(2)|` |
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Answer» Correct Answer - c From the directions of fields from graph, it is clear that `q_(1)` is negative and `q_(2)` is positive. Now since electric field is zero to the right of `q_(2)` hence `q_(2)` should be smaller in magnitude. |
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| 65. |
A square surface of side `L m` is in the plane of the paper. A uniform electric field `vec(E )(V//m)`, also in the plane of the paper, is limited only to the lower half of the square surface (see figure). The electric flux in `SI` units associated with the surface is: A. `EL^(2)//(2 epsilon_(0))`B. `EL^(2)//2`C. zeroD. `EL^(2)` |
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Answer» Correct Answer - c Electrtic flux `(phi_(e ))` is a measure of the number of field lines crossing a surface. The number of field lines passing through unit area `(N//A)` will be proportional to the electric field, or, `(N)/(A) prop Eimplies N prop EA` The quantity `EA` is the electric flux through surface `S`. In this problem, lines of force that enter the closed surface leave the surface, so no electric flux is bound to the system. Hence, electric flux is zero. |
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| 66. |
In relativistic mechanics `m=(m_(0))/(sqrt((1-(v^(2))/(c^(2))))` the equivalent relation in electricity for electric charge isA. `q=q_(0)`B. `q=(q_(0))/(sqrt((1-(v^(2))/(c^(2))))`C. `q_(0)=q/(sqrt((1-(v^(2))/(c^(2)))`D. `q=(q_(0)v)/c` |
| Answer» Correct Answer - (a) | |
| 67. |
The magnitude of electric field intensity E is such that, an electron placed in it would experience an electrical force equal to its weight is given byA. `m"ge"`B. `(mg)/e`C. `e/(mg)`D. `(e^(2))/(m^(2))g` |
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Answer» (b) Force on electron `|F|=qE=eE=mgimpliesE=(mg)/e` |
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| 68. |
Which one of the following is correct statement?A. Electric field is alwas conservativeB. Electric field due to varying magnetic field is conservativeC. Electric field is conservative due to electrostatic charges while non-conservative due to time varying magnetic fieldD. Electric field lines are alwas closed loops |
| Answer» (c) Electric field is conservative due to electrostatic charges, while non-conservative due to time varying magnetic field. | |
| 69. |
One brass plate is inserted between two charges. The force between two charges will beA. remain the sameB. increaseC. decreaseD. fluctuate |
| Answer» Correct Answer - (b) | |
| 70. |
A sure test of electification isA. attractionB. repulsionC. frictionD. induction |
| Answer» Correct Answer - (b) | |
| 71. |
If a body is charged by rubbing it. Its weightA. always decreases slightlyB. always increases slightlyC. may increase slightly or may decrease slightlyD. remains precisely the same |
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Answer» Correct Answer - C Weight may increase or decrease depending uopn whether the body is charged negatively or positively. |
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| 72. |
In a general, metallic ropes are suspended on the carries which take inflammable material. The reason isA. There speed is controlledB. To keep the center of gravity of the carrier nearer to the earthC. To keep the body of the carrier in contact with the earthD. Nothing should be placed under the carrier |
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Answer» Correct Answer - C For providing path to charge induced on the surface of the carries which take inflammable material |
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| 73. |
An oil drop of charge of 2 electrons fall freel with as terminal speed. Calculate the mas of oil drop so, it can move upward with same terminal speed, if electric field of `2xx10^(3) V//m` is applied.A. `3.0xx10^(-17)kg`B. `3.2xx10^(-17)kg`C. `2.5xx10^(-17)kg`D. `3.3xx10^(-17)kg` |
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Answer» (b) `mg=F=6pietarv` ………..(i) `qE-mg=6pi eta rv=F` …………..(ii) From eqs (i) and (ii) we get `qE=6 pi eta rv+mg=2mg` `E=(2mg)/q=(2mg)/(2e)=(mg)/e` `m=(2xx10^(3)xx1.6xx10^(-19))/10=3.2xx10^(-17)kg` |
