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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.
| 451. |
Along the axis of a dipole, direction of electric field is always in the direction of electric dipole moment p. Is this statement true of false? |
| Answer» False in the above figure we can see that directon of electric field is in the opposite direction of `p` between the two charges. | |
| 452. |
Three conducting spherical shells have charges `q,-2q` and `3q` as shown in figure. Find electric Potential at point P as shown in figure. |
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Answer» Correct Answer - A Potential P, `V_P=V_q-V_(-2q)+V_(3q)` =(kq)/r-(k(2q))/r+(k_(3q))/(3R)` Here `=kq(1/R-1/r)` here `k=1/(4piepsilon_0)` |
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| 453. |
Three charges `4q, Q` and `q` are in a straight line in the position of `0. l//2` and `l` respectively. The resultant force on `q` will be zero, if `Q=`A. Q = -qB. Q = qC. `Q = q^(2)`D. Q = 2q |
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Answer» Correct Answer - A The net force acting on charge q should be zero. `F=1/(4piin_(0))[(4qxxq)/l^(2)+(Qq)/((l//2)^(2))]=0` `therefore" "q+Q=0rArrQ=-q` |
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| 454. |
Two capacitor `C_(1)=2muF and C_(2)=6muF` are in series order connected is parallel to a third capacitor `C_(3)=4muF.` This combination is connected to 2 V battery. In charging these capacitor energy consumed by the battery is A. `2xx10^(-6)J`B. `11xx10^(6)J`C. `(32)/(3)xx10^(-6)J`D. `(16)/(3)xx10^(-6)J` |
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Answer» Correct Answer - B `"Total capacity, C"=(C_(1)C_(2))/(C_(1)+C_(2))+C_(3)=(2xx6)/(2+6)+4` `=(12)/(8)+4` `C=(44)/(8)4muF=(44)/(8)xx10^(-6)F` `because" Energy consumed by battery, U"=(1)/(2)CV^(2)` `rArr" "U=(1)/(2)xx(44)/(8)xx10^(-6)xx(2)^(2)=11xx10^(-6)J` |
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| 455. |
Figure shows the field lines on a positive charge. Is the work done by the field in moving a small positive charge from Q to P positive or negative? Give reason. |
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Answer» Negative; As the charge is displaced against the force exerted by the field. |
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| 456. |
Which of the following is not true for a region with a uniform electric field?A. It can have free charges.B. It may have uniformly distributed chargeC. It may contain dipolesD. none of the above |
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Answer» Correct Answer - D |
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| 457. |
A point charge `Q` is placed outside a hollow spherical conductor of radius `R` , at a distance `r (r gt R)` from its centre `C` . The field at `C` due to the inducted charges on the conductor isA. zeroB. `k(Q)/((r - R)^(2))`C. `k (Q)/(r^(2))` , directed towards `Q`D. `k(Q)/(r^(2))` , directed away from `Q` |
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Answer» Correct Answer - 3 The electric field at centre is zero . Due to `Q` , electric field will be `k(Q)/(r^(2))` away from `Q`, to balance this field , induced charge will produce electric field `k Q//r^(2)` towards `Q` , so that net electric field is zero. |
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| 458. |
A point charge `Q` is placed outside a hollow spherical conductor of radius `R` , at a distance `r (r gt R)` from its centre `C` . The field at `C` due to the inducted charges on the conductor isA. zeroB. `k Q/((r-R)^(2))`C. `k Q/(r^(2))`, directed towards `Q`D. `k Q/(r^(2))`, directed away from `Q` |
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Answer» Correct Answer - C |
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| 459. |
