1638 + Interview Questions in ELECTROSTATICS IN GENERAL AWARENESS Page 17 InterviewSolution

801.	In S.I. system, coulomb-meter is unit ofA. electric intensityB. electric potentialC. electric fluxD. electric dipole moment
Answer» Correct Answer - D

Discussion

802.	In the following figure an isolated charged conductor is shown. The correct statement will be - A. `E_(A) gt E_(B) gt E_(C) gt E_(D)`B. `E_(A) lt E_(B) lt E_(C) lt E_(D)`C. `E_(A)=E_(B)=E_(C)=E_(D)`D. `E_(B)=E_(C)` and `E_(A) gt E_(D)`
Answer» Correct Answer - B Conductor is equipotential body, `V_(A)=V_(B)=V_(C)=V_(D)` For equipotential surface, charge is directly proportional to radius of curvature here `r_(D) gt r_(C) gt r_(B) gt r_(A)` and surface charge density is inversly proportional to radius of curvature. `sigma_(A) gt sigma_(B) gt sigma_(C) gt sigma_(D)` Electricfied is directly proportional to surface charge density `E_(A) gt E_(B) gt E_(C) gt E_(D)`

Discussion

803.	A family of equipotential surface are shown. The direction of the electric field at point A is along- A. ABB. ACC. ADD. AF
Answer» Correct Answer - D Electric field is always perpendicular to quipotential surface. Opposite to electric field potential increases.

Discussion

804.	A hollow conducting sphere is placed in an electric field produced by a point charge placed at `P` as shown in figure. Let `V_(A), V_(B), V_(C )` be the potentials at points `A, B and C` respectively. Then A. `V_(C) gt V_(B)`B. `V_(B) gt V_(C)`C. `V_(A) gt V_(B)`D. `V_(A)=V_(B)`
Answer» Correct Answer - D Conducting surface behave as equipotential surface.

Discussion

805.	Two point charges +9e and +e ,
Answer» Two point charges +9e and +e are kept at a distance

Discussion

806.	On our return from an excursion trip in our school, I noticed a bird sitting on a high voltage electric wire. I curiously noticed the bird and found to my surprise that the bird flew off after sometime without any electrical shock. This incident made me think of another incident that took place near my house last week where, a boy, who climbed to take a kite, got severe jolt of electric current. I immediately approached my school physics teacher for an explanation. My teacher explained the effect of electrical current which I told my mother that evening.(i) What are the values associated with the above incident ?(ii) What would be the explanation given by the physics teacher ?
Answer» (i) Observation, eagerness to learn. (ii) Both the legs of the bird are at same voltage and hence no current passes; to receive a shock, there must be a potential difference between one part of the body and another; if a person hangs from a high voltage wire without touching anything else, he can be quite safe and would not feel shock.

806.

On our return from an excursion trip in our school, I noticed a bird sitting on a high voltage electric wire. I curiously noticed the bird and found to my surprise that the bird flew off after sometime without any electrical shock. This incident made me think of another incident that took place near my house last week where, a boy, who climbed to take a kite, got severe jolt of electric current. I immediately approached my school physics teacher for an explanation. My teacher explained the effect of electrical current which I told my mother that evening.(i) What are the values associated with the above incident ?(ii) What would be the explanation given by the physics teacher ?

Answer»

(i) Observation, eagerness to learn.

(ii) Both the legs of the bird are at same voltage and hence no current passes; to receive a shock, there must be a potential difference between one part of the body and another; if a person hangs from a high voltage wire without touching anything else, he can be quite safe and would not feel shock.

