1638 + Interview Questions in ELECTROSTATICS IN GENERAL AWARENESS Page 23 InterviewSolution

1101.	Define polarization density.
Answer» The induced dipole moment developed per unit volme in a dielectric slab on placting it in as external electric field is called polarization density.

Discussion

1102.	The electric lines of force of two point charges are shown in fig. What is the value of the ratio `q_(1)//q_(2)` ?
Answer» Correct Answer - 3 From the knowledge of theory, `(q_(1))/(q_(2)) = (phi_(1))/(phi_(2)) = (3+3+6+6)/(3+3) = (18)/(6) = 3`

Discussion

1103.	What are the functions of a dielectric in a capacitor?
Answer» A dielectric material between the plates of a capacitor 1. increases the capacitance of the capacitor 2. provides mechanical support to the plates 3. increases the maximum operating voltage, i.e., the maximum voltage to which the capacitor may be charged without breakdown of the insulating property of the medium between the plates.

1103.

What are the functions of a dielectric in a capacitor?

Answer»

A dielectric material between the plates of a capacitor

1. increases the capacitance of the capacitor

2. provides mechanical support to the plates

3. increases the maximum operating voltage, i.e., the maximum voltage to which the capacitor may be charged without breakdown of the insulating property of the medium between the plates.

Discussion

1104.	What are dielectric substances ? Which of the following is a dielectric : Sillicon, mica,carbon ?
Answer» Dielectric substances are basically insulators, However, electric effects can be paased through them without actual conduction. Mica is a dielectric.

Discussion

1105.	If negative charge is enclosed by the surface, then the T. N. E. I. over the surface will beA. directed outwards and considered positiveB. directed inwards and considered positiveC. directed outwards and considered negativeD. directed inwards and considered negative
Answer» Correct Answer - D

Discussion

1106.	A Gaussian surface enclosed no charge. Which of the following is true for a point inside it ?A. electric field must be zeroB. electric potential must be zeroC. both electric potential and intensity must be zeroD. none of these
Answer» Correct Answer - A

Discussion

1107.	Express the unit of electric potential in terms of the basic units of S.I.
Answer» As electric potential `= ("work done")/("charge")` `= (ML^(2) t^(-2))/(AT) = ML^(2) T^(-3) A^(-1) = kg m^(2) s^(-3) A^(-1)`

Discussion

1108.	A wire AB of length L has linear charge density `lambda = Kx`, where x is measured from the end A of the wire. This wire is enclosed by a Gaussian hollow surface. Find the expression for electric flux through the surface`.
Answer» Here, `lambda = (dq)/(dx) = kx` , `sigma = ?` dq = Kx dx Total charge on the wire `q = int_(0)^(L) kx dx = [(Kx^(2))/(2)]_(0)^(L) = (KL^(2))/(2)` Electric flux through the Gaussion hollow surface is `sigma = (q)/(in_(0)) = (KL^(2))/(2in_(0))`

Discussion

1109.	Two square of sides a and 2a are placed in xy plane with their centers at the origin. Two charges, – q each, are fixed at the vertices of smaller square (lying on X axis). Two charges, Q each, are fixed at the vertices of bigger square on the X axis (see figure).(a) Find work required to slowly move the larger square to infinity from the position shown. (b) Find work done by the external agent in slowly rotating the inner square by `90^(@)` about the Y axis followed by a rotation of `90^(@)` about the Z axis.
Answer» Correct Answer - (a). `(8sqrt(2))/(3)(kqQ)/(a)` (b) `((8sqrt(2))/(3)-(4sqrt(2))/(sqrt(5)))(kqQ)/(a)`

Discussion

1110.	Electric field on the axis of a small electric dipole at a distance r is `vec(E)_(1)` and `vec(E)_(2)` at a distance of `2r` on a line of perpendicular bisector isA. `E_(2)=-E_(1)//8`B. `E_(1)=-E_(1)//16`C. `E_(2)=-E_(1)//4`D. `E_(2)=E_(1)//8`
Answer» Correct Answer - B