A spherical conductor `A` having charge `Q` lies inside a hollow spherical conductor `B`. (Choose incorrect option)A. Charge `-Q` will appear on the inner surface of `B`B. Charge `+Q` will appear on the outer surface of `B`C. If `B` is connected to earth , the charge `Q` on the outer surface flows to earthD. All options are correct |
| Answer» Correct Answer - 4 | |
| 460. |
A spherical shell of radius R has a charge +q units. The electric field due to the shell at a pointA. inside is zero and varies as `r^(-1)` outside itB. inside is constant and varies as `r^(-2)`C. inside is zero and varies as `r^(-2)` outside itD. inside is constant and varies as `r^(-1)` outside it |
| Answer» Correct Answer - C | |
| 461. |
A hollow metal ball carrying an electric charge produces no electric field at pointsA. interior pointB. outer pointC. beyond 2 mD. beyond 10 m |
| Answer» Correct Answer - A | |
| 462. |
Inside a hollow charged spherical conductor, the potentialA. is constantB. varies directly as the distance from the centreC. varies inversely as the distance from the centreD. varies inversely as the square of the distance from the centre |
| Answer» Correct Answer - B | |
| 463. |
Inside a hollow charged spherical conductor, the potentialA. increases with distanceB. is a constantC. decreases with distance from centreD. is zero |
| Answer» Correct Answer - B | |
| 464. |
Find potential difference `V_(AB)` between `A(0,0,0) and `B(1m,1m,1m)` in an electric field a. `E-yhati+xhatj` b. `E=3x^2yhati+x^3hatj` |
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Answer» Correct Answer - A::B::C a. `dV=-E.dr` `:. int_(B)^(A) dV=-int_(((1,1,1)))^(((0,0,0)))(yhati+xhatj).(dxhati+dyhatj+dzhatk)` or `V_A-V_B=-int_(((1,1,1)))^(((0,0,0))) (y dx+x dy)` or `V_(AB)=-int_(((1,1,1)))^(((0,0,0)))d(xy)` [as `y dx+x dy=d(xy)`] `:. V_(AB)=[xy]_(((1,1,1)))^(((0,0,0)))=1V` b. `dV=-E.dr` `:. int_B^A dV=-int_(((1,1,1)))^(((0,0,0)))(3x^2yhati+x^3hatj)*(dx^hati+dyhatj+dzhatk)` or `V_A-V_B=-int_(((1,1,1)))^(((0,0,0)))(3x^2ydx+x^3dy)` `=-int_(((1,1,1)))^(((0,0,0)))d(x^3y)` `:. V_(AB)=-[x^3y]_(((1,1,1)))^(((0,0,0)))=1V` |
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| 465. |
A thin metallic spherical shell contains a charge `Q` on it. A point charge `q` is placed at the centre of the shell and another charge `q_(1)` is placed outside it as shown in figure. All the three charges are positive The force on the charge at the centre isA. towards leftB. towards rightC. upwardD. zero |
| Answer» Correct Answer - 4 | |
| 466. |
Figure shows the electric field lines around an electric diple . Which of the arrows best represents the elctric field at point P ? ltbr gt ` .A. B. C. D. |
| Answer» Correct Answer - B | |
| 467. |
Calculate the area of paper required to construct a parallel plate capacitant of `0.004 muF`, if the dielectric constant of paper be `2.5` and its thickness `0.025 mm`. |
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Answer» Correct Answer - `4.52xx10^(3) m^(2)` `C = KC_(0) = K (in_(0) A)/(d)` |
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| 468. |
The plates of a parallel-plate capacitor in vacuum are `5.00 mm` apart and `2.00 m^2` in area. A potential difference of `10,000 V` is applied across the capacitor. Compute (a) the capacitance (b) the charge on each plate, and (c) the magnitude of the electric field in the space between them. |
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Answer» Correct Answer - `3.54xx10^(9) F ; 3.54xx10^(-6) C ; 2xx10^(5) NC^(-1)` Here, `d = 5xx10^(-3)m, A = 2 m^(2), V = 1000` volt, `C = (in_(0) A)/(d) = (8.85xx10^(-12)xx2)/(5xx10^(-3)) = 3.54xx10^(-9)F` `q = CV = 3.54xx10^(-9)xx1000 = 3.54xx10^(-6) C` `E = (sigma)/(in_(0)) = (Q)/(A in_(0)) = (CV)/(A in_(0)) = (CV)/(in_(0))` `= (3.54xx10^(-9)xx1000)/(2xx8.85xx10^(-12)) = 2xx10^(5) NC^(-1)` |
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| 469. |