Discussion

807.	Cyclinder is charged by 10mC. Length of cyclinder is 1km and radius is 1 mm. Surface charge density of cyclinder isA. `1.59xx10^(-4)C//m^(2)`B. `1.59xx10^(-2)C//m^(2)`C. `1.59xx10^(-3)C//m^(2)`D. `1.59xx10^(-5)C//m^(2)`
Answer» Correct Answer - C `q=10mC,l=1km,r=1mm,sigma=?` `sigma=Q/A=(q.l)/(2pirl)=q/(2pir)` `=(10xx10^(-6))/(2xx3.14xx1xx10^(-3))` `=1.59xx10^(-3)C//m^(2)`

Discussion

808.	A combination of capacitors is set up as shown in the figure. The magnitude of the electric field, due to a point charge Q (having a charge equal to the sum of the charges on the `4 mu F` and `9 mu F` capacitors), at a point distance 30 m from it, would equal: A. `240 N//C`B. `360 N//C`C. `420 N//C`D. `480 N//C`
Answer» Correct Answer - C In Fig, `3 muF` and `9 muF` capacitors are in parallel. `:. C_(p) = 3+9 = 12 muF` This combination is in series with `4 muF` capacitor `(1)/(C_s) = (1)/(12) + (1)/(4) = (1)/(3), C_(s) = 3 muF` `Q = CV = 3xx8 = 24 muC` This is charge distributies iteself in the direct ratio of capacitros `3 muF` and `9muF`. `:. Q_(9 muF) = ((24)xx9)/(3+9) = 18 muC` Now `Q_(9 muF) + Q_(4 muF) = 18+24 = 42 muC` Electric field intensity due to `Q = 42 muC` at a distance of `30m` from it `E = (kQ)/(r^(2)) = (9xx10^(9)xx42xx10^(-6))/(30xx30)` `= 420 N//C`

Discussion

809.	The expression for the equivalent capacitance of the system shown in Fig. is (A is the corss-sectional area of one of the planes) : A. `in_(0)A//3d`B. `(3 in_(0)A)/(d)`C. `in_(0)A//6d`D. none of the above
Answer» Correct Answer - D `C_(1) = (in_(0)A)/(d), C_(2) = (in_(0)A)/(2d)` `C_(3) = (in_(0)A)/(3d)` As three condensers are in parallel. Fig `:. C_(p) = C_(1) + C_(2) + C_(3) = (in_(0) A)/(d) + (in_(0) A)/(2d) + (in_(0)A)/(3d)` `C_(p) = (in_(0)A)/(d) [1 + (1)/(2) + (1)/(3)] = (11 in_(0) A)/(6d)` Choice (d) is correct.

Discussion

810.	A particle of mass an charge `q` is projected vertically upwards .A uniform electric field `vec(E)` is acted vertically downwards.The most appropriate graph between potential energy `U` (gravitation plus electrostatic) and height h(`lt lt` radius of earth) is :(assume `U` to be zero on surface of earth)A. B. C. D.
Answer» Correct Answer - A

Discussion

811.	If charge q is induced on outer surface of sphere of radius R, then intensity at a point P at a distance S from its centre isA. inversely proportional to `(S+R)^(2)`B. inversely proportional to `R^(2)`C. inversely proportional to `S^(2)`D. directly proportional to `S^(2)`
Answer» Correct Answer - C `Eprop1/r^(2)" "thereforeEprop1/s^(2)`

Discussion

812.	A point charge q is placed at a distance x from the centre of a conducting sphere of radius R(lt x).(a) How much charge will flow through the switch S when it is closed to ground the sphere? (b) Find the current through the switch S when charge ‘q’ is moved towards the sphere with velocity V.
Answer» Correct Answer - (a). `-(R)/(x)q` (b). `(Rq)/(x^(2))v`

Discussion

813.	What does the below diagrams show?
Answer» 1. Figure (a) shows insulated conductor. 2. Figure (b) shows that positive charge is neutralized by electron from Earth. 3. Figure (c) shows that earthing is removed, negative charge still stays in conductor due to positive charged rod. 4. Figure (d) shows that when rod is removed, negative charge is distributed over the surface of the conductor.

813.

What does the below diagrams show?

