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ASSIGNMENT 1

ELECTROSTATIC AND CAPACITANCE.[PREPARE (PHYSICS) EXAMINATION THROUGH PREVIOUS YEARS QUESTIONS

OF CBSE MARKED WITH STARS ( )]

THESE QUESTIONS ALSO APPEARED OFTEN IN QUATERLY, HALFYEARLY ANDPRE-BOARD EXAINATION S OF DIFFERENT PUBLIC SCHOOLS OF DELHI

(Generally five-, three-, two- and one- marks questions are generated from the

theory and derivation part of the questions mentioned below including finalformula)

1. Mention two properties of electric lines of force. Why the electric field lines nevercross each other?**** Draw the electric field lines due to a uniformly charged thin

spherical shell when charge on the shell is (i) positive and (ii) negative.*** Setch

lines of force due to two e!ual positive charges placed at a small distance apart in

air. Define dielectric constant.

What is e!uipotential surface?***** Setch lines of force due to a isolated positivepoint charge and draw e!uipotential surfaces. Draw an e!uipotential surface for a

system consisting of two charges Q , -Qseparated "y a distance rin air.* Draw ane!uipotential surface in a uniform electric field.*******#an two euipotential

surfaces intersect each other ? $ive reason.(CBSE 2009)

%he electric field Edue to a point charge at any point near it is defined asE& limqoF'q where q is the test charge and Fis the force acting on it. What is the

physical significance of limqoin this epression?**** Define electric field

intensity. Write its S unit.

Derive an epression for the electric field intensity at any point along the aial line

of an electric dipole. #alculate the electrostatic field intensity at a distant point

situated (i) on the ais and (ii) along the e!uatorial line of an electric dipole.

+. Define electric flu. Write its S unit. State $auss theorem and prove it

.What is the shape of the $aussian surface. Setch lines of force due to a

isolated positive point charge and draw e!uipotential surfaces. ,sing this

theorem prove that no electric field intensity eists inside a hollow charged

conducting sphere.

-pply this theorem for finding (i) the electric field intensity due to a uniformlycharged spherical shell (ii) the electric field intensity due to non conducting charged

solid sphere (iii) the electric field intensity due to a thin infinite sheet of

charge(iv) the electric field intensity due to two thin infinite parallel sheetsof chargeand (v)the electric field intensity due to an infinitely long straight wire

of linear charge density #'m. Draw graphs "etween electric field and distance in

case (i) and (ii).

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. Define electric dipole moment. What is S. unit?

Derive an epression for tor!ue produced "y electric dipole when it is place in

uniform electric field.What is the net force acing on the dipole in this case.

$ive the condition for sta"le e!uili"rium and unsta"le e!uili"rium. What happens

when the dipole is placed in non uniform electric field? Derive an epression for

potential energy of electric dipole placed in uniform electric field.

/. 0riefly eplain the principle of capacitor. Define the term dielectric

constant of a medium in terms of capacitance of a capacitor. (CBSE 2006)

plain the phenomenon when a conducting sla" of thicness t ( t < d)is inserted"etween the plates of a capacitor. 2"tain the epressionfor the newcapacitance ofthe capacitor. 3ow you can increase the capacitance up to infinity.

plain the phenomenon when a dielectric sla" of thicness t (t < d)is inserted"etween the plates of a capacitor. 2"tain the epression for the new capacitance of

the capacitor if the separation "etween two plates is dand dielectric constant is k.***

Derive the epression of the energy stored in a parallel plate capacitor of capacitanceCwith air a s medium "etween its plates having charges Qand 4Q. Show that

this energy can "e epressed in terms of electric field as oE2A d'+ whereAis the

area of each plate and d is the separation "etween the plates.

%hree capacitors of capacitances C1, C1,C1are connected (i) in series and in

parallel. Show that the energy stored in the series com"ination is the same as that of

the parallel com"ination.**

5. $ive the principle construction and woring of 6an De $raff $enerator with la"eldiagram. plain why a hollow spherical conductor is preferred for the

accumulation of charge in it. plain corona discharge?

A small se !" #e$% &m'!$a me$&*als7. %wo charges +qandqare located at points -(889+) and 0 (88+) respectively .

3ow much wor will "e done in moving a test charge from pointP(/88 ) to Q(95.8.8) ? (*****CBSE 2009)

:. %wo point charges 4Q, Qare separated "y 1 m in air. #alculate the electrostatic

potential energy of the system of charges taing the values of charges Q & + 189:# (*****CBSE 200+) ;-ns. 1// 189/5. - charge q is placed at the centre of the line

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18. %wo point electric charges of values q, 2qare ept at a distancedapart in air. -

third charge Qis to "e ept along the same line in such a way that the net force

acting on q and2qis @ero. #alculate the position of charge Qin terms ofqand d.(CBSE a P$eB!a$);-ns. X & 8./1d=

11. %wo point chargesq1& 18 189># and q2=18 18

9># are separated "y a

distance 78 cm in airA (i) Bind at what distance form the 1st

charge q1 would theelectric potential "e @ero and (ii)-lso calculate the electrostatic potential energy of

the system. (CBSE 200+);-ns.X& 58 cmC 1895 oule =

1+. #alculate the wor done to dissociate the system of three charges 1.7 18918#1.7 18918# and 1.7 18918# placed on the vertices of a triangle whose sides are 18

cm. (**************CBSE 200+) ;+. 189> =

1. %wo large parallel this metallic plates are placed close to each other. %he plates

have surface charge densities of opposite signs and of magnitude +8 1891+# 'm+.#alculate the electric field intensity (i) in the outer region of the plates and (ii) in the

interior region "etween the plates. (CBSE 200+) ; -ns. n outer region & @eroC in "etweenthe plates & +.+7 E'# =

1/. - uniformly charged conducting sphere of +.5 m in diameter has surface charge

density 188 F#'m+ #alculate the (i) charge on the sphere and (ii) total electric flupassing through the sphere. (CBSE 200+) ; -ns. 1.7 189/ @ero =

15. 2"tain the e!uivalent capacitance of the following

networ of capacitors. -lso determine the charges

and voltage across C4capacitor if the supply voltageis 886.(CBSEa P$eB!a$);-nsA 189>C 158 6 =

17. - networ of four capacitors each of 15 FB capacitanceis connected to a 588 6 supply as shown in the figure.

DetermineA (i) the e!uivalent capacitance of the

networ and (ii) charge on each capacitor.

(****** CBSE+88>and n !r"-#oard)

; -nsA #e!&+8FBC +.5 m# on each capacitor=

1:. Bind the e!uivalent capacity of the parallel capacitor with different dielectrics as

shown "elow (******CBSE ) A