A spark passes in air when the potential gradient at the surface of charged conductor is `4xx10^(6) Vm^(-1)`. What must be the radius of an insulated metal sphere which can be charged to a potential of `4xx10^(6) V` before sparking into air ? |
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Answer» Correct Answer - 1m As potential gradient `(dV)/(dr) = 4xx10^(6)V`, Therefore dr = 1m |
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| 470. |
A particle of mass m and charge q is released from rest in uniform electric field of intensity E. Calculate the kinetic energy it attains afect moving a distance x between the plates. |
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Answer» Correct Answer - qEx As `F = qE` `a = (F)/(m) = (qE)/(m)` As `v^(2) - u^(2) = 2` as, and `u = 0 :. V^(2) = 2as` `implies v^(2) = 2 ((qE)/(m))x xx = (2qEx)/(m)` `K.E. = (1)/(2) mv^(2) = (1)/(2) m ((2q Ex)/(m)) = qEx` |
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| 471. |
A charged ball of mass `8.4xx10^(16) kg` is found to remain suspended in a uniform electric field of `2xx10^(4) Vm^(-1)`. Calculate the charge on the ball. Given `g = 10 m//s^(2)` |
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Answer» Correct Answer - `4.2xx10^(-19) C` As `qE = mg :. q = (mg)/(E) = (8.4xx10^(-16)xx10)/(2xx10^(4))` `= 4.2xx10^(-19)C` |
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| 472. |
Calculate the energy per unit volume of a medium of dielectric constant 3, if the intensity of the electric field is `100V//m`.A. `1.328xx10^(-8) J//m^(3)`B. `4.2xx10^(-8) J//m^(3)`C. `13.28xx10^(-8) J//m^(3)`D. `42xx10^(-8) J//m^(3)` |
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Answer» Correct Answer - C `u=1/2in_(0)kE^(2)=(8.85xx10^(-12)xx3xx10^(4))/2` `=13.28xx10^(-8)J//m^(3)` |
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| 473. |
An insulated sphere of radius `R` has a uniform volume charge density `lambda`. The electric field at a point `A`, which is at distance `r` from its center is given by `(R gt r)`A. `(rho R)/(3 epsilon_(0))`B. `(rho r)/(epsilon_(0))`C. `(rho r)/(3 epsilon_(0))`D. `(3 rho r)/(epsilon_(0))` |
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Answer» Correct Answer - 3 `E = (1)/(4 pi in_(0)) (Qr)/(R^(3)) = (1)/( 4 pi in_(0)) . (rho . (4)/(3) pi R^(3) r)/(R^(3)) = (rho r)/(3 in_(0))` |
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| 474. |
What is the Van de Graaff generator? |
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Answer» The Van de Graaff generator is a high-voltage electrostatic generator that is used to produce very high potential differences of several million volts. It was constructed by US physicist Robert Van de Graaff in 1931. The high potential difference produced by the Van de Graaff generator is used to produce highenergy ion beams in a linear accelerator inside. |
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| 475. |
State the characteristics of electric lines of force. |
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Answer» 1. The lines of force originate from a positively charged object and end on a negatively charged object. 2. The lines of force neither intersect nor meet each other, as it will mean that electric field has two directions at a single point. 3. The lines of force leave or terminate on a conductor normally. 4. The lines of force do not pass through conductor i.e., electric field inside a conductor is always zero, but they pass through insulators. 5. Magnitude of the electric field intensity is proportional to the number of lines of force per unit area of the surface held perpendicular to the field. 6. Electric lines of force are crowded in a region where electric intensity is large. 7. Electric lines of force are widely separated from each other in a region where electric intensity is small. 8. The lines of force of an uniform electric field are parallel to each other and are equally spaced. |