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| 74. |
Assertion: Through large number of free electron are present in the metal, yet there is no current in the absent of electric field. Reason: In the absence of electric field, electrons move remdomly in all directionsA. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - b Free electrons present in the metal are moving randomly in all directions in of electric field. Hence, the average velocity of electrons is zero. Because of it the current does not flow in the metal in the absence of electric field. |
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| 75. |
Assertion: If the meduim between two charges is replaced by another medium of grater dielectric constant then the electric force between them decreases. Reason: Electric dipole moment varies inversely as the dielectric constant.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - c In a medium, `F_(m)= (F)/(K)` From above expression it is quite clear that greater the value of `K` smaller is the force between the two charges. Electric dipole moment is directly proportional to dielectric constant. |
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| 76. |
The spatial distribution of the electric field due to charges `(A,B)` is shown in figure. Which of the following statements is correct? A. `A` is `-ve` and `B+ve, |A|=|B|`B. Both are `+ve` but `AgtB`C. Both are `-ve` but `AgtB`D. `A` is `+ve` and `B-ve` and `|A|gt|B|` |
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Answer» Correct Answer - d Electric lines of force usually start (i.e., diverge out) from positive charge and end (i.e., converge) on negative charge or extends to infinity. Thus, A is p[ositive charge and B is negative charge. Also density of lines at A is more than that at B, i.e., `|A| gt |B|`. |
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| 77. |
Assertion. When charges are shared between any two bodies, no charge is really lost but some loss of energy does occur. Reason. Some energy disappears in the from of heat, sparking etc.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - b Charge is always conserved but energy is lost in the term of heat. |
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| 78. |
Two charges each equal to `eta q(eta^(-1) lt sqrt(3))` are placed at the corners of an equilateral triangle of side `a`. The electric field at the third corner is `E_(3)` where`(E_(0)= q//4piepsilon_(0)a^(2))`A. `E_(3)=E_(0)`B. `E_(3) lt E_(0)`C. `E_(3) gt E_(0)`D. `E_(3) ge E_(0)` |
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Answer» Correct Answer - c `E_(1)= (etaq)/(4piepsilon_(0)a^(2))`, `E_(2)=(eta q)/(4piepsilon_(0)a^(2))` Therefore `E = |vec(E_(1)) +vec(E_(2))|` `=sqrt(E_(1)^(2)+E_(2)^(2)+2E_(1)E_(2) cos 60^(@))=(sqrt(3)etaq)/(4piepsilon_(0)a^(2))`. Since `eta^(-1) lt sqrt(3),1 lt sqrt(3)eta, sqrt(3 eta) gt 1` `implies (sqrt(3)etaq)/(4piepsilon_(0)a^(2)) gt (q)/(4piepsilon_(0)a^(2))rArr E_(3) gt E_(0)(E_(0)= (q)/(4piepsilon_(0)a^(2)))`. |
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| 79. |
A point charge `+q` is placed at a distance `d` from an isolated conducting plane. The field at a point `P` on the other side of plane isA. directed perpendicular to the plane away from the planeB. directed perpendicular to the plane but towards the planeC. directed radially away from the point chargeD. directed radially towards the point charge |
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Answer» Correct Answer - a When a point positive charge brought near an isolated conducting plane. Some negative charge develops on the surface of the plane towards the charge and an equal positive charge develops on opposite side of the plane. This process is called charging by induction. |
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| 80. |
Assertion: The whole charge of a conductor cannot be transferred to another isolated conductor. ltbr Reason: The total transfer of charge from one to another is not possible.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - d The whole charge of conductor can be trandferred to another isolated conductor, if it is placed inside the hollow insulated conductor and connected with it. |
