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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.
| 1. |
A parallel plate capacitor is connected to a battery as shown in figure. Consider two situations : . A : Key `K` is kept closed and plates of capacitors are moved apart using insulting handle. B : Key `K` is opened and plates of capacitors are moved apart using insulting handle. Choose the correct options (s).A. In `A : Q` remains same but `C` changesB. In `B : V` remains same but `C` changesC. In `A : V` remains same and hence `Q` changes.D. In `B : Q` remains same and hence `V` changes |
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Answer» Correct Answer - C::D Situation `A` : Since Key `K` is kept closed, so `V` remains same. As the plates of capacitors are moved apart, `C` changes and hence `Q` changes. Situation `B` : Since key `K` is opened, the charge on the plates `Q` remains same. But `C` changes as the plates are moved apart and hence `V` changes. |
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| 2. |
Find equivalent capacitance between points `A` and `B`. [Assume each conducting plate is having same dimensions and neglect the thickness of the plate `(epsilon_0A)/d=7muF` where A is area of plate]` `A. `2muF`B. `11muF`C. `12muF`D. `15 muF` |
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Answer» Correct Answer - B |
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| 3. |
In the given figure the capacitor of plate area `A` is charged upto charge `q`. The ratio of elongations (neglect force gravity) in springs `C` and `D` at equilibrium position is. .A. `(k_(1))/(k_(2))`B. `(k_(2))/(k_(1))`C. `k_(1)k_(2)`D. `sqrt((k_(1))/(k_(2))` |
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Answer» Correct Answer - B `F_(e)=k_(1)x_(1)=k_(2)x_(2) :. (x_(1))/(x_(2))=(k_(2))/(k_(1))`. |
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| 4. |
The ratio of charge to potential of a body is known asA. conductanceB. capacitanceC. inductanceD. reactance |
| Answer» Correct Answer - B | |
| 5. |
A parallel plate capacitor filled with a material of dielectric constant `K` is charged to a certain voltage and is isolated. The dielectric material is removed. Then (a) The capacitance decreases by a factor `K` (b) The electric field reduces by a factor `K` ( c) The voltage across the capacitor increases by a factor `K` (d) The charge stored in the capacitor increases by a factor `K`.A. `a` and `b` are trueB. `a` and `c` are trueC. `b` and `c` are trueD. `b` and `d` are true |
| Answer» Correct Answer - B | |
| 6. |
Force acting upon charged particle kept between the plates of a charged condenser is `F`. If one of the plates of the condenser is removed, force acting on the same particle will become.A. zeroB. `F//2`C. `F`D. `2 F` |
| Answer» Correct Answer - B | |
| 7. |
A condenser is charged and then battery is removed. A dielectric plate is put between the plates of condenser, then correct statement isA. `Q` constant `V` and `U` decreaseB. `Q` constant `V` increases `U` decreasesC. `Q` increases `V` decreases `U` increasesD. `Q,V` and `U` increase |
| Answer» Correct Answer - A | |
| 8. |
The gap between the plates of a parallel plate capacitor is filled with glass of dielectric constant `k=6` and of specific resistivity `100 G Omega m`. The capacitance of the capacitor is `4.0mF`. When a voltage of `2.0 kV` is applied to the capacitor, the leakage current of the capacitor will be.A. `2.0 xx 10^(-6) A`B. `3.0 xx 10^(-6) A`C. `1.5 xx 10^(-3) A`D. Zero |