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| 476. |
A charged cylinder of radius 2 cm has surface density of charge `8.85xx10^(-9)C//m^(2)`. It is placed in a medium of dielectric constant 5. The electric intensity at a point at a distance of 4 m from its axis isA. `5 V//m`B. `4 V//m`C. `3 V//m`D. `1 V//m` |
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Answer» Correct Answer - D `E=(sigmaR)/(in_(0)kr)=(8.85xx10^(-9)xx2xx10^(-2))/(8.85xx10^(-12)xx5xx4)=1V//m` |
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| 477. |
The surface charge density of a conducting sphere is `8.85xx10^(-10)C//m^(2)` and the electric field intensity at a distance of 4m from the centre of the sphere is `10^(-2)V//m`. The radius of the sphere, assuming the sphere to be in vacuum isA. 3 cmB. 4 mmC. 4 cmD. 4 km |
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Answer» Correct Answer - C `E=(sigmaR^(2))/(epsi_(0)kr^(2))` `therefore" "R^(2)=(Eepsi_(0)kr^(2))/sigma=(10^(-2)xx8.85xx10^(-12)xx1xx16)/(8.85xx10^(-10))` R = 4 cm |
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| 478. |
The electric field inside a parallel plate capacitor is E. Find the amount of work done in moving a charge q over a closed rectangular loop abcda. |
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Answer» Work done in moving a charge q from a to b = 0 Work done in moving a charge q from c to d = 0 This is because the electric field is perpendicular to the displacement. Now, work done from b to c = – work done from d to a Therefore, total work done in moving a charge q over a closed loop = 0. |
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| 479. |
The electric intensity at a point distant 1 m from the centre of a sphere of radius 25 cm in air is `10^(4)N//C`. The surface density of the charge on the surface of sphere isA. `1.416muC//m^(2)`B. `2.416muC//m^(2)`C. `1.446muC//m^(2)`D. `2muC//m^(2)` |
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Answer» Correct Answer - A `E=(sigmaR^(2))/(in_(0)kr^(2))` `therefore" "sigma=(10^(4)xx8.85xx10^(-12)xx1)/((25xx10^(-2))^(2))=1.416muC//m^(2)` |
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| 480. |
What is the magnitude of electric intensity due to a dipole of moment `2xx10^(-8)C-m` at a point distant `1 m` from the centre of dipole, when line joining the point to the center of dipole makes an angle of `60^(@)` with diople exis ? |
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Answer» Here, `p = 2xx10^(-8) C-m, r = 1 m`, `theta = 60^(@), E = ?` `E = (p)/(4pi in_(0) r^(3)) sqrt(3 cos^(2) theta+1)` `= (2xx10^(-8)xx9xx10^(9))/(1^(3)) sqrt(3 cos 60^(@) + 1)` `E = 238*1 N//C` |
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| 481. |
What will be the electrostatic potential energy of the dipole, when placed at right angle to the field ? |
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Answer» Zero. This is because, `U = -pE cos theta = -pE cos 90^(@) = Zero.` |
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| 482. |
How many electron- volt make one joule? |
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Answer» As `1 eV = 1.6xx10^(-19)` Joule = 1 eV `:.` 1 joule `= (1)/(1.6xx10^(-19)) eV = 0.625xx10^(19)` |
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| 483. |
Two charges `+20 muC and -20 muC` are held `1 cm` apart. Calculate the electric field at a point on the equatorial line at a distance of `50 cm` from the center of the dipole. |
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Answer» Here, ` q = +- mu C = +- 20xx10^(-6) C`, `2a = 1 cm = 10^(-2)m, r = 50 cm = (1)/(2) m` As `2 a lt lt r`, therefore, intensity on equatorial line of short dipole is ` E = (1)/(4pi in_(0)) (p)/(r^(3)) = (qxx2a)/(4pi in_(0) r^(3))` `= (9xx10^(9)xx20xx10^(-6)xx10^(-2))/((1//2)^(3))` `E = 1*44xx10^(4) N//C` |
