TRACJ<.·RECORD OF CBSE ELECTROSTATICS~'-. ,·. ---:-~ ....

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Coulomb's·Law ,.. C

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Very Short -answer Questions
NUMERICAL EXAMPLES . QI .Name basic properties of electric chargeq _:.•
QI.Two ~dentical metallic spheres, having unequal , - - . (CBSE 96 Comptt.) • • .
opposite chai:ge~ are plac7d at a distance 0.90 m apart in Q2. What is quantization of elecf;ric charge? • ,· •
air . After bnngmg them m contact with each there they - ? (CBSE 92)
. are again placed at the same distance apart. Now the Q3. Calculate the charge carried by 12.5xl01~ electrons.
... force of repulsion betwe~n them is 0.025 N. calculate (CBSE 92)
• the finaLtcharge on each of· them .. Given (1/4 Q4. State Coulomb's law of force in electrostatics~-
• 9 2 2
1t£o)=9xl0 Nm IC . (CBSE 2002 comptt.) (CBSE 94)
·'
. QS.Define SI_unit of electric charge. (CBSE 94)
Q2.Two. similarly and equally charged identical metal • OR
spheres A ~d B repel each other with a force of 2x l o-s Define Coulomb . . (CBSE 92)
N.. A third identical uncharged sphere C is touched with - . .

. A and then placed at the mid-point ·between A and B . Q6.How·. many ··electrons ·will ·have· a· iotal charge "'of 1·
Calculate the net electric force on C. • (CBSE 2003) ·coulomb ? ; - · • ,· . -
. . ' ..
Q3.Two elec~ic charg~s.q and·2q are at~ distance a apart Q7 .The force of attraction befw¢en two point-charges at a
from each other in air. A·_third charge Q is to be placed · distance r apart is F. Whaf;should be the disU\llce apart
along the same line in such .a way that the net force . in the same rriediu·m so that.the·force becomes F/3? •
• acting at q.and also at 2.q itzero. Calculate the position . . , : (CBSE 2000 Comptt·,98)..
·1 of ~~ge Q in terms ofq and a . . •. . • • (CBSE 98) ·Q8.How does the coulomb force between two point -
charges depend upon the dielectric ·constant .of the-
Q4~T~c;, fixed point -ch~ges +4e and +e units ~re. separated intervening rried~um? .' . ' ":~ .... ,.• . (CBSE 2005) ,
'

- ~y a distance a Where should a .third point -charge q be .

•• placed on ~e line joining the t.wo charg~s so that it be in Q9.Force between tow electric point-charges at a distan~e d
. · _equilibrium? In which condition the equilibrium will be' ·_. :_. apart in air. is F. If these charges are kept at the same
stable and.in which unstable ? • • (CBSE 2005) • • distance in Water. (Dielectric- constant 81) how does the
force between· them change ? • • • (CBSE 97)
QS. Two identical point ~barged Q, Q are kept at a distance
•. r apart. A thi.rd point -charge q is placed on the· line: QI0.Defin~ 'dielectric ·consiant' of a medium in tenns of
joining the above two charges such that all the three • • •force·be~_een electric charges: • (CBSE 97)
• charges are in equilibrium . What is the magnitJde, sign - ; C. • •

and position of the third-charge ?(CBSE 2005, 98, 94) .- .·, Qt I.The dielectric constant of a medium is unity. What will
-. • be its permittivity ? • · (CBSE 92)
-
. ~- . .. '

_Q6. Three point-charges of +2µ C, -3µC and -3µC are kept.

: at the vertices· A, and C respectively of an ~uilateral Ql2.Two p·oint-charges ·q 1 and q2 ·pia~ed cl~se to each
triangle of side 20 cm, as showri. What should be the . • . • other _. What is the nature of the force between the
sign ana magnitude of a charge to be placed at the mid- · ·, charges when q1 q2 <0? , •• . , . , (CBSE 2003)
point M of side BC so that the charge at A r~mains in
equilibrium ? (~BSE 2006) Numerical · _,
QI .Calculate the Couloinbian force between a proton and an
electron sep,rated by o.sx·l o-•~ m. .(CBSE 92) .