Answer»

1. Figure (a) shows insulated conductor.

2. Figure (b) shows that positive charge is neutralized by electron from Earth.

3. Figure (c) shows that earthing is removed, negative charge still stays in conductor due to positive charged rod.

4. Figure (d) shows that when rod is removed, negative charge is distributed over the surface of the conductor.

Discussion

814.	Explain: Atoms are electrically neutral.
Answer» 1. Matter is made up of atoms which in turn consists of elementary particles proton, neutron and electron. 2. A proton is considered to be positively charged and electron to be negatively charged. 3. Neutron is electrically neutral i.e., it has no charge. 4. An atomic nucleus is made up of protons and neutrons and hence is positively charged. 5. Negatively charged electrons surround the nucleus so as to make an atom electrically neutral.

814.

Explain: Atoms are electrically neutral.

Answer»

1. Matter is made up of atoms which in turn consists of elementary particles proton, neutron and electron.

2. A proton is considered to be positively charged and electron to be negatively charged.

3. Neutron is electrically neutral i.e., it has no charge.

4. An atomic nucleus is made up of protons and neutrons and hence is positively charged.

5. Negatively charged electrons surround the nucleus so as to make an atom electrically neutral.

Discussion

815.	What is the relation between dielectric constant and electric suseptibillity ?
Answer» `K = 1 + chi` where K is dielectric constant and `chi` is electrical susceptibility.

Discussion

816.	Why does the electric field inside a dielectric decrease when it is placed in an external field ?
Answer» It is because the dielectric gets polarised.

Discussion

817.	Figure shows some equipotential lines distributed in space. A charged object is moved from point `A` to point `5`. A. The work done in Fig. (i) is the greatestB. The work done in Fig. (ii) is least.C. The work doen is the same in Fig. (i), Fig. (ii) and Fig. (iii)D. The work done in Fig. (iii) is greater than Fig. (ii) but equal to that in Fig. (i)
Answer» Correct Answer - C In Fig, we observe that in all the three parts, `V_(A) = 20V` and `V_(B) = 40 V`. Work done in carrying a charge `q` from `A` to `B` is `W = q (V_(B) - V_(A))` = same in all the three figures. Choice (c ) is correct.

Discussion

818.	A positively charged particle is released from rest in a uniform electric field. The electric potential energy of the charge.A. remains a constant because the electric field a uniformB. increases becauses the charge moves along the electric fieldC. decreases because the charge moves along the electric fieldD. decreases because the charge moves opposite to the electric field
Answer» Correct Answer - C In a uniform electric field, when a positively charged particle is releases from rest, It moves along the electric field (i.e., from higher potential to lower potential). Therefore, electric potential energy of charge decreases. Choice (c ) is correct.

Discussion

819.	In the above question, the surface charge densities have the correct relation is-A. `sigma_(A) gt sigma_(B) gt sigma_(C) gt sigma_(D)`B. `sigma_(A)=sigma_(B)=sigma_(C)=sigma_(D)`C. `sigma_(D) gt sigma_(C) gt sigma_(B) gt sigma_(A)`D. `sigma_(C) lt sigma_(B) gt sigma_(A) gt sigma_(D)`
Answer» Correct Answer - A

Discussion

820.	Two positively charged balls having mass m and 2 m are released simultaneously from a height h with horizontal separation between them equal to `x_0`. The ball with mass 2 m strikes the ground making an angle of `45^@` with the horizontal. (a) At what angle, with horizontal, the other ball hits the ground? (b) Find the work done by the electrostatic force during the course of fall of the two balls.
Answer» Correct Answer - (a) `theta=tan^(-1)((1)/(2))` (b). `6mgh`

Discussion

821.	Is vacuum the best dielectric, meaning is its dielectric strength infinite ?
Answer» In principle, an absence of particles mean no breakdown. However, practical vacuum still has large number of particles of residual gases. In practice, only pressures lower than 10^-2 mbar can be considered to provide a real dielectric insulation. In such vacuum, free electrical charges under a sufficiently high force can produce ionization and breakdown of its insulation properties. Thus, the dielectric strength of vacuum is only about 20 kV/mm, better than air but lower than most solid dielectrics.