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Answer» Correct Answer - C Let `Q_(0)` be the initial charge on the capacitor and `V_(0)` its initial potential. Let `A` be the area of the plates and `l` be the distance between them. Capacitance `C` of the capacitor is `C = (k epsilon_(0)A)/(l)` Resistance of the capacitor is `R=(rho l)/(A)=(rho k epsilon_(0))/(C)` ltbegt If `q` be the charge at time `t`, then the leakage current `i` is `i=(dq)/(dt)=(V)/(R)` where `V` is the volt age acros the capacitor at time `t`. But `q = CV` Hence `i=(dq)/(dt)=C(dV)/(dt)=(V)/(R)` Hence `(dV)/(V)=-(1)/(CR)dt`. The minus sign is because `dV` is negative. Integrating between limits, `V=V_(0)exp(-(t)/(CR))` Hence `i=(V)/(R)=(V_(0))/(R) exp(-(t)/(CR))` This gives the leakage current `i` at instant `t`. Initial leakage current is obtained at `t =0` Hence initial leakage current. `= (i)_(t=0)=(V_(0))/(R)=(Q_(0))/(CR)=(Q_(0))/(rho k epsilon_(0))` `= (4xx10^(-9)xx2xx10^(3))/(100 xx 10^(9)xx6xx8.85 xx10^(-12))=1.5 xx 10^(-6)A`. |
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| 9. |
Two metallic plates placed side by side form three capacitors. The infinity and first face of first plate is one capacitor, the second face of first plate and first face second plate forms second capacitor and the second face of second plate and infinity forms the third capacitor, but the capacitance of first and third capacitance are extremely small.A. Both A and R falseB. Both A and R true and R is not correct reason for AC. A is true and R is falseD. Both A and R are true and R is correct reason of A. |
| Answer» Correct Answer - A | |
| 10. |
An infinitely long solid cylinder of radius ` R` has a uniform volume charge density `rho`. It has a spherical cavity of radius `R//2` with its centre on the axis of cylinder, as shown in the figure. The magnitude of the electric field at the point `P`, which is at a distance `2 R` form the axis of the cylinder, is given by the expression `( 23 r R)/( 16 k e_0)` . The value of `k` is . . |
| Answer» Correct Answer - 6 | |
| 11. |
An infinity long uniform line charge distribution of charge per unit length `lambda` lies parallel to the y-axis in the `y-z` plane at `z=sqrt3/2` a(see figure). If the magnitude of the flux of the electric field through the rectangular surface ABCD lying in the `x-y` plane with its centre at the origin is `(lambdaL)/(nepsilon_0)` (`epsilon_0=` permittivity of free space), then the value of n is |
| Answer» Correct Answer - 6 | |
| 12. |
When air is replaced by a dielectric medium of constant `K`, the capacity of the condenser.A. increases `K` timesB. increases `K^(2)` timesC. remains unchargedD. decreases `K` times |
| Answer» Correct Answer - A | |
| 13. |
In order to increase the capacity of a parallel plate condenser one should introduce between the plates a sheet of (assume that the space is completely filled).A. MicaB. TinC. CopperD. Stainless steel |
| Answer» Correct Answer - A | |
| 14. |
A capacitor of `4 mu F` is connected as shown in the circuit. The internal resistance of the battery is `0.5 Omega`. The amount of charge on the capacitor plates will be . |
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Answer» Correct Answer - D No current flows in upper arm of the circuit. Current in lower arm of the circuit, `I=(E)/(R+r)=(2.5)/(2+0.5)=1A` `:.` Terminal potential difference of battery, `V = E - I_( r) = 2.5 -1 xx 0.5 = 2V` So charge on the capacitor plates, `Q = CV` `= 4 mu F xx 2V=8 mu C`. |
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| 15. |
Four identical capacitors are connected in series with a `10 V` battery as shown in the figure. The point `N` is earthed. The potentials of points `A` and `B` are `A. `10V,0V`B. `7.5V,-2.5V`C. `5V,-5V`D. `7.5V,2.5V` |
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Answer» Correct Answer - B |
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| 16. |
If the distance between the plates of parallel plate capacitor is halved and the dielectric constant of dielectric is doubled, then its capacity willA. deacrease teo timesB. increase two timesC. increase four timesD. remains the same |
| Answer» Correct Answer - C | |
| 17. |
An infinite number of identical capacitors each of capacitance `1 mF` are connected as shown in the figure. Then the equivalent capacitance between `A` and `B` is. .A. `1 mF`B. `2 mF`C. `1//2 mF`D. `0.75 mF` |
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Answer» Correct Answer - B `C_( R) = C+ ( C)/(2) + ( C)/(4) + ….` |