Q2.Calculate th~ coulomb force between two a~particle and

-2µC -lµC •
e - - . - -..c a proton separated by S.12xt0•.ts m. (CBSB 92) _•
20cm '
Short Answer type Q3.~alculate the electrostatic fo~ce between two a-particles
QI .A polythene piece rubbed with wool is found to have a . separated by 3.2x 1o••s m (CBSB 92)
negative charge of 3.2 xto·7 C.(a)Find the number of
electrons transferred (from which to which) (b) Is there
a transfer of mass from wool to polythene ?
...

INSTRUCTOR VIJAY; SRIVAS1AVA 9336811116 ·, 98939130022

\ .
 • • ., .
:i
I ·j
-
t is thr
sect each due to a point -cha rge placed at its centre. Wha
9. Why two electric lines of force do not inter charge enclosed by the Gaussian surfa ce. If the radiu s0
• (CBS E 2005 , 03, 01 , 92) much flux wouJ,
othe r? the Gaussian surface is double4 , how
12 2 1 2)
point-charges • through the s, 1rface ?(to=8.85x 10· C N· m•
pass
.
QI O.~ketch ~e electric lines of force due to E 95) (CBSE 99)
(1)q<O, (n)q>O. • • (CBS

sys.tern of two .
QI I .Sketch the electric field lines around a Long -Answer Type Usin g thi
rosta tics .
• equal and opposite point -cha rges . -{CBSE 2006) . QI .State Gauss' theorem in elect
ssion for the elect ric fiel,
theorem, derive. the expre
to two point - intensity at a point :
912. Figu re shows electric lines of force due charge.
. charges Qa and Q2 place d at point s A and B respectively . ·i)Due to an infinitely long, thin unifonnly
E 003) . • • (CBS E 2005 , 04) .•
Write the natur e of charges • . (CB straight wire
charg e .
ii)Due to an infinitely large , thin plane sheet_of
(CBSE 2005, 04, 03, 01 comp tt. 01, 96, 95) •
sphe rical shel l.

.-
iii)Due to a uniformly charged thin
. . (CBSE 2004)
·- ·. ·~ . . iv)In side a hollo w ch~g ed cond uctin g sphere (
... (CBSE 2001 comptt. ,.97)
l distance,.
Q13.Two charg Qa and Q2, separated by a smal
es s· inside ;
satisfy the equation q,+q2=0. What does it tell us· about Q2.Show that no. electric field intensity exist
comp tt.) hollow charged conducting sphe re . ..
the char ges? (C~S E 2003 , 2001
• (CBSE 20:03 comptt. 02, 2000) (

E 94, 92) Q3 .State Gaus s' theor em in electrostatics . Apply it to sho\i

Q14.Define electric dipole moment .. • (CBS , the
that , for a uniformly -charged spherical shell C
vanis hes, wher eas outsi de i
electric dipole electric field inside the shell
QIS.Write the SI unit and. qi~e nsio ns of e w~re .conc entra ted at the
- (CB SE, 2003 , 92) the field is as ff. all the charg
• moment {CBS E 2006 , 92) C
centre. •
Cm?
Q 16. Which physical quantity has its SI unit as ·. '

theo rem. Use it ~o find the electric due to: C

(CBSE 92) Q4.State Ga1,1 ss'
uniformly -=charged , non~cond uctin g solid sphere a
at a distance
Ql7. Two point-charges +q and ~ are situated points (u)outside (ii) ·insid e the. sphe re. How the above
from each othe r . At what point s is the resultant electric metallic.? ••.
results would .char ge, if the sphe re were
• field parallel to the line joining the charges
? N
(CBSE 97) Q
Short-Answer :_fype .
Numerical QI.D efine 'elec tric flux' . Give its SI unit.
d at points A
QI.T wo point~harges 3 µC and- 3µC are place . (CBSE 2006).
apart in vacu um. Find the
and B respectively, 20 cm Q2.State Gauss' theorem in elect rosta tics.
point O of the line AB . What
electric field _at the mid- • (CBSE 2004, 03 comptt, Q3 , 96)
rienc ed by a nega tive test-c harge of
• force will be expe res enclosin. Q:
(CBSE 2~03) Q3.Stand S2 are two hollow concentric sphe
l.Sxl0-9 C placed at 0. hat is th
charges Q and 2Q respectively, as show n. (i)W
ow wi'
ratio of the electric flux through S1 ·and S2 .(ii)H
Q2.l f an off drop of weight 3.2x I 0· . N is balanced in
13

the
an
drop. the electric. flux through the. sphere S1 charg e, if Q~
electric field of sx·1os·N c·•,· find the charge on
(CBSE 93) medium or diele~tric constant 5 is introd uced· in th
, (CBS E 2002 )
space inside S1 ~n place of air ?