Discussion

822.	How does the electric field inside a dielectric decrease when it is placed in an external electric field?
Answer» Suppose a rectangular slab of dielectric is placed in an electric field , with two of its parallel sides perpendicular to the field. The dielectric becomes polarized. Polarization charges appear on the external surfaces of these two parallel sides such that within the dielectric the field due to the polarization charges is opposite to . Thus, the magnitude of the net electric field within the dielectric is less than , where k is the relative permittivity (dielectric constant) of the dielectric.

Discussion

823.	What is a dielectric? State its two types. Give two examples in each case.
Answer» A dielectric is an electrical insulator i.e., a nonconducting material, that can be polarised by an applied electric field which slightly displaces the positive and negative charges of each molecule. A dielectric can sustain a high electric field up to a certain limit. An ideal dielectric has no free charges. Important commercial dielectrics are of two types, polar and nonpolar. Examples : Polar dielectrics : Silicones, halogenated hydrocarbons. Nonpolar dielectrics : (1) Solid : Ceramics, glasses, plastics (polyethylene, polystyrene, etc.) mica, paper. (2) Liquid : Mineral oils.

823.

What is a dielectric? State its two types. Give two examples in each case.

Answer»

A dielectric is an electrical insulator i.e., a nonconducting material, that can be polarised by an applied electric field which slightly displaces the positive and negative charges of each molecule. A dielectric can sustain a high electric field up to a certain limit. An ideal dielectric has no free charges.

Important commercial dielectrics are of two types, polar and nonpolar.

Examples : Polar dielectrics : Silicones, halogenated hydrocarbons.

Nonpolar dielectrics :

(1) Solid : Ceramics, glasses, plastics (polyethylene, polystyrene, etc.) mica, paper.

(2) Liquid : Mineral oils.

Discussion

824.	What is the bond angle and bond dipole moment of a water molecule?
Answer» In a water molecule, the bond angle between the two O-H bonds is 104.5° and the dipole moment (known as the bond dipole moment) is about 6.17 × 10^-30C∙m [Note: The SI unit of dipole moment, the coulomb-metre is too large at molecular level. Hence, bond dipole moments are commonly expressed in the CGS unit, the debye (D); 1 D = 3.335 × 10^-30 C m. So, the bond dipole moment of a water molecule is 1.85 D while that of HF, NH₃ and HCl are 1.82 D, 1.47 D and 1.08 D, respectively.]

824.

What is the bond angle and bond dipole moment of a water molecule?

Answer»

In a water molecule, the bond angle between the two O-H bonds is 104.5° and the dipole moment (known as the bond dipole moment) is about 6.17 × 10^-30C∙m

[Note: The SI unit of dipole moment, the coulomb-metre is too large at molecular level. Hence, bond dipole moments are commonly expressed in the CGS unit, the debye (D); 1 D = 3.335 × 10^-30 C m. So, the bond dipole moment of a water molecule is 1.85 D while that of HF, NH₃ and HCl are 1.82 D, 1.47 D and 1.08 D, respectively.]

Discussion

825.	The potential energy of a dipole iii a uniform electric held is minimum when the dipole moment is (A) transverse to (B) parallel to (C) antiparallel to (D) either parallel or antiparallel to .
Answer» Correct option is (B) parallel to

Discussion

826.	The ratio of the time periods of small oscillation of the insulated spring and mass system before and after charging the masses is A. `ge 1`B. ` gt 1`C. `le 1`D. `=1`
Answer» In equilibrium of the charged small bodies `(1)/(4piepsilon_(0))(q^(2))/((l_(0)+x_(0))^(2))=kx_(0)` where `x_(0)` is the elongation in the spring in equilibrium. Let a further small elongation of `x` is given to the spring. Then net restoring force on any of the charged particle is given by, `F=-[k(x_(0)+x)-(1)/(4piepsilon_(0))(q^(2))/((l_(0)+x_(0)+x)^(2))]=-kx`. Since `x lt lt x_(0)` `rArr a=-(2k)/(m)x` As `F=mua`, where reduced mass `mu=(mxxm)/(m+m)=(m)/(2)` `rArr a=-omega^(2)x`, Hence `omega=sqrt((2k)/(m))rArrT=2pisqrt((m)/(2k))` In absence of charge, `T_(0)=2pisqrt((m)/(2k))` Therefore `(T)/(T_(0))=1` `:. (D)`