Discussion

1111.	Electric field on the axis of a small electric dipole at a distance r is `vec(E)_(1)` and `vec(E)_(2)` at a distance of `2r` on a line of perpendicular bisector isA. `(E_(0))/(16)`B. `(E_(0))/(16)`C. `(E_(0))/(8)`D. `- (E_(0))/(8)`
Answer» Correct Answer - D

Discussion

1112.	Figures shown electric field lines in which as electric dipole `vec(p)` is placed as shown .Which of the following statement is correct? A. The dipole will not not experience any forceB. The dipole will experience a force towards right.C. The dipole will experience a force towards left.D. The dipole will experience a force upwards
Answer» Correct Answer - C In Fig, spacing between electric lines of force increases from left to right . Therefore, `E` on left is greater that `E` on right. Force on `+q` charge of dipole is smaller and to the right. Force on `-q` charges of dipole is bigger and to the left. Hence, the dipole wil experience a net force towards the left.

Discussion

1113.	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 and 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
Answer» Correct Answer - A

Discussion

1114.	Electric charge is distributed uniformly on the surface of a spherical rubber ballon. Show how the value of electric intensity and potential vary (i) on the surface (ii), inside and (iii) outside ?
Answer» On the surface, E = constant, V = constant. Inside the surface , E = 0, V = constant = potential on the surface. Outside the ballon, `E prop (i)/(r^(2)) and V prop (1)/(r )` where r is distance of point from the center of the ballon.

Discussion

1115.	Fig. shows lines of constant potential in an electric field. Out of the three given points P,Q,R where is electric field intensity maximum and where is it minimum ?
Answer» Using the relation, `E = - (dV)/(dr)`, we find that electric intensity is maximum at P and minimum at R.

Discussion

1116.	Can we create an electric field in which all the lines of force are parallel but their density increases continusously in a direction per-pendicular to the lines of force, fig. ,
Answer» No, this is because work done in moving a unit positive charge along the closed path ABCD would no longer be zero, being more along AB, zero along BC and DA, Fig. this work done has to be zero, because electrostatic forces are conservative forces.

Discussion

1117.	The product of N.E.I. and given surface area of the closed surface is called asA. total normal electric inductionB. normal electric inductionC. electric potentialD. electric energy
Answer» Correct Answer - A

Discussion

1118.	The permittivity of medium is 26.55 × 10-12 C2/Nm2. The dielectric constant of the medium will be(A) 2 (B) 3 (C) 4 (D) 5
Answer» Correct option is: (B) 3

Discussion

1119.	Choose the correct optionA. A charged particle in an electric field always experiences a force either it is at rest or in motion and the direction of force is that of field if it is `+ve` ,and opposite to the field if `-ve`B. (i) For an external point (i.e., `r gt R`) , a solid or hollow , conducting or non-conducting charged sphere behaves as if whole of its charge is concentrated at its centre. (ii) In case of a hollow or solid conducting sphere for an internal point (i.e.,`r lt R`) , intensity `vec(E )` everywhere is dame and equal to zeroC. In case of spherical volume distribution of charge intensity an internal point `(r lt R)` will be due to the charge obtained in the sphere of radius `r`D. All options are correct
Answer» Correct Answer - 4

Discussion

1120.	`A` and `B` are two spherical conductors of the same extent and size. `A` is solid and `B` is hollow. Both are charged to the same potential . If the charges on `A` and `B` are `Q_(A)` and `Q_(B)` respectively, thenA. `Q_(A)` is less than `Q_(B)`B. `Q_(A)` is greater than `Q_(B)` but not doubleC. `Q_(A) = Q_(B)`D. `Q_(A) = 2Q_(B)`
Answer» Correct Answer - 3

Discussion

1121.	The product of electric intensity and permittivity constant of a dielectric medium is calledA. total normal electric inductionB. normal electric inductionC. electric potentialD. electric energy
Answer» Correct Answer - B