@,
respect to a
Q3.An electric dipo le, when held at 30° with
uniform electric field of Jo• N/C,
. of 9x I0· N m. Calculate the dipo
dipole .
26
expe
le
rienc
mom
•
es a torque
ent of the
(CBS E 96)
•
is located Q1
Q4.A small metal sphere carrying a charge +Q
Gau ss' Theorem the centre of a spherical cavit y in a large un c
Numerical Exam ples .
metal sphere . as shown . Use Gaus s' theor em to
nnly over a
QI.A charge of 17.7xl0_. C is 2distributed unifo electric fields at points P 1 and 2
p • (CBS E 2006 )
ulate the elect ric field
large sheet of area 200 m .Calc Q2
from it in air . Given :
intensity at a distance2 20 cm
12 1 (C.BS E 2003 Com ptt.)
t:o=8.85xl0" c2N" m· •
2
3
s nonnally
Q2.An elect ric. flux of -6xl 0 Nm /C passe
of radius IO cm ,
through a spherical Gaussian surface

INSTRUCTOR VIJAY SRIVASTAVA 9336811116 ,

 ...... :. . .
•·.:. .• . ..
_

'(i~.WhY two electric lines of fo~e do not intersect each

other? (CBSE 2005 , 03 , 0 l , 92) due to a point -charge placed at its centre. What is the
charge e~closed by the Gaussian surface. If the radius o'r
Qt0.Skctch the elecrric lines of force due to point-charges the Gaussian surface is doubled , how much flux would
(i)q<O, (ii)q>0. • • (CBSE 95) pass through th~ surface ?(to=8.85x 10·12 C2N"1 m·2)
.. (CBSE 99) .
QI I.Sketch the elec.tric ~eld lines ~ound a system of two
equal and opposite pomt ~hargdr . (CBSE 2006) Long -Answer Type
QI .State Gauss' theorerr, in electrostatics . Using this ,
Q12.Figure shows .e!ectric lines o_f force due to two point_ theorem, derive the expression for the electric field
._ charges q, and Q2 placed at pomts A and B respectively.
Write the nature of charges·. (CB E 2003)
!ntensity at a point : · / ,
1)Due to an infinitely long, thin uniformly charged
stra_ight wire .
.·
I
' (CBSE 2005 , 04)
ii)Due to_ an infinitely large, thin plane sheet of charge .
• (CBSE 2005, 04, 03, 01 comptt. 01, 96, 95) .
iii)Due to.a uniformly charged thin spherical shell.
. (CBSE 2004)
QIJ.Two charges·q, and q2, separated by _a smail distance, · iv)In side a hollow charged conducting sphere
• satisfy the equation q,+q2=0. What does it tell us about . . (CBSE 2001 comptt. , 97)
Q2.Show that no electric. field intensity exists inside a
the charges? (CBSE 2003 , 2001 comptt.) . hollow charged conducting sphere~ ..
. (CBSE 2003 comptt. 02, 2000)
1 Q14.Define electric dipole moment. (CBSE 94, 92) Q3.State Gauss' theorem in electrostatics. Apply it to show
that , for a uniformly -charged spherical shell , the
Ql5.Write the SI unit and dim~nsions of electric dipole
electric field inside the shell vanishes, whereas outside it
moment (CBSE , 2003 , 92) the field is as if all the.charge .were con~ntrated at the
centre . . • (9B~.E 2006 , 92)
QI6.Whi~h physical quantity has its SI unit as Cm'?.
••• (CBSE 92) Q4.State Gauss' theorem, Use it to find the electric due to a
Ql 7.Two point-charges +q and -q are situated at a distance. uniformly -e=charged , non-con~µcting solid sphere at
from each other . At what points is the resultant electric • points (u)outside (ii) inside the sphere. How the above
field parallel to the line joining the charges? results would_ c~argt: , if _the sphere were metallic ?
• • (CBSE 97) ·
Numerical Short-Answer Type
QI.Two point-charges 3 µC and -3µC are placed at points A QI.Define 'electric flux' . Give its SI unit. •
and B respectively, 20 cm apart in vacuum. Find the (CBSE 2006) ,
electric field at the mid-point. 0 of the line AB. . What Q2.State Gauss' theor~m in electrostatics. .•
force will be experienced by a negative test-charge of (CBSE 2004, 03 comptt, 03, 96)
l.Sxl0"' C placed at 0. · (CBSE 2003) Q3.S 1and S2 • are two hollow ccncentric spheres enclosing
charges Q and 2Q respectively, as shown. (i)What is the
Q2.lf an oil drop of weight 3.2x l 0-13 N is balanced in an . ratio of the electric flux through S1 an.d .(ii)How will.
electri~ field of Sx 1os N c·•, find the charge on th_e drop. • · the electric flux through the sphere •Sa charge,' if a
• , . (CBSE 93) medium of dielectric constant 5 is introduced in the
Q3.An electric dipole , when held at 30° with. respect to a space inside S1 in. p l @ , (CBSE 2002)
uniform electric field of l 04 N/C, experiences a torque
2
of 9x10· ' N m. Calcut'ate the dipole moment of the
dipole . (CBSE 96)