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| 18. |
The equivalent capacitance between terminals `A` and `B` in the circuit shown in figure is: A. `6C`B. `(2C)/5`C. `(2C)/3`D. `N``o``n``e` `of` `these` |
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Answer» Correct Answer - B |
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| 19. |
A network of six identical capacitors, each of capacitance C is formed as shown below. The equivalent capacitance between the point A and B is A. 3CB. 6CC. 3C/2D. 4C/3 |
| Answer» Correct Answer - D | |
| 20. |
The equivalent capacitance between the terminals X and Y in the figure shown will be- A. 100 pFB. 200 pFC. 300 pFD. 400 pF |
| Answer» Correct Answer - B | |
| 21. |
A parallel plate capacitor having plates of area S and plate separation d, has capacitance `C_1` in air. When two dielectrics of different relative primitivities (`epsilon_1=2` and `epsilon_2=4`) are introduced between the two plates as shown in the figure, the capacitance becomes `C_2`. The ratio `C_2/C_1` is A. `6//5`B. `5//3`C. `7//5`D. `7//3` |
| Answer» Correct Answer - D | |
| 22. |
The capacitance of a parallel plate capacitor with plate area `A` and separation `d` is `C`. The space between the plates in filled with two wedges of dielectric constants `K_(1)` and `K_(2)` respectively. Find the capacitance of resulting capacitor. |
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Answer» Correct Answer - `(CK_(1)K_(2))/(K_(2)-K_(1))ln`(K_(2))/(K_(1))`; where `C=(epsilon_(0)A)/(d)`. `(CK_(1)K_(2))/(K_(2)-K_(2))ln`(K_(2))/(K_(1)), where C=(epsilon_(0)A)/(d)`. |
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| 23. |
A condenser of capacity `10 mu F` is charged to a potential of `500 V`. Its terminals are then connected to those of an uncharged condenser of capacity `40 mu F`. The loss of energy in connecting them together is.A. 1 JB. `2.5 J`C. 10 JD. 12 J |
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Answer» Correct Answer - A `Delta E=(1)/(2)(C_(1)C_(2))/(C_(1)+C_(2))(V_(1)-V_(2))^(2)`. |
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| 24. |
The V versus x plot for six identical metal plates of cross-sectional area A is as shown. The equivalent capacitance between 2 and 5 is (Adjacent plates are placed at a separation d) : A. `(2 in_(0)A)/(d)`B. `(in_(0)A)/(d)`C. `(3 in_(0)A)/(d)`D. `(in_(0)A)/(2d)` |
| Answer» Correct Answer - B | |
| 25. |
The equivalent capacity between the points `X` and `Y` in the circuit with `C =1 mu F`. .A. `2 mu F`B. `3 mu F`C. `1 mu F`D. `0.5 mu F` |
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Answer» Correct Answer - A `C_(eff) =C_(1) + C_(2)`. |
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| 26. |
The plates of a parallel plate capacitor are pulled apart with a velocity `v`. If at any instant their mutual distance of separation is `x`, then magnitude of rate of change of capacitance with respect to time varies asA. `(1)/(d)`B. `(1)/(d^(2))`C. `d^(2)`D. d |
| Answer» Correct Answer - B | |
| 27. |
The plates of a parallel plate capacitor are pulled apart with a velocity `v`. If at any instant their mutual distance of separation is `x`, then magnitude of rate of change of capacitance with respect to time varies asA. `(1)/(x)`B. `(1)/(x^(2))`C. `x^(2)`D. `x` |
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Answer» Correct Answer - B `C=(Ain_(0))/(x)=Ain_(0)x^(-1)` `(dC)/(dt)=Ain_(0)(-1)x^(-2)(dx)/(dt)=-(Ain_(0))/(x^(2))v` `|(dC)/(dt)|prop(1)/(x^(2))` |
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| 28. |
A parallel plate air capacitor is connected to a battery. If plates of the capacitor are pulled farther apart, then which of the following statements is/are correct ?A. Strength of electric field inside the capacitor remains unchanged, if battery is disconnected before pulling the plateB. During the process, work is done by external force applied to pull the plates either battery is disconnected or it remains connectedC. Stored energy in the capacitor decreases if the battery remains connectedD. None of these |