Discussion

827.	Match the field lines given in Column I with charge configuration due to which field lines exist in Column II.
Answer» Correct Answer - A::B::C::D

Discussion

828.	A metallic solid sphere is placed in a uniform electric field, Fig. Which path is followed by the lines of force ?
Answer» When a solid conducting sphere is placed in a uniform electric field `vec(E)` , free electrons of the conductor move in a direction opposite to `vec(E)` . This results in the development of some negative charge on the left part of the sphere and an equal positive charge on right part of the sphere. Electric lines of force end normally on left part, and start normally from the right part. Therefore, path 4 is correct Fig.

Discussion

829.	A charged particle of mass m and charge q is released from rest the position `(x_0,0)` in a uniform electric field `E_0hatj`. The angular momentum of the particle about origin.A. is zeroB. is constantC. increases with timeD. decreases with time
Answer» Correct Answer - C `L=mv_(_\|_)=m(at)(x_0)` `=m((qE_0)/m)t(x_0) or Lpropt`

Discussion

830.	A charge `+Q` is uniformly distributed in a spherical volume of radius R. A particle of charge `+q` and mass m projected with velocity `v_0` the surface of the sherical volume to its centre inside a smooth tunnel dug across the sphere. The minimum value of `v_0` such tht it just reaches the centre (assume that thee is no resistance on the particle except electrostatic force) of he sphericle volume isA. `sqrt((Qq)/(2piepsilon_0mR))`B. `sqrt((Qq)/(piepsilon_0mR))`C. `sqrt((2Qq)/(piepsilon_0mR))`D. `sqrt((Qq)/(4piepsilon_0mR))`
Answer» Correct Answer - D `U_i+K_i=U_f+k_f` `or qV_i+1/2mv_(min)^2=qV_f+0` `=or q(1/(4piepsilon_0))(Q/R)+1/2mv_(min)^2+q[3/2xxQ/(4piepsilon_0R)]` from here we can find `v_(min)`

Discussion

831.	A conducting sphere of radius `R` is given a charge `Q`. The electric potential and the electric field at the centre of the sphere respectively areA. `(Q)/(4 pi epsilon_(0) R)` and zeroB. `(Q)/(4 pi epsilon_(0) R)` and `(Q)/(4 pi epsilon_(0) R^(2))`C. both are zeroD. zero and `(Q)/(4 pi epsilon_(0) R^(2))`
Answer» Correct Answer - 1

Discussion

832.	What is the number of electric lines lines of force that radiate outwards from one coulomb of charge in vacumm ?
Answer» From `phi = (q)/(in_(0))` , when q = 1C `phi = (1)/(8.85xx10^(-12)) = 1.13xx10^(11)`

Discussion

833.	A soap bubble is given a negative charge, then its radiusA. decreasesB. increasesC. remains unchangedD. noting can be predicted
Answer» Correct Answer - B

Discussion

834.	A soap bubble is given a negative charge, then its radiusA. decreasesB. increasesC. remains unchangedD. nothing can be predicted as information is insufficient
Answer» Correct Answer - 2

Discussion

835.	What is the number of electric lines lines of force that radiate outwards from one coulomb of charge in vacumm ?A. `1.11 xx 10^(11)`B. `1.11 xx 10^(-10)`C. `1.1 xx 10^(19)`D. `1`
Answer» Correct Answer - 1 Number of lines `= (q)/(in_(0)) = (1)/(8.85 xx 10^(-12)) = 1.11 xx 10^(11)`

Discussion

836.	A soap bubble of radius R = 1 cm is charged with the maximum charge for which breakdown of air on its surface does not occur. Calculate the electrostatic pressure on the surface of the bubble. It is know that dielectric breakdown of air takes place when electric field becomes larger then `E_(0)=3xx10^(6)W//m`
Answer» Correct Answer - `P=(1)/(2)epsilon_(0)E_(0)^(2)=39.6N//m^(2)`