Discussion

1122.	The electric field intensity on the surface of a charged conductor isA. zeroB. directed normally to the surfaceC. directed tangentially to the surfaceD. directed along `45^(@)` to the surface
Answer» Correct Answer - 2

Discussion

1123.	The total number of tubes of force passing normally through the given area is called asA. normal electric inductionB. total normal electric inductionC. electric potentialD. electric power
Answer» Correct Answer - A

Discussion

1124.	The electric field intensity on the surface of a charged conductor isA. zeroB. maximumC. infinityD. `inE`
Answer» Correct Answer - A

Discussion

1125.	There is force of repulsion between two like charges, because electric lines of forceA. exert lateral pressure on one anotherB. exert normal pressure on one anotherC. exert no pressure on one anotherD. none of these
Answer» Correct Answer - A

Discussion

1126.	Like charges repel each other and unlike charges attract each other was proved byA. CoulombB. GilbertC. FaradayD. Franklin
Answer» Correct Answer - B

Discussion

1127.	What is the relevance of large value of `K (=81)` for water ?
Answer» It makes water a great solvent. This is because binding force of attraction between oppositely charged icons of the substance in water becomes `1//81`` of the force between these icons in air.

Discussion

1128.	There is force of attraction between two unlike charges because lines of force have tendencyA. to shrink along their length and they are under tensionB. to intersect each otherC. to elongate along their lengthD. none of these
Answer» Correct Answer - A

Discussion

1129.	What is the percentage change in distance if the force of attraction between two point charges increases to 4 times keeping magnitude of charges constant ?
Answer» Correct Answer - [Decreased to 50% of initial value]

Discussion

1130.	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`?
Answer» As `F prop 1//r^(2) :.` New distance `= sqrt(3) r`.

Discussion

1131.	An unchanged capacitor with a solid dielectric is connected to a similar air capacitor charged to a potential of `V_(0).`. If the common potential after sharing of charges becomes V, then the dielectric constant of the dielectric must beA. `V_(0)//V`B. `(V)/(V_(0))`C. `((V_(0)-V))/(V)`D. `((V_(0)-V))/(V_(0))`
Answer» Correct Answer - C `"Common potential, V"=("Total charge")/("Total capacitance")` `V=(C_(1)V_(1)+C_(2)V_(2))/(C_(1)+C_(2))=(0+CV_(0))/(KC+C)` `K=(V_(0))/(V)-1=(V_(0)-V)/(V)`

Discussion

1132.	An unchanged capacitor with a solid dielectric is connected to a similar air capacitor charged to a potential of `V_(0).`. If the common potential after sharing of charges becomes V, then the dielectric constant of the dielectric must beA. `(V_(0)-V)/V`B. `(V_(0)+V)/V`C. `V_(0)/V`D. `V_(0)/(2V)`
Answer» Correct Answer - A `V=(C_(1)V_(1)+C_(2)V_(2))/(C_(1)+C_(2))` `=(CKxx0+CV_(0))/(CK+C)=(CV_(0))/(C(K+1))=V_(0)/(K+1)` `K=(V_(0)-V)/V`

Discussion

1133.	A parallel plate condenser is made up of two plates, each of surface area `40cm^(2)`, separated by a distance of 0.4 cm. If a material of dielectric constant 10 is introduced between the plates, then the capacity of the condenser isA. 8.85 pFB. 88.5 pFC. 885 pFD. 585 pF
Answer» Correct Answer - B `A=40cm^(2),d=0.4cm,k=10,C=?` `C=(Akin_(0))/d=(40xx10^(-4)xx10xx8.85xx10^(-12))/(0.4xx10^(-2))` `=88.5xx10^(-12)F` = 88.5 pF

Discussion

1134.	The area of the plates of a parallel plate condenser is `A` and the distance between the plates is `10 mm`. There are two dielectric sheets in it, one of dieectirc constant `10` and thickness `6 mm` an dthe other of dielectric constant `5` and thickness `4 mm`. the capacity of the condenser isA. `5000/7in_(0)A`B. `500/7in_(0)A`C. `50/7in_(0)A`D. `50/14in_(0)A`
Answer» Correct Answer - A `C=(in_(0)A)/(t_(1)/K_(1)+t_(2)/K_(2))=(in_(0)A)/((6xx10^(-3))/10+(4xx10^(-3))/5)` `C=5000/7in_(0)A`