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| 484. |
Positive and negative charges of `1 muC` each are placed at two points as shown in the figure. Find the potential difference between A and B |
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Answer» Correct Answer - 3000 V |
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| 485. |
What is the potential energy of two equal negative point charges `2 muC` each held 1m apart in air ? |
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Answer» `P.E. = (q_(1) q_(2))/(4pi in_(0) r) = (9xx10^(9) (-2xx10^(-6))^(2))/(1)` = 0.036 J |
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| 486. |
On moving a charge of ` 20 ` coulomb by ` 2 cm`, ` 2J` of work is done , the potential difference between the points is .A. 0.1 VB. 8VC. 2VD. 0.5V |
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Answer» Correct Answer - A By definition of electrostatic potential energy `DeltaU=q DeltaV` `DeltaV=(DeltaU)/q=2/20=0.1 V` |
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| 487. |
If a charge is moved against the Coulomb force of an electric field,(A) work is done by the electric field (B) energy is used from some outside source (C) the strength of the field is decreased (D) the energy of the system is decreased |
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Answer» (B) energy is used from some outside source |
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| 488. |
Two fixed charges `-2 Q ` and `Q` are locatted at the points with coordinates ( -3 a, 0) and (+3 a, 0) prespectively in the ` X- Y` plane . The expression for the potential ` V (x)` at a general point on the x-axis is given by .A. ` V(x) = 1/(4 pi varepsilon_0) [Q/(3a -x) - (2Q)/((3a+x))] for 0 lt xlt 3 a`B. ` V(x) = 1/(4 pi varepsilon_0) [2Q/(3a -x) - (2Q)/((3a+x))] for 0 lt xlt 3 a`C. ` V(x) = 1/(4 pi varepsilon_0) [Q/(3a -x) - (2Q)/((3a+x))] for 0 lt xlt 3 a`D. ` V(x) = 1/(4 pi varepsilon_0) [Q/(3a -x) - (2Q)/((3a+x))] for 0 lt xlt 3 a` |
| Answer» Correct Answer - A | |
| 489. |
A simple pendulum having caharge ` q_1` mass ma and effective length `1`, is suspended from a rigid support between the plates of charged horizontal capacitor. Electric field in the capacitor is perpendicular to the plates and directed vertically downwards . The time period of socillattion of the pendulum is given by :A. ` T= 2 pi sqrt ( l/(sqrt (g^2 + ((qE)/m)^2))`B. ` T= 2 pi sqrt ( l/(sqrt (g^2 + ((qE)/m)^2))`C. ` T= 2 pi sqrt ( l/(g^2 + (qE)/m)`D. ` T= 2 pi sqrt ( l/(g^2 + (qE)/m)` |
| Answer» Correct Answer - C | |
| 490. |
A simple pendulum having caharge ` q_1` mass ma and effective length `1`, is suspended from a rigid support between the plates of charged horizontal capacitor. Electric field in the capacitor is perpendicular to the plates and directed vertically downwards . the angle ` alpha` between the equilibrium position of the pendulum and the vertical is given by.A. ` alpha = sin^(-1) [ ((qQE//m)sin theta)/(h + (qE//m) vod theta) ]`B. ` alpha = cos ^(-1) [ ((qQE//m)sin theta)/(h + (qE//m) vod theta) ]`C. ` alpha = tan^(-1) [ ((qQE//m)sin theta)/(h + (qE//m) vod theta) ]`D. ` alpha = cos ^(-1) [ ((qQE//m)sin theta)/(h + (qE//m) vod theta) ]` |
| Answer» Correct Answer - D | |
| 491. |
A simple pendulum having caharge ` q_1` mass ma and effective length `1`, is suspended from a rigid support between the plates of charged horizontal capacitor. Electric field in the capacitor is perpendicular to the plates and directed vertically downwards . The time period of oscillation of the pendulum. if plates are held vertically , is given by :A. ` T= 2 pi sqrt ( l/(sqrt (g^2 + ((qE)/m)^2))`B. ` T= 2 pi sqrt ( l/(sqrt (g^2 + ((qE)/m)^2))`C. ` T= 2 pi sqrt ( l/(g^2 + (qE)/m)`D. |