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| 81. |
Four charges are arranged at the corners of a square `ABCD`, as shown in the adjoining figure, The force on a positive charge kept at the centre `O` is A. zeroB. along the diagonal `AC`C. along the diagonal `BD`D. perpendicular to side `AB` |
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Answer» Correct Answer - c We put a unit positive charge at `O`. The resultant force due to the charge placed at `A` and `C` is zero and resultant force due to `B` and `D` is towards `D` along the diagonal `BD` |
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| 82. |
Assertion: The lightening conductor at the top of high building has sharp pointed ends. Reason: The surface density of charge at sharp points is very high resulting in setting up of electric wind.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - a A charged cloud induces opposite charge on pointed conductors. At sharp points of the conductor surface density of charge is very high and charge begins to leak from the pointed ends by setting up oppositely charged electric winds. This wind, when comes in the contact with the charge cloud, neutralizes some of its charge lowering the potential difference between the cloud and the building. Theis reduces the changes of lightening striking the building [if the lightning strikes the building, the charge is conducted to the earth and the building remains safe. |
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| 83. |
If the magnitude of intensity of electric field at a distance `x` on axial line and at a distance `y` on equatorial line on a given dipole are equal, then `x:y` isA. `1:1`B. `1:sqrt(2)`C. `1:2`D. `.^(3)sqrt(2):1` |
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Answer» Correct Answer - d `E_(ax ial)=E_(equat o rial)implies k.(2p)/(x^(3))=(k.p)/(y^(3))implies (x)/(y)= (2^(1//3))/(1)=^(3sqrt2:1)` |
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| 84. |
If `E_(a)` be the electric field strength of a short dipole at a point on its axial line and `E_(e)` that on the equatorial line at the same distance, thenA. `E_(e)=2E_(a)`B. `E_(a)= 2E_(e)`C. `E_(a)=E_(e )`D. None of the above |
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Answer» Correct Answer - b We have `E_(a)= (2kp)/(r^(3))` and `E_(e)= (kp)/(r^(3)), :. E_(a)= 2E_(e )` |
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| 85. |
What is the anle between the electric dipole moment and the elcetric field strength due to it on the equatorial lineA. `0^(@)`B. `90^(@)`C. `180^(@)`D. None of these |
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Answer» Correct Answer - c The direction of electric field intensity at a point on the equatrorial line of the dipole is opposite to the direction of dipole moment. |
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| 86. |
What is the magnitude of a point charge due to which the electric field `30cm` away the magnitude `2`? `[1//4 pi epsilon_(0)=9xx10^(9)Nm^(2)//C^(2)]`A. `2xx10^(-11)C`B. `3xx10^(-11)C`C. `5xx10^(-11)C`D. `9xx10^(-11)C` |
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Answer» (a) Electric field due to a point charge `E=q/(4piepsilon_(0)r^(2))` `:. q=Exx4piepsilon_(0)r^(2)=2xx1/(9xx10^(9))xx(30/100)^(2)` |
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| 87. |
Calculate the ratio of electrostatic to gravitational force between two electrons placed at certain distance in air. Given that `m_(e)= 9.1xx10^(-31) kg,e= 1.6xx10^(-19)C` and `G=6.6xx10^(-11)Nm^(-2)`.A. `8.4xx10^(42)`B. `3.2xx10^(41)`C. `4.2xx10^(42)`D. `1.2xx10^(42)` |
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Answer» Correct Answer - c `(F_("elec"))/(F_(graw))= 1/(4piepsilon_(0))*(exxe)/(r^(2))//G(m_(e)xxm_(e))/(r^(2))=1/(4piepsilon_(0))*(e_(2))/(Gm_(e)^(2))` Putting `G= 6.6xx10^(-11)Nm^(-2)`, `m_( e)= 9.1xx10^(-31) kg` and `e= 1.6xx10^(-19)C`, we get `(F_("elec"))/(F_(graw))= 4.2xx10^(42)`. |
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| 88. |
Three infinitely long charge sheets are placed as shown in figure. The electric field at point `P` is A. `(2 sigma)/(epsilon_(0))hat(k)`B. `-(2 sigma)/(epsilon_(0))hat(k)`C. `(4 sigma)/(epsilon_(0))hat(k)`D. `-(4sigma)/(epsilon_(0))hat(k)` |