Discussion

1135.	Figure below show regular hexagons with charges at the vertices. In which of the following cases the electric field at the centre is not zero A. 1B. 2C. 3D. 4
Answer» Correct Answer - B

Discussion

1136.	Figure below show regular hexagons with charges at the vertices. In which of the following cases the electric field at the centre is not zero A. `1`B. `2`C. `3`D. `4`
Answer» Correct Answer - 6

Discussion

1137.	Find the capacitance of the infinite ladder between points X and Y, Fig.
Answer» Let C be the capacitance of the infinite ladder. As the ladder is infinite, addition of one more element of two capacitors `(1 muF and 2 muF)` across the points X and Y should not charge the total capacitance. Therefore, In fig, `2 muF` capacitance is in series with capacitance C. `:.` Their combined capacity `= (2 xx C)/(2 + C)` This combination is in parallel with `1 muF` capacitance. The equivalent capacity of the arrangement is `(1 + (2C)/(2 + C))` which must be equal to C i.e., `(1+n (2C)/(1 + C)) = C` or `C^(2) + 2C = 2 + 3C` or `C^(2) - C = 0 :. C = 2 or -1` Capacitance cannot be negative. `:. C = 2 muF`

Discussion

1138.	An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. It its dipole moment is along the direction of the field, the force on it and its potential energy are, respectively.(a) 2qE and minimum (b) qE and pE(c) zero and minimum (d) qE and maximum
Answer» (c) zero and minimum Potential energy, U = -pE cos θ For q = 0°; U = -pE, which is minimum

1138.

An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. It its dipole moment is along the direction of the field, the force on it and its potential energy are, respectively.(a) 2qE and minimum (b) qE and pE(c) zero and minimum (d) qE and maximum

Answer»

(c) zero and minimum

Potential energy, U = -pE cos θ

For q = 0°; U = -pE,

which is minimum

Discussion

1139.	Net charge within an imaginary cube drawn in a uniform electric field is always zero. Is this statement true or false?
Answer» Correct Answer - A Net charge from any closed surface in uniform electric field =0 `:.` Net charge inside any closed surface in uniform electric field `=0`

Discussion

1140.	A cube has sides of length `L = 0.2 `m. It is placed with one corner at the origin as shown in figure. The electric field is uniform and given by `E= (2.5 N//C) hati - (4.2 N//C) hatj`. Find the electric flux through the entire cube.
Answer» Given electric field is uniform electric field . Net flux from any closed surface in uniform electric field =0

Discussion

1141.	At distance of `5` cm and `10` cm outwards from the surface of a uniformly charged solid sphere, the potentials are `100 V` and `75 V` respectively. Then:A. Potential at its surface is 150 V.B. The charge on the sphere is `(5//3)xx10^(-9) C`.C. The electric field on the surface is 1500 V/m.D. The electric potential at its centre is 225 V.
Answer» Correct Answer - A::B::C::D

Discussion

1142.	Two equal balls having equal positive charge 'q' coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two ?
Answer» The force decreases.

Discussion

1143.	Force of attraction between two point charges `Q` and `-Q` separated by `d metre is F_(e )`. When these charges are placed on two identical spheres of radius `R = 0.3 d` whose centres are `d metre` apart , the force of attraction between them isA. greater than `F_(e )`B. equal to `F_(e )`C. less than `F_(e )`D. none of these
Answer» Correct Answer - 1 Now charges cannot be treated as point charges due to induction , charge is retributed , effective separation decreases , hence force increases.