Gauss' Theorem Q4.A small metal sphere carrying a charge +Q is located at

, Numerical Examples • th~ centre of a spherical cavity in a large un charged
• metal sphere , as shown . Use Gauss' theorem to find
QI.A charge of 17.7xl0-' C is distributed uniformly over a
large sheet of area 200 m2.Calculate the electric field electric fields at points P1 and P2 • (CBSE 2006)
• • • ----
intensity at a distance 20 cm from it in air . Given :
£o1=1.8Sxl0·12 c2N"1 m·1. (CBSE 2003 Comptt.)

Q2.An electric ftux of -6x Io> Nm2/C passes normally • V

through a spherical Oaussian surface of radius 10 cm ,

. INSTRUCTOR VIJAY SRIVASTAVA 9336811116,

- a
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Electric Field :Electric Dipole (CBSE 2002)

Numerical Examples Q 11.An electric dipole is held in a unifonn electric field. (i)
QI .An electron is separated from a proton by a distance of Using suitable diagram , Show that it does not undergo
0.53A. Calculate the electric field at the location of the any translatory motion, and (ii)derive an expression for
electron . (CBSE 92) the torque acting on it and specify its direction .
(CBSE 2006)
Q2.Two point -charges of Sxl0- 19 C ·and 20x10- 19 C are Short Answer Type
separated by a distance of 2 m . At which point on the Qt.Define 'electric line of force'·and give its two important
line joining them , the electric field is zero ? properties . (CBSE 2006)
(CBSE 2001 Comptt.)
Long Answer Type Q2.Two point -charges of unknown magnitudes and signs
Ql .Derive an expression for the intensity of electric field at are placed at a distance apart. The electric field is zero at .
a point distant r from a point charge q. (CBSE 94) a point, not between the ·charges , but on the line joining
them. Write two essential conditions for this to happen.
Q2. What is meant by an electric dipole ? Derive an • (CBSE 97)
expression_ for the electric field intensity at a distant Q3.ln the given figure are shown the tracks of three charged
point along the axial line of an electric dipole . particles in an uniform electric field .What are the signs
(CBSE 95) of the three charges ? Which particle has the highest
Q3.Define electric dipole moment Derive an expression for charge-to -mass ratio? (CBSE 2001 Comptt.)
the electric field intensity at any point along the •

equatorial line of the dipole. (CBSE 94, 93)