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Answer» Correct Answer - b `vec(E )= (sigma)/(2epsilon_(0))hat(k)-(2 sigma)/(2epsilon_(0))hat(k)-(sigma)/(2epsilon_(0))k= -(2sigma)/(epsilon_(0))hat(k)` |
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| 89. |
A copper ball of density `8.6 gcm^(-3), 1 cm` is diameter is immersed in oil of density `0.8 dcm^(-3)`. If the ball remiand suspended in oil in a uniform electric field of intensity `36000NC^(-1)` acting in upward direction, what is the charge on the ball ?A. `1.1 muC`B. `4.2 muC`C. `2.4 muC`D. `3.7mu C` |
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Answer» Correct Answer - a Apparent weight of the ball `=mg-upthrust` `=4/3pir^(3)(rho-sigma)g=(4)/(3)pixx(0.5)^(3)xx(8.6-0.8)xx980` `= 4,002 dyn e= 4.0024xx10^(-2)N` Let `q` be the charge on the ball. As the ball remiand suspended, `qE=` apparent weightl of the ball or `q=("apparent weight")/(E)= (4.0024xx10^(-2))/(36,000)` `1.11xx10^(-6)C` |
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| 90. |
Assertion: A small metal ball is suspended in a uniform magnetic field with the help of an isulated thread. When a high energy `X` rays beam falls on the ball. Then the ball will be defected in the direction of electric field. Reason: The ball will oscillate in the field.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - c We know, that when high energy `X`-rays beam falls on metallic ball, then ball will emit the photoelectrons, so a ball will acquire positive charge because of it the ball will be deflected in the direction of electric field till equilibrium is reached. |
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| 91. |
Identical charges of magnitude `Q` are placed at `(n-1)` corners of a regular polygon of `n` sides each corner of the polygon is at a distance `r` from the centre. The field at the centre isA. `(kQ)/(r^(2))`B. `(n-1)(kQ)/(r^(2))`C. `n/((n-1)).(kQ)/(r^(2))`D. `((n-1))/n k Q/(r^(2))` |
| Answer» Correct Answer - (a) | |
| 92. |
A given charge is situated at a certain distance from an electric dipole in the end-on position experiences a force `F` If the distance of the charge is doubled, the force acting on the charge will beA. `2F`B. `F//2`C. `F//4`D. `F//8` |
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Answer» Correct Answer - d Force on charge `F=q(E_(a))=qxx(k.2p)/(r^(3))rArr F prop (1)/(r^(3))` When `r rarr` doubled,. `F rarr 1/8` times |
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| 93. |
An electric dipole is situated in an electric field of uniform intensity `E` whose dipole moment is `p` and moment of inertia is `I`. If the dipole is displaced slightly from the equilibrium position, then the angular frequency of its oscilliations isA. `((pE)/(I))^(1/2)`B. `((pE)/(I))^(3/2)`C. `((I)/(pE))^(1/2)`D. `((p)/(IE))^(1/2)` |
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Answer» Correct Answer - a When dipole is given a small angular displacement `theta` about its equilibrium position, the restoring torque will be `tau= -pE sin theta= -pE theta(as sin theta= theta)` or `I(d^(2)theta)/(dt^(2))= -pE theta(as tau= I alpha= 1 (d^(2)theta)/(dt^(2)))` or `(d^(2)theta)/(dt^(2))= -omega^(2) theta` with `omega^(2)= (pE)/(I)implies omega= sqrt((pE)/(I))` |
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| 94. |
Force of attraction between two point electric charges placed at a distance `d` in a medium is `F`. What distance apart should these be kept in the same medium, so that force between them becomes `F//3`?A. `2sqrt(3)d`B. `3d`C. `9d`D. `sqrt(3)d` |
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Answer» Correct Answer - d Let `q_(1)` and `q_(2)` be the two point charges. Then, force between the charges, when kept at a distance `d` apart, `F=(1)/(4piepsilon_(0))*(q_(1)q_(2))/(d^(2))` Suppose that force between the two charges becomes `F//3`, when the charges are kept at a distance `x` apart. Then `(1)/(4pi epsilon)*(q_(1)q_(2))/(x^(2))=F/3` or `1/(4piepsilon_(0))*(q_(1)q_(2))/(x^(2))=1/3(1/(4piepsilon_(0))*(q_(1)q_(2))/(d^(2)))` Or `x= sqrt(3)d` |