Discussion

1144.	Two charge spheres separated at a distance d exert a force F on each other. If they are immersed in a liquid of dielectric constant K=2, then the force (if all conditions are same) isA. `(F)/(2)`B. `F`C. `2F`D. `4F`
Answer» Correct Answer - A

Discussion

1145.	A charge fo magnitude Q is divided into two parts q and `(Q - q)` such that the two parts exert maximum force on each other. Calculate the ratio `Q//q`.
Answer» Correct Answer - 2 Here, `F = (1)/(4pi in_(0)) (q(Q-q))/(r^(2))` As Q and r are fixed, so F is a function of q Force F will be maximum, only if `(dF)/(dq) = 0` or `(1)/(4pi in_(0)) (d)/(dq) [q (Q - q)] = 0` or `(d)/(dq) [q(Q - q)] = 0 or q(-1) + (Q - q) = 0` or `Q - 2q = 0 or Q = 2q` `(Q)/(q) = 2`

Discussion

1146.	How many mega coulombs of positive(or negative) Charge are present in `2.0 mol` of neutral hydrogen gas.
Answer» Correct Answer - 0.1927 MC Number of hydrogen molecules in 1.00 mole `= 6.023xx10^(23)`. Each molecule has two `"electrons"//"two protons"` `:. n = 2xx6.023xx10^(23)` `q =n e = 2xx0.623xx10^(23)xx1.6xx10^(-19)C` `19.27xx10^(4) C = 0.1927 MC`

Discussion

1147.	Which of the following represents the dimensions of FaradA. joule/voltB. volt/coulombC. coulomb/voltD. coulomb/joule
Answer» Correct Answer - C

Discussion

1148.	Unit of capacitance isA. henryB. ohmC. faradD. volt
Answer» Correct Answer - C

Discussion

1149.	What is the total charge on 75.0 kg of electrons ?
Answer» Correct Answer - `-1.33xx10^(13)C` Number of electrons (n) `= ("total mass")/("mass of each electron")` `= (75.0)/(9xx10^(-31)) = (25xx10^(31))/(3)` `q =n e = (25)/(3) xx 10^(31) xx (-1.6xx10^(-19))` `= -1.33xx10^(13)C`

Discussion

1150.	An arrangement which increases charge storing capacity without an appreciable increase in its potential isA. resistorB. conductorC. inductorD. capacitor
Answer» Correct Answer - D

Discussion

Explore topic-wise InterviewSolutions in .

Define polarization density.

The electric lines of force of two point charges are shown in fig. What is the value of the ratio `q_(1)//q_(2)` ?

What are the functions of a dielectric in a capacitor?

What are dielectric substances ? Which of the following is a dielectric : Sillicon, mica,carbon ?

If negative charge is enclosed by the surface, then the T. N. E. I. over the surface will beA. directed outwards and considered positiveB. directed inwards and considered positiveC. directed outwards and considered negativeD. directed inwards and considered negative

A Gaussian surface enclosed no charge. Which of the following is true for a point inside it ?A. electric field must be zeroB. electric potential must be zeroC. both electric potential and intensity must be zeroD. none of these

Express the unit of electric potential in terms of the basic units of S.I.

A wire AB of length L has linear charge density `lambda = Kx`, where x is measured from the end A of the wire. This wire is enclosed by a Gaussian hollow surface. Find the expression for electric flux through the surface`.

Electric field on the axis of a small electric dipole at a distance r is `vec(E)_(1)` and `vec(E)_(2)` at a distance of `2r` on a line of perpendicular bisector isA. `E_(2)=-E_(1)//8`B. `E_(1)=-E_(1)//16`C. `E_(2)=-E_(1)//4`D. `E_(2)=E_(1)//8`

Electric field on the axis of a small electric dipole at a distance r is `vec(E)_(1)` and `vec(E)_(2)` at a distance of `2r` on a line of perpendicular bisector isA. `(E_(0))/(16)`B. `(E_(0))/(16)`C. `(E_(0))/(8)`D. `- (E_(0))/(8)`

Electric charge is distributed uniformly on the surface of a spherical rubber ballon. Show how the value of electric intensity and potential vary (i) on the surface (ii), inside and (iii) outside ?