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Answer» Correct Answer - A::B::C |
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| 29. |
given that potential differene across `1muF` capacitor is `10V`. Then, A. Potential difference acros `4muF` capacitor is `40V`B. Potential difference across `4muF` capacitor is `2.5V`C. Potential difference across `3muF` capacitor is `5V`D. Value of `E` is `70V` |
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Answer» Correct Answer - B |
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| 30. |
Five identical capacitor plates are arranged such that they make four capacitors each of `2muF.` The plates are connected to a source of emf `10 V`. The charge on plate `C` is A. `+20muC`B. `+40muC`C. `+60muC`D. `+80muC` |
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Answer» Correct Answer - B |
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| 31. |
LetC be the capacitance of a capacitor discharging through a resistor R. Suppose `t_1` is the time taken for the energy stored in the capacitor to reduce to half its initial value and `t_2` is the time taken for the charge to reduce to one-fourth its initial value. Then the ratio `t_1//t_2` will beA. 1B. `1//2`C. `1//4`D. 2 |
| Answer» Correct Answer - C | |
| 32. |
LetC be the capacitance of a capacitor discharging through a resistor R. Suppose `t_1` is the time taken for the energy stored in the capacitor to reduce to half its initial value and `t_2` is the time taken for the charge to reduce to one-fourth its initial value. Then the ratio `t_1//t_2` will beA. `1`B. `1//2`C. `1//4`D. `2` |
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Answer» Correct Answer - B `U_(0) = (q_(0)^(2))/(2C)U = (q_(0)^(2)e^(-2t_(1)//tau))/(2C) = (U_(0))/(2) = (q_(0)^(2))/(4C)` `e^(-2t_(1)//tau) = (1)/(2)` `t_(1) = (tau)/(2)ln2 ….(1)` and `q = q_(0)e^(-t_(2)//tau)` `(q_(0))/(4) = q_(0)e^(-t_(2)//tau),` `e^(-t_(2)//tau) = (1)/(4)` `t_(2) = 2tau In2 ...(2)` `(t_(1))/(t_(2)) =(1)/(4)` |
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| 33. |
There are `10` identical capacitors each of capacitance `C`.A. If all of them are connected in series, their equivalent capacitance is `C//10`B. If all of them are connected in parallel, their equivalent capacitance is `10 C`C. If two series combinations each having `5` capacitors are connected in parallel, their equivalent capacitance is `2C//5`D. If they are connected as five parallel combinations each one having two capacitors in series, their equivalent capacitance is `5C//2`. |
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Answer» Correct Answer - A::B::C::D Apply series and parallel combination of capacitors. |
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| 34. |
The plates of a parallel plate capacitor are charged by a battery and the battery is disconnected after the charging. Now, the plates are placed as shown in the figure. Then (plates are not parallel to each other). .A. the surface charge density is greater at point `A`B. the surface charge density is greater at point `B`C. the potential at points `A` and `B` is sameD. the potential at point `A` is greater |
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Answer» Correct Answer - A::C::D On a conductor potential is same as every point. |
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| 35. |
A capacitor is chared to store an energy `U`. The charging battery is disconnected. An edentical is now connected to the first capacitor in parallel. The energy in each capacitor is now.A. `(U)/(2)`B. UC. `(U)/(4)`D. `3U)/(2)` |
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Answer» Correct Answer - C `V=(C_(1)V_(1)+C_(2)V_(2))/(C_(1)+C_(2)),U=(1)/(2)(C_(1)+C_(2))V^(2)`. |
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| 36. |