Discussion

837.	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. zeroB. `EL^(2)`C. `EL^(2)//(2epsi_(0))`D. `EL^(2)//2`
Answer» Correct Answer - A

Discussion

838.	A conducting sphere of radius R is cut into two equal halves which are held pressed together by a stiff spring inside the sphere. (a) Find the change in tension in the spring if the sphere is given a charge Q. (b) Find the change in tension in the spring corresponding to the maximum charge that can be placed on the sphere if dielectric breakdown strength of air surrounding the sphere is ` E_0`.
Answer» Correct Answer - (a). `F=(Q^(2))/(32pi epsilon_(0)R^(2))` (b). `F=(piepsilon_(0)E_(0)^(2)R^(2))/(2)`

Discussion

839.	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. zeroB. `EL^(2)`C. `EL^(2)//(2 epsilon_(0))`D. `EL^(2)//2`
Answer» Correct Answer - 1 `phi = vec(E ). vec(S) = E hat(i) .(L^(2))/(2) hat(j) = 0`

Discussion

840.	Surface tension of a soap solution is T. There is a soap bubble of radius r. Calculate the amount of charge that must be spread uniformly on its surface so that its radius becomes 2r. Atmospheric pressure is `P_0`. Assume that air temperature inside the bubble remains constant.
Answer» Correct Answer - `8pir^(2)[epsilon_(0)(7P_(0)+(12T)/(r)]^(1//2)`

Discussion

841.	Figure shows equi-potential surfa es of the balbeled points point will an electron have the highest potential energy ?.A. Point `A`B. Point `B`C. Point `C `D. Point `D`
Answer» Correct Answer - B

Discussion

842.	The effective capacity between A and B in the figure given is (in`muF`) A. `43/24`B. `24/43`C. `43/12`D. `12/43`
Answer» Correct Answer - B `1/C_(S)=5/6+1/8+5/6=(40+6+40)/48=86/48=43/24`

Discussion

843.	In figure (below) the charge on the `1.5muF` capacitor is A. `60muC`B. `90muC`C. `120muC`D. `30muC`
Answer» Correct Answer - C `Q=CV=1.5xx10^(-6)xx80` `=120xx10^(-6)C` `=120muC`

Discussion

844.	The resultant capacity between the points A and B in the adjoining circuit will be - A. CB. 2CC. 3CD. 4C
Answer» Correct Answer - A `C_(AB)=C+C/2+C/2+C/2+C=3C`

Discussion

845.	In the adjoining circuit, the capacity between the points A and B will be - A. CB. 2CC. 3CD. 4C
Answer» Correct Answer - B Given figure is parallel combination of four rows having two condensers in series. `therefore" "C_(AB)=C_(1)+C_(2)+C_(3)+C_(4)` `=C/2+C/2+C/2+C/2` = 2C

Discussion

846.	Refer to network shown in figure. The effective capacitance between a and b is A. CB. `C/2`C. `C/3`D. `C/4`
Answer» Correct Answer - C In figure, `C_(S_1)=C/3, C_(S_2)=C/3, C_(S_3)=C/3` Now" "`C_(P)=C_(S_1)+C_(S_2)+C_(S_3)=C/3+C/3+C/3=C` Now" "C and `C/2` are in series `therefore" "C_(ab)=(CxxC/2)/(C+C/2)=C/3`