Q4.Derive an expression for the electric field at a point lying

on the equatorial axis of an electric dipole. Hence write
the expression for the electric field due to a small
electric dipole at a far off point . (CBSE 2006) Q4.An electric dipole is held at an angle 8 in a uniform
. .
external electric_ field !. Will •there be any (i)net
QS-.Define electric field at a point . Two point -charges q translatory force , (ii) torque acting on it ? Explain what
and -q are placed at a distance 2a apart. Calculate the happens to the ~ipole on being released .
electric field at a point'P situates at a distance r along (CBSE 94)
the perpendicular bisector of the line joining the charges Very Short- Answer Jype •
•. What is the field when r>>a ? (CBSE '93) •
Q 1. Define electric field Eat a point i~ space .
Q6.Define electric field intensity . Write its SJ. unit . Write (CBSE 92)
-the magnitude and direction of electric field intensity Q2. Which physical quantity has unit NC-'?Is it a vector or a
due to an electric dipole of length 2a at the mid -point scalar quantity? (CBSE 2002 Comptt.)
of the line joining the two charges (CBSE 93) • '
Q3. Write SI unit and dimensions of electric field .
(CBSE 2003,92)
Q7.Define· dipole moment of an electric dipole • Show Q4. \Yhat is an electric line of force ? (CBSE 2003)
mathematically that the electric field intensity due to a
short dipole at a distance 'r' along the axial line is twice Q5.Mention a·ny two properties of electric lines of force .
..
I the intensity at the same distance along the equatorial Sketch thetn for isolated positive arid negative point-
line . (CBSE 99) charges . (CBSE 2003 , 92)

QB.Show that in a unifonn electric field , a dipole Q6.Sketch lines of force due to :
experiences a torque but ·no net force . Derive i)Two equal, positive point -charges separated by a
expression for the torque . (CBSE 98, 97 , 92) small •distance ,
ii)A positive and an equal negative point -char&,"!
Q9.·What is an electric dipole TD~rive an expre_ssion f~r the separated by a small distance. (CBSE 2003)
torque acting on an electric dipole placed m a umform
electric field . H~nce define dipole .:..moment . Q7.Draw iines of force to'represent a unifonn ele~tric field
(CBSE 2003 comptt.) . (CBSE ,95, 92)
QI O.Define the tenn electric dipole !11oment.. Give it~ unit. QB.An electrostatic field line is a continuous curve, that is ,
Derive an expression for the•max1mum torque .~ctmg on it cannot have sudden discontinuities . Why ? . -
an electric dipole, wh~n held in a uniform electric field . (CBSE 2005)

INSTRUCTOR VIJAY SRIVASTAVA 9336811116, 9839130022

2
 ,
,

;" V~ Short-Answer Ty~e . Q7.An _electric dipole of length 4 cm, when placed ·with its
Qlj,hich physical. quantity has SI umt as Vm. axis making an angle of 30° with a uniform electric field
experiences a torque of 4 Nm. Calculate .the
I
(CBSE 92)
Q2.An electric dipole of, dipole moment 20 x Io-<> C-m is (i)magnitud~ of the electric field, (ii)potential energy of.
enclosed by a surface .What is the net flux coming out the dipole, if the has charges of ±10 nC. (CBSE 2004-)
ofthe surface·. .(CBSE 2006)
Numericals
QI .A spherical Gaussian surface encloses a charge of Long-Answer Type ,
8.85x IO.a. C.(i)Calculate electric flux passing through QI .Define electric potential . Derive an expression for the
the surface ..(ii) If .the radius of the Gaussian surface is electric potential at adistance r from a point-charge q.
(CBSE 200 I)
'
(CBSE 2001, 93)
doubled, ·how would the flux charge ?
Q2.Derive an expression for the electric potential at a point
along the axial line of an electric dipole .
Q2.A point charge Q is kept in free space at the centre of a (CBSE 2001,02 comptt.)
cubic Gaussian surface of side /. What is electric flux
. through one of its faces ? (CBSE 2006) .
Q3.Show mathematically that the potential at a point on the
·Electric Potential equatorial line of an electric dipole is zero.
(CBSE 2001 comptt.)
Numerical Examples tial surface Draw ~e same for a
electric field Q4. What is an equipoten
QI .At a point due to point -charge , the
A