Two, capacitors `A` and `B` are connected in series across a `100 V` supply and it is observed that the potential difference across them are `60 V` and `40 V`. A capacitor of `2 p.F` capacitance is now connected in parallel with `A` and the potential difference across B rises to `90 V`. Determine the capacitance of `A` and `B` |
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Answer» Correct Answer - `0.16muF, 0.24 muF` |
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| 37. |
An uncharged capacitor having capacitance `C` is connected across a battery of voltage `V`. Now the capacitor is disconnected and then reconnected across the same batterybut with reversed polarity. Then which of the statement is INCORRECTA. After reconnecting, heat energy produced in the circuit will be equal to two-third of the total energy supplied by batteryB. After reconnecting, no energy is supplied by batteryC. After reconnecting, whole of the energy supplied by the battery is converted into heatD. After reconnecting, thermal energy produced in the circuit will be equal to `2CV^(2)` |
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Answer» Correct Answer - B |
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| 38. |
The voltage applied across a capacitor having a capacitance of `10muF` is varies as shown in figure: At the time instant when the terminal voltage across capacitor is 600V calculate (a) The charge on capacitor ltBrgt (b) The energy stored in the capacitor (c) Draw the curve of current in connecting wires as a function of time. |
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Answer» Correct Answer - `6xx10^(-3)C;` (b) `1.8J;` |
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| 39. |
In the circuit shown in figure, each capacitor has a capacitance `C` and cell voltage is `E`. If switch `S` is closed, then calculate the work done by battery after closing the switch. |
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Answer» Correct Answer - `1/2CE^(2)` |
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| 40. |
In the circuit shown each capacitor has a capcitance `C`. The emf of the celll is `E`. If the switch `S` is closed then A. some positive charge will flow out of the positive terminal of the cellB. some positive charge will enter the positive terminal of the cellC. the amount of charge flowing through the cell will be CED. the amount of charge flowing through the cell will be `((4)/(3))`CE |
| Answer» Correct Answer - A::D | |
| 41. |
In the given network if potential difference between `p` and `q` is `2V` and `C_(2)=3C_(1)`, find the potential difference between `a` & `b`. |
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Answer» Correct Answer - `30V` |
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| 42. |
In the given network if potential difference between `p` and `q` is `2V` and `C_(2)=3C_(1)`, find the potential difference between `a` & `b`. |
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Answer» Correct Answer - `30V` |
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| 43. |
Two large parallel sheets charged uniformly with surfasce charge density `sigma` and `-sigma` are located as shown in the figure. Which one of the following graphs shows the variation of electric field along a line perpendicular to the sheets as one moves from `A` to `B` ? `A. B. C. D. |
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Answer» Correct Answer - B |
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| 44. |
A capacitor is charged by using a battery which is then disconnected. A dielectric slab is then slipped between the plates, which results inA. Reduction of charge on the plates and in crease of potential difference across the platesB. Increase in the potential difference across the plates, reduction in stored energy, but no change in the charge on the platesC. Decrease in the potential difference across the plates, reduction in stored energy, but no change in the charge on the platesD. None of the above |