Discussion

847.	Consider an evacuated cylindrical chamber of height h having rigid conducting plates at the ends and an insulating curved surface as shown in the figure. A number of spherical balls made of a light weight and soft material and coated with a conducting material are placed on the bottom plate. The balls have a radius `r lt lt h`. Now a high voltage source (HV) is connected across the conducting plates such that the bottom plate is at `+V_0` and the top plate at `-V_0`. Due to their conducting surface, the balls will get charged, will become equipotential with the plate and are repelled by it. The balls will eventually collide with the top plate, where the coefficient of restitution can be taken to be zero due to the soft nature of the material of the balls. The electric field in the chamber can be considered to be that of a parallel plate capacitor. Assume that there are no collisions between the balls and the interaction between them is negligible. (Ignore gravity) Which one of the following statements is correct?A. (a) The balls will stick to the top plate and remain thereB. (b) The balls will bounce back to the bottom plate carrying the same charge they went up withC. (c) The balls will bounce back to the bottom plate carrying the opposite charge they went up withD. (d) The balls will execute simple harmonic motion between the two plates
Answer» Correct Answer - C After colliding the top plate, the ball will gain negative charge and get repelled by the top plate and bounce back to the bottom plate.

Discussion

848.	Three capacitor of capacitance `C(mu F)` are connected in parallel to which a capacitor of capacitance C is connected in series. Effective capacitance is 3.75. then capacity off each capacitor isA. `4muF`B. `5muF`C. `6muF`D. `8muF`
Answer» Correct Answer - B `C_(P)=C+C+C+=3C` Now,`" "C_(S)=(C_(P)*C)/(C_(P)+C)` `therefore" "3.75=(3CxxC)/(3C+C)" "thereforeC=5muF.`

Discussion

849.	Conducting ball of radius a is surrounded by a layer of dielectric having inner radius a and outer radius b. The dielectric constant is K. The conducting ball is given a charge Q. Write the magnitude of electric field and electric potential at the outer surface of the dielectric.
Answer» Correct Answer - `E=(1)/(4pi in_(0))(Q)/(b^(2));V=(1)/(4pi in_(0))(Q)/(b)`

Discussion

850.	A solid spherical conductor of radius R has a spherical cavity inside it (see figure). A point charge q is placed at the centre of the cavity. (a) What is the potential of the conductor? (b) If the charge q is shifted inside the cavity by a distance `Deltax`, how does the potential of the conductor change?(c) How does your answer to the question (a) and (b) change if the cavity is not spherical and the charge q is placed at any point inside it (see figure) (d) Draw electric field lines in entire space in each case. In which case all field lines are straight lines
Answer» Correct Answer - (a). `(1)/(4pi in_(0))(q)/(R)` (b). No change. (c). No change.

Discussion

Explore topic-wise InterviewSolutions in .

In S.I. system, coulomb-meter is unit ofA. electric intensityB. electric potentialC. electric fluxD. electric dipole moment

In the following figure an isolated charged conductor is shown. The correct statement will be - A. `E_(A) gt E_(B) gt E_(C) gt E_(D)`B. `E_(A) lt E_(B) lt E_(C) lt E_(D)`C. `E_(A)=E_(B)=E_(C)=E_(D)`D. `E_(B)=E_(C)` and `E_(A) gt E_(D)`

A family of equipotential surface are shown. The direction of the electric field at point A is along- A. ABB. ACC. ADD. AF

A hollow conducting sphere is placed in an electric field produced by a point charge placed at `P` as shown in figure. Let `V_(A), V_(B), V_(C )` be the potentials at points `A, B and C` respectively. Then A. `V_(C) gt V_(B)`B. `V_(B) gt V_(C)`C. `V_(A) gt V_(B)`D. `V_(A)=V_(B)`

Two point charges +9e and +e ,

Cyclinder is charged by 10mC. Length of cyclinder is 1km and radius is 1 mm. Surface charge density of cyclinder isA. `1.59xx10^(-4)C//m^(2)`B. `1.59xx10^(-2)C//m^(2)`C. `1.59xx10^(-3)C//m^(2)`D. `1.59xx10^(-5)C//m^(2)`

The expression for the equivalent capacitance of the system shown in Fig. is (A is the corss-sectional area of one of the planes) : A. `in_(0)A//3d`B. `(3 in_(0)A)/(d)`C. `in_(0)A//6d`D. none of the above

If charge q is induced on outer surface of sphere of radius R, then intensity at a point P at a distance S from its centre isA. inversely proportional to `(S+R)^(2)`B. inversely proportional to `R^(2)`C. inversely proportional to `S^(2)`D. directly proportional to `S^(2)`

A point charge q is placed at a distance x from the centre of a conducting sphere of radius R(lt x).(a) How much charge will flow through the switch S when it is closed to ground the sphere? (b) Find the current through the switch S when charge ‘q’ is moved towards the sphere with velocity V.