| Answer» Correct Answer - A | |
| 492. |
A simple pendulum having caharge ` q_1` mass ma and effective length `1`, is suspended from a rigid support between the plates of charged horizontal capacitor. Electric field in the capacitor is perpendicular to the plates and directed vertically downwards . If the plates are oriented such thet plates made an angel ` theta` with the horizontal then the new time period of the oscillation of the pendulum is give by .A. ` T= 2 pi sqrt(l/sqrt (g^2 + ((qE)/m)^2 + 2g ((qQ)/m) sin theta)`B. ` T= 2 pi sqrt(l/sqrt (g^2 + ((qE)/m)^2 + 2g ((qQ)/m) sin theta)`C. ` T= 2 pi sqrt(l/sqrt (g^2 + ((qE)/m)^2 + 2g ((qQ)/m) sin theta)`D. |
| Answer» Correct Answer - B | |
| 493. |
A charged particle q is placed at the centre O of cube of length L(A B C D E F G H). Another same charge q is placed at a distance L from O. Then the electric flux through ABCD is A. (a) `q//4pi in_0L`B. (b) zeroC. (c) `q//2pi in_0L`D. (d) `q//3pi in_0L` |
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Answer» Correct Answer - B Both the charges are identical and placed symmetrically about ABCD. The flux crossing ABCD due to each charge is `1/6[q/in_0]` but in opposite directions. Therefore the resultant is zero. |
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| 494. |
If there are n capacitors in parallel connected to V volt source, then the energy stored is equal toA. (a) CVB. (b) `1/2nCV^2`C. (c) `CV^2`D. (d) `(1)/(2n)CV^2` |
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Answer» Correct Answer - B The equivalent capacitance of n identical capacitors of capacitance C is equal to nC. Eenrgy stored in this capacitor `E=1/2(nCV)V^2=1/2nCV^2` |
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| 495. |
Two identical charges are placed at the two corners of an equilateral triangle. The potential energy of the system is U. The work done in bringing an identical charge from infinity to the third vertex isA. `U`B. `2U`C. `3U`D. `4U` |
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Answer» Correct Answer - B U=1/(4piepsilon_0).q^2/a` (a=side of triangle) `W=U_f-U_i=3(1/(4piepsilon_0) q^2/a)-U` `=3U-U=2U` |
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| 496. |
Two identical particles, each having a charge of `2.0xx10^(-4) C` and then released. What would be the speeds of the particles when the separtion becomes large? |
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Answer» Correct Answer - `600 ms^(-1)` Here, `q = 2xx10^(-4)C, m = 10 g = 10^(-2) kg`, `r = 10 cm = 0.1m`. Let v , speed of each particle at infinite sepraration P.E. of two particles at the separationo of 10 cm. = K.E. of two particles at infinite separation `(1)/(4pi in_(0)) (q_(1) q_(2))/(r ) = (1)/(2) mv^(2) + (1)/(2) mv^(2)` `v^(2) = (1)/(4pi in_(0)) (q_(1) q_(2))/(r m) = (9xx10^(9)xx2xx10^(-4)xx2xx10^(-4))/(0.1xx10^(-2))` `= 36xx10^(4)` `v = 600 ms^(-1)` |
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| 497. |
A sphere is constructed around a positive point charge q. The work done in moving a unit positive charge on this sphere is numerically equal toA. infinityB. zeroC. capacity of sphereD. potential of sphere |
| Answer» Correct Answer - B | |
| 498. |
The dielectric constant of a metal isA. zeroB. oneC. kD. `infty` |
| Answer» Correct Answer - D | |
| 499. |
Two copper spheres A and B of same radii, one hollow and the other solid are charged to the same potential. Which of the two will hold more chargeA. AB. BC. solid sphere can not hold any chargeD. both the spheres will hold the same charge |
| Answer» Correct Answer - D | |
| 500. |
The capacitance of a capacitor does not depend uponA. either charge Q or potential VB. area of either platesC. distance between the platesD. nature of medium between the plates |
| Answer» Correct Answer - A | |