ld.is· always directed

intensity and potential are 32 N c· and 161 c·
1 1 - point-char ge, Show that elecmc,ti~
perpendic ular to an eqµipoten tial·surface ....: • . .
respectively. Calc~late-(~)the distance of the charge from • -~-(CBSE 2001 Comptt)
the point of observation , and (iii)magnitude of the ·electric .·dipole moment Detjve an
• - (CBSE 2000) QS.Define the term.
charge .
yXpres~ion for the total work done in rotating an electric
-
dipole through an angle _8 in a uniform electric field .
. 2
Q2.An infinite plane. sheet of charge density Io-a cm• is (CBSE 95, 93)
far apart are -·
held in air. In.the vicinity of the sheet, how
two equipotential surfaces whose p.d. is 5 V ? Given : Short-~nswer :;fyp~ -: :
eo=8.85xl0·12 C2 N·1 m·2• , (CBSE.99) QI.A point-charge q is placed at o, as shown Is VrVQ 1
positive or negative , when (i) q>0, (ii)q<O . Justify your.
t .
I.
C are • answer (CBSE 2006) i

Q3.Tw·o -point -charges ·of 3xl0-a C and -2xl0.

8
·J
q p
located I5 cm apart . At what point on the line joining .• I.
the two charges is the electric potential zero . •
• (CBSE2b02) .
and a proton are accelerated through the
Q4.Find the potential. at the centre of a square·of 9side m9 Q2.An _a. particle
· same potential. difference . Calculate the ratio of
which carries at its four comer charges +2x I0· C, Ix I0-
(CBSE 96 Comptt.) velocities and linear momenta aquired by them .
C, -2xl0-9 C and +3x10-9 C. (CBSE 2002 comptt.)
Very Short Answer Type
QS.A uniform electric field E of 300 NC-I is directed along 1
and C are three points in the field, having x QI.Name the physical quantity which hasjoulecoulomb· as
-x axis A, b
·it unit. Is it a sc~ar _or a vector quantity ?
and y cocrdinates (In meter ) as shown. Calculate the
potential differences between the points (i)A and 8 (ii)B . · ill • •. (CBSE 03, 2000)

.
and C and (iii) C and A B(4•4> (CBSE 2003)
C(-3,4)
-
92. What 1s an equtpoten ti~ __surface ? (CBSE 2003)

Q3.Draw equipotential surfaces in a unifonn electric field .

•
Q4. Draw equipotential surfaces for a unifonn electric field
."" A(4,I)
pointing along·the +Z axis. . (CBSE 2006)
'0 X
,

. ,
QS. What is the shape of equipotential surfaces for a point -
charge ? (CBSE 95)
Q6.Obtain the energy in joule acquired by an electron beam
when accelerated through a p.d. of 2000 V. How much Q6.~raw electric lines of force and equipotential surfaces
19 for a:
speed will the electron gain ?(e= l.6x I0- C, (CBSE 2000)
31
(CBSE 94) a) point charge q>0
m=9x I0' kg) (CBSE2001)
b)Point charge q<0

INSTRUCTOR VIJAY SRIVA STAVA 93368 il116, 9839130022

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potential energy to be at infinity (ii)Draw