What does the below diagrams show?

Explain: Atoms are electrically neutral.

What is the relation between dielectric constant and electric suseptibillity ?

Why does the electric field inside a dielectric decrease when it is placed in an external field ?

In the above question, the surface charge densities have the correct relation is-A. `sigma_(A) gt sigma_(B) gt sigma_(C) gt sigma_(D)`B. `sigma_(A)=sigma_(B)=sigma_(C)=sigma_(D)`C. `sigma_(D) gt sigma_(C) gt sigma_(B) gt sigma_(A)`D. `sigma_(C) lt sigma_(B) gt sigma_(A) gt sigma_(D)`

Is vacuum the best dielectric, meaning is its dielectric strength infinite ?

How does the electric field inside a dielectric decrease when it is placed in an external electric field?

What is a dielectric? State its two types. Give two examples in each case.

What is the bond angle and bond dipole moment of a water molecule?

The potential energy of a dipole iii a uniform electric held is minimum when the dipole moment is (A) transverse to (B) parallel to (C) antiparallel to (D) either parallel or antiparallel to .

The ratio of the time periods of small oscillation of the insulated spring and mass system before and after charging the masses is A. `ge 1`B. ` gt 1`C. `le 1`D. `=1`

Match the field lines given in Column I with charge configuration due to which field lines exist in Column II.

A metallic solid sphere is placed in a uniform electric field, Fig. Which path is followed by the lines of force ?

A charged particle of mass m and charge q is released from rest the position `(x_0,0)` in a uniform electric field `E_0hatj`. The angular momentum of the particle about origin.A. is zeroB. is constantC. increases with timeD. decreases with time

What is the number of electric lines lines of force that radiate outwards from one coulomb of charge in vacumm ?

A soap bubble is given a negative charge, then its radiusA. decreasesB. increasesC. remains unchangedD. noting can be predicted

A soap bubble is given a negative charge, then its radiusA. decreasesB. increasesC. remains unchangedD. nothing can be predicted as information is insufficient

What is the number of electric lines lines of force that radiate outwards from one coulomb of charge in vacumm ?A. `1.11 xx 10^(11)`B. `1.11 xx 10^(-10)`C. `1.1 xx 10^(19)`D. `1`

Surface tension of a soap solution is T. There is a soap bubble of radius r. Calculate the amount of charge that must be spread uniformly on its surface so that its radius becomes 2r. Atmospheric pressure is `P_0`. Assume that air temperature inside the bubble remains constant.

Figure shows equi-potential surfa es of the balbeled points point will an electron have the highest potential energy ?.A. Point `A`B. Point `B`C. Point `C `D. Point `D`

The effective capacity between A and B in the figure given is (in`muF`) A. `43/24`B. `24/43`C. `43/12`D. `12/43`

In figure (below) the charge on the `1.5muF` capacitor is A. `60muC`B. `90muC`C. `120muC`D. `30muC`

The resultant capacity between the points A and B in the adjoining circuit will be - A. CB. 2CC. 3CD. 4C

In the adjoining circuit, the capacity between the points A and B will be - A. CB. 2CC. 3CD. 4C

Refer to network shown in figure. The effective capacitance between a and b is A. CB. `C/2`C. `C/3`D. `C/4`

Three capacitor of capacitance `C(mu F)` are connected in parallel to which a capacitor of capacitance C is connected in series. Effective capacitance is 3.75. then capacity off each capacitor isA. `4muF`B. `5muF`C. `6muF`D. `8muF`

Conducting ball of radius a is surrounded by a layer of dielectric having inner radius a and outer radius b. The dielectric constant is K. The conducting ball is given a charge Q. Write the magnitude of electric field and electric potential at the outer surface of the dielectric.