Fig. shows lines of constant potential in an electric field. Out of the three given points P,Q,R where is electric field intensity maximum and where is it minimum ?

Can we create an electric field in which all the lines of force are parallel but their density increases continusously in a direction per-pendicular to the lines of force, fig. ,

The product of N.E.I. and given surface area of the closed surface is called asA. total normal electric inductionB. normal electric inductionC. electric potentialD. electric energy

The permittivity of medium is 26.55 × 10-12 C2/Nm2. The dielectric constant of the medium will be(A) 2 (B) 3 (C) 4 (D) 5

The product of electric intensity and permittivity constant of a dielectric medium is calledA. total normal electric inductionB. normal electric inductionC. electric potentialD. electric energy

The electric field intensity on the surface of a charged conductor isA. zeroB. directed normally to the surfaceC. directed tangentially to the surfaceD. directed along `45^(@)` to the surface

The total number of tubes of force passing normally through the given area is called asA. normal electric inductionB. total normal electric inductionC. electric potentialD. electric power

The electric field intensity on the surface of a charged conductor isA. zeroB. maximumC. infinityD. `inE`

There is force of repulsion between two like charges, because electric lines of forceA. exert lateral pressure on one anotherB. exert normal pressure on one anotherC. exert no pressure on one anotherD. none of these

Like charges repel each other and unlike charges attract each other was proved byA. CoulombB. GilbertC. FaradayD. Franklin

What is the relevance of large value of `K (=81)` for water ?

There is force of attraction between two unlike charges because lines of force have tendencyA. to shrink along their length and they are under tensionB. to intersect each otherC. to elongate along their lengthD. none of these

What is the percentage change in distance if the force of attraction between two point charges increases to 4 times keeping magnitude of charges constant ?

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`?

An unchanged capacitor with a solid dielectric is connected to a similar air capacitor charged to a potential of `V_(0).`. If the common potential after sharing of charges becomes V, then the dielectric constant of the dielectric must beA. `(V_(0)-V)/V`B. `(V_(0)+V)/V`C. `V_(0)/V`D. `V_(0)/(2V)`

A parallel plate condenser is made up of two plates, each of surface area `40cm^(2)`, separated by a distance of 0.4 cm. If a material of dielectric constant 10 is introduced between the plates, then the capacity of the condenser isA. 8.85 pFB. 88.5 pFC. 885 pFD. 585 pF

Figure below show regular hexagons with charges at the vertices. In which of the following cases the electric field at the centre is not zero A. 1B. 2C. 3D. 4

Figure below show regular hexagons with charges at the vertices. In which of the following cases the electric field at the centre is not zero A. `1`B. `2`C. `3`D. `4`

Find the capacitance of the infinite ladder between points X and Y, Fig.

Net charge within an imaginary cube drawn in a uniform electric field is always zero. Is this statement true or false?

A cube has sides of length `L = 0.2 `m. It is placed with one corner at the origin as shown in figure. The electric field is uniform and given by `E= (2.5 N//C) hati - (4.2 N//C) hatj`. Find the electric flux through the entire cube.

Two equal balls having equal positive charge 'q' coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two ?

Two charge spheres separated at a distance d exert a force F on each other. If they are immersed in a liquid of dielectric constant K=2, then the force (if all conditions are same) isA. `(F)/(2)`B. `F`C. `2F`D. `4F`

A charge fo magnitude Q is divided into two parts q and `(Q - q)` such that the two parts exert maximum force on each other. Calculate the ratio `Q//q`.

How many mega coulombs of positive(or negative) Charge are present in `2.0 mol` of neutral hydrogen gas.

Which of the following represents the dimensions of FaradA. joule/voltB. volt/coulombC. coulomb/voltD. coulomb/joule

Unit of capacitance isA. henryB. ohmC. faradD. volt

What is the total charge on 75.0 kg of electrons ?

An arrangement which increases charge storing capacity without an appreciable increase in its potential isA. resistorB. conductorC. inductorD. capacitor