Q7.A unifonn electric field E exists betwee~ two charged equipotential surface of the system (CBSE 2004)
plates. What will be the work done in movmg a charge q
along a closed rectangular path ?(CBSE 2001 Compu.) Q9.An electric dipole of length 2 cm is placed with its axis
making angle of 60° to a unifonn electric field -~f 10'
QS'. What is the ~ork done in moving a charge of 1OµC c·• .If it experiences a torque of N m, calculate
between two points on an equipotential surface ? (i)magnitude of the charge on the dipole, and
(CBSE 2002, 2000, 96) _ (ii)potential energy of the dipole. (CBSE 2000) • •'
Q9.What would be the work done if a point-charge +q' is QI 0.Calculate the voltage needed to balance an oil drop
taJ(en from a point A to C and then from C to B, then canying IO electrons between the plates· of a capacitor S
16
along which path more work will be done ? • mm apart. The mass of the drop is 3xIo·. kg and g= 1O_
. (CBSE 2001 comptt.) ms·2. (CBSE 95 Comptt.)
Q10.An electric dipole of moment p is aligned parallel to a
unifonn electric field E. How much work will be done Capacitors and Dielectrics
by an external agent in rotating the dipole through Numerical examples , •
a)90° b)lSq~ c)39~0 from the direction of field Q1. What is the area of the plates. of a 2-F parallel -plate
.. . . ••. •" (CBSE 1997) capacitor with plate separation of 0.5 m ? Why do
Qi 1.Whit··otiernation of an electric dipole in a unifor:m ordinary capacitors have· capacitances of the order- of
electric field corresponds to its stable equilibrium • microfarads ? (CBSE 90_ Comptt)
(CBSE 2001)
Numericals Q2.A para.llel-plate capacitor with air between the plates-ha
Ql.61 work done in moving a positive charge of 3_ C a capacitance of 8 pF. What will be the capacitance if
between two points. Find the p.d. between the points • the distance between the plates is _reduced by half, and
the space between them is filled •with a material of
Q2.The electric potential is +50 volt at a distance of 0.9 dielectric·constant K-6? • . (CBSE 2006)
metre from a point-charge q. What are· the magnitude
and sign of q? .. (CBSE
. . 95 comptt.) Q3.A parallel-plate capacitor is to designed with a
voltage rating 1· kV , using a material of dielectric
ti
•' QJ.A wire i~ bent in a circle of radius 10 cm. It is ·given a constant strength about 107 vm·1.For safety we would
ij. charge of 250 µC which. spreads '~n it .• Unifonnly
I: like the field never to exceed say, 10% of the dielectric
What is the electric potential and intensity of field at its• strength . What minimum area of the plates is required
Ii centre? (CBSE 95 comptt.)
:I to have a capacitance of 50 pf ? . (CBSE 2oosi
!1 .
Q4.The electric field at a point due to a point-charge is 20
•

I: NC"1 and the electric potentiai at that point is 10 J C- Q4.A parallel- plate capacitor of capacitance 100 µF is
w 1·.Calculat the distance of the ·point from the charge and charged to 200 V. After dis-connecting it from the
!I.
battery , using an insulating handle, the distance
the magnitude of the charge. . • (CBSE• 96)
b?twe~~ the. plates is doubled . Find (i)potential
d1~ererice,-between the plates, and ?(ii)Energy stored in
QS.Two point- charges of +4µc and -2µC are placed 1 m
apart in air. At what point on the tine joining the .charges·· the capa~1tor , _after the separation between the plates
. is the electrostatic potential zero ? has been mcreased. • (CBSE 2004)
(CBSE 97) •

Q6.5µC charge is placed at ·each comer of a square ABCD QS_.A 10 µF capacitor is charged by a 30 V d.c. supply and
of side cm. Calculate the electric potential at the then con~e~ted across an uncharged 50 µF capacitor.
~ntre O of the square. (CBSE 2002) Calculate (1) the final potential ·difference across the
I
combin~tion , and (ii)The initial and the final energies •
I ·A , B
l. ',' ,,,
~<
,, cj,
How will you account for the difference in energy?
.. (CBSE 2004)
D ' ', C
Q6.An 8µF capacitor C, is charged to a potential difference
Vo= 120 ~ol~. :he charging battery is then removed and
Q7.Find the electric field between two metal plates 3 mm the capacitor is connected in parallel to an uncharged
apart, connected to a 1~-V battci'y. • (CBSE 93) 4µF capacitor C2,as shown .(a) What will be the final
p.d. across the .combi_nation ? (b) What will be the stored
QB.Two point-charges +I0µC and -I0µC are separated by a energy before and after the switch K is pressed ? What
distance of 40 cm in air . (i)Calcu!ate the electrostatic happen to the energy-difference , (CBSE 93)
potential energy of the system ,assuming the zero of the K

INSTRUCTOR
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I plate air capacitor . •
a~lle~ l]-
/ X d y are two parallel-plate capacitors having the
' . (CBSE 03 comptt., 02,0l comp tt, 01~ 200,97)
Q?. sa;: area of plates and same separation betwee~
the How does the energy stored change when air 1s replac
!ates. x has air between the plates and Y contains a ed
by a·medium of dielectric constant K ?Explain _
~i~lectric medium of er=S.
i)Calculate the potential differences between the plates (CBSE 98, 97 comptt.)
Q7.Give the principle of working of a Van de
ofX and Y. Gr~ff
generator. With the help of a labeled diagram, descn

C J.
ii)What is the ratio of electrostatic energy stored in X be
its construction and w<,rking. How is the leakage
dy ? of