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| 95. |
Three charges each`+q`, are placed at the corners of an isosceles triangle `ABC` of sides `BC` and `AC, 2a, D` and `E` are the mid-points of `BC` and `CA`. The work done in taking a charge `Q` from `D` to `E` is A. `(eqQ)/(8piepsilon_(0)a)`B. `(qQ)/(4piepsilon_(0)a)`C. zeroD. `(3qQ)/(4piepsilon_(0)a)` |
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Answer» Correct Answer - c Here, `AC = BC` As `D` and `E` are the third mid points of `BC` and `CA`, the potential of these points should be equal. `V_(D)=V_(E )=V` The work done in talking a charge `Q` from `D` to `E` `W= Q[V_(E )-V_(D)]=Q[V-V]=0` |
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| 96. |
Infinite charges of magnitude `q` each are lying at `x= 1,2,4,8….meter` on `X`-axis. The value of intensity of electric field at point `x=0` due to these charges will beA. `12xx10^(9)qN//C`B. ZeroC. `6xx10^(9)qN//C`D. `4xx10^(9)qN//C` |
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Answer» Correct Answer - a Net field at origin `E= (q)/(4piepsilon_(0))[1/(1^(2))+1/(2^(2))+1/(4^(2)).....oo]` `(q)/(4piepsilon_(0))[1+1/4+1/(16)+....oo]` `=(q)/(4piepsilon_(0))[1/(1-1/4)]= 12xx10^(9)qN//C` |
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| 97. |
An infinite number of electric charges each equal to `5` nano-coulomb (magnitude) are placed along `X`-axis at `x=1 cm, x=2 cm,x=8cm`……and so on. In the setup if the consecutive charges have opposite sign, then the electrical field in Newton/Coulomb at `x=0` is `(1/(4piepsilon_(0))= 9xx10^(9)N-m^(2)//C^(2))`A. `12xx10^(4)`B. `24xx10^(4)`C. `36xx10^(4)`D. `48xx10^(4)` |
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Answer» Correct Answer - c `E= 1/(4piepsilon_(0)).[(5xx10^(-9))/((1xx10^(-2))^(2))-(5xx10^(-9))/((2xx10^(-2))^(2))+(5xx10^(-9))/((4xx10^(-2))^(2))-((5xx10^(_9)))/((8xx10^(-2))^(2))+ ....]` `implies E=(9xx10^(9)xx5xx10^(-9))/(10^(-4))[1-1/((2)^(2))+1/((4)^(2))-1/((8)^(2))+....]` `implies E= 45 xx 10^(4)[1+(1)/((4)^(2))+(1)/((16)^(2))+...] -45 xx 10^(4)[1/((2)^(2))+1/((8)^(2))+1/((32)^(2))+....]` `implies E= 45xx10^(4)[1/(1-1/(16))]-(45xx10^(4))/((2)^(2))[1+1/(4^(2))+1/((16)^(2))+....]` `E= 48xx10^(4)-12xx10^(4)= 36xx10^(4)N//C` |
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| 98. |
Two positively charged particles each having charge `Q` and are `d` distance apart. A third charge is introduced in midway on the line joining the two charges. Find the nature and magnitude of third charge so that the system is in equilibrium. A. `q=(Q)/4`B. `q=Q/4`C. `q=(3Q)/4`D. `q=-(3Q)/4` |
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Answer» (a) Condition for equilibrium `(kQ^(2))/(d^(2))+(kqQ)/((d//2)^(2))=0implies(kQ)/(d^(2))(Q+4q)=0` `q=(-Q)/4` |
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| 99. |
Assertion: A point charge is brought in an electric field. The field at a nearby point will increase, whatever be the nature of the charge. Reason: The electric field is independent of the nature of charge.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. if both Assertion and Reason are false |
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Answer» Correct Answer - d Electric field at the nearby point will be resultant of existing field and field due to the charge brought. It may increase or decrease if the charge is positive or negative depending on the position of the point with respect to the charge brought. |
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| 100. |
Assertion: A charged by cannot attract another uncharged body. Reason: Oppositely charged boils attract each other.A. if both Assertion and Reason are true and the Reason is correct explanation of the Assertion.B. If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.C. if Assertion is true, but the Reason is false.D. If Assertion is false but Reason is true. |
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Answer» Correct Answer - b A charged body and a uncharged body can attract each other. When such bodies are placed near each other, the induced charges of say `B` then induced charge on `B` may be less than charge on `A`. Hence,`ii-r` |
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