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Answer» Correct Answer - C |
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| 45. |
While a capacitor remains connected to a battery and dielectric slab is applied between the plates, thenA. The charge supplied by the battery increases.B. The capacitance of the system increases.C. The electric field in the capacitor `B` increases.D. The electrostatic potential energy of `A` decreases. |
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Answer» Correct Answer - A::B |
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| 46. |
A parallel plate capacitor C with plates of unit area and separation d is filled with a liquid of dielectric constant `K=2`. The level of liquid is `d//3` initially. Suppose the liquid level decreases at a constant speed v, the time constant as a function of time t is- A. `(6 in_(0)R)/(5d+3vt)`B. `((15d+9vt)in_(0)R)/(2d^(2)-3dvi-9v^(2)t^(2))`C. `(6 in_(0)R)/(5d-3vt)`D. `((15d-9vt)epsilon_(0)R)/(2d^(2)+3dvt-9v^(2)t^(2))` |
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Answer» Correct Answer - A `tau=RC^(C=(epsilon_(0)A)/((d-x)+(x)/(k))k=2 x=(d)/(3)-vt)`. |
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| 47. |
A parallel plate capacitor C with plates of unit area and separation d is filled with a liquid of dielectric constant `K=2`. The level of liquid is `d//3` initially. Suppose the liquid level decreases at a constant speed v, the time constant as a function of time t is- A. `(6epsiolon_(0)R)/(5d+3Vt)`B. `((15d+9Vt)epsilon_(0)R)/(2d^(2)-3dVt-9V^(2)t^(3))`C. `(6epsilon_(0)R)/(5d-3Vt)`D. `((15d+9Vt)epsilon_(0)R)/(2d^(2)-3dVt-9V^(2)t^(3))` |
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Answer» Correct Answer - A Let the fall in the lavel in time `t` be `x`. Then `x=vt`. At that time the thickness of air in the capacitor is `d_(1) = ((2d)/(3)+vt)` and the thickness of liquid column is `d_(2) = ((d)/(3)-vt)`. At that time the equivalent capacitance is. `(1)/(C) =(1)/(C_(1)) +(1)/(C_(2)) =(((2d)/(3)+vt))/(in_(0)A) +(((d)/(3)-vt))/(Kin_(0)A)` put `A = 1` and `K = 2`, we get `C = (6in_(0))/(5d+3vt)` `tau = RC = (6in_(0)C )/(5d +3vt)` |
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| 48. |
Three long concentric conducting cylindrical shells have radii `R,2R` and `Rsqrt(2 )`. Inner and outer shells are connceted to each other. The capacitance across middle and inner shells per unit length is:A. `((1)/(3)in_(0))/(ln(2)`B. `(6pi in_(0))/(ln2)`C. `(pi in_(0))/(2ln2)`D. None |
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Answer» Correct Answer - B Capacitane per unit length of cylinderical capacitor `C = (2pi in_(0))/(lnR_(2)//R_(1))` It is a combination of two capacitor connected in parallel. `C_(eq) = C_(1) +C_(2) = (2pi in_(0))/(ln2) +(2pi in_(0))/(lnsqrt(2)) = (6pi in_(0))/(ln2)` |
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| 49. |
Figure shows three concentric conducting spherical shells with inner and outer shells earthed and the middle shell is given a charge `q`. Find the charge distribution of sphere |
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Answer» Correct Answer - `q_(1) =- (4q)/(25)` and `q_(2) = (21q)/(25)` Let potential of shells are `V_(1),V_(2)` and `V_(3)` and charge on them are `q_(1),q_(2),q_(3)` `V_(1) = (Kq_(1))/(r ) +(Kq)/(2.5r) +(Kq_(3))/(3.5r) = 0` `q_(1) +(2)/(5)q +(2)/(7) q_(3) = 0 …(1)` `V_(3) = (kq_(1))/(3.5r) +(kq)/(3.5r) +(kq_(3))/(3.5r) =0` `q_(1) +q +q_(3) = 0` from `(1)` and `(2)` `q_(1) =- (4)/(25)q`, and `q_(3) = (21q)/(25)` |
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| 50. |
Six point charges are kept at the vertices of a regular hexagon of side L and centre O, as shown in the figure. Given that `K=(1)/(4piepsilon_0)(q)/(L^2)`, which of the following statements(s) is (are) correct? A. The electric field at `O` is `6K` along `OD`B. The potential at `O` is zeroC. The potential at all points on the line `PR` is sameD. the point at all points on the line `ST` is same. |
| Answer» Correct Answer - A::B::C | |