:::i:
x v (CBSE 2004} • - charge minimsed from the generator? ·
an •
cans t:::.: : ~7, 96, 93)
"~
. (CBSE 2006)
Q2.Two metallic spheres of radii r1 and r are far apm
Q8.A parallel -plates capacitor has plates each of area a 2 and
and • conne-:ted by a thin wire. Their combined charge is
separation d. The dielectrics of dielectric constants K Q..
Find(i) their common potential , (ii)charge on the sphere
and K2 are filled between the plates in two1
of radius r 1• (CBSE 2006)
arrangements, as shown. Find out the capacitance of the
capacitor in each of the arrangements (a) and (b). Q3.Capacitors P, Q and Reac h have capacity C. A batter
I I
CBSE2006 charges the capacitor P to a potential difference V.
y

=
If
after charging P, the battery is disconnected from it and

00~ - b)I
the charged capacitor P is connected (i) to Q in parall
and (ii) to R in series, then what will be the potential
difference between the plates of Pin the two cases ?
el

Q9.Four capacitors are connected, as shown . Calculate (CBSE 97)

the Q4.A parallel-plate capacitor is charged to a poten
equivalent between the points P and Q. (CBSE 2000) tial
difference V by a d.c. source, and then disco ~ecte
d
from the source. The distance betw~en the capacitor
~---' ~II l~I plates is now doubled. State how (i)electric field
2µF I 3µF SµF I 1-1-~
IOµF between the plates, (ii)capacitance end (iii)energy stored
in the capacitor would change . (CBSE 2006) •
Long Answer Type •
QI.Explain the principle of a capacitor. Derive
an QS.Why does the electric field inside ·a dielectric decrea
expression for the capacitance of a parallel-plate se
when it is placed in an external electric field '?
capacitor. (CBSE 03, 94, 92)
(CBSE 2006)
Q6.A parallel- plate capacitor is charged by a battery
Q2.Define capacitance of a capacitor . Give its SI which
unit. is then disconnected. A dielectric slab is then inserted
Derive the expression for the capacitance of a parallel- to
fill the space between the plates. Explain the changes,
medium of dielectric constant K.
a
plate capacitor whose plates are separated by dielectric
any, that occur in the values of (i)charge on the plates
if
,
(ii) capacitance, (iii) p.d. between the plates , (iv)
(CBSE 2001, 97, 96 ,93) electri_c field between the plates, (v)energy stored in the
Q3. What is a dielectric ? A dielectric slab of thickness
t is capacitor. (CBSE 2004 , 2000)
kept between the plates of a parallel-plate capacitor
Suppose the capacitor plates are horizontal and the
separated by a distance d. Derive expression for the
capacitance for t<d. dielectric slab is released after inserting it at one end
(CBSE 2001 comptt.) of
the capacitor. Describe its motion.
Q4.Derive the expression for the equivalent capacitance
of Q7.A parallel-plate capacitor with air as dielectric is charg
tw~ capacitors of capacitances C and C connected in ed
senes .
1 2 by a d.c. source to a potential V. Without disconnectin
(CBSE 93) g
the capacitor from the source, air is replaced by
a
QS.Three _capacitors of capacitances C , C and C diele~tric medium of dielectric constant 10. State with
1 2 3 are reason, how does (i) the electric field between the plates
connect~ (i) in series, (ii) in parallel. Derive
expressions for the equivalent capacitance for each of and (ii) energy stored in the capacitor chang e?
lhese combinations . (CBSE 94, 92) (CBSE 2002)
Q8.A capacitor is charged to a potential V .The
1 power
supply is disconne~ted and the capacitor is connected
in
INSTRUCTOR VIJAY SRIVASTAVA 9336811116, 9839130022

I
'
 Numerical . .
parallel to another uncharged capacitor. (i)Deri_ve !he Q l •Find the total energy stored m the capacitors in the g·1ven
expression for the common potential of the combmat1on ·network. A
of capacitors . ii)Show that the total ener!?' of the
combination is less than the sum of the energies stored
1 2µF
. I
I

io them before they are connected. (CBSE 93) I

Q9.Three c1pacitors of capacitances C., C2 and C3 are B

connected (i) in series, (ii)in parallel, .Show that the Q2.Two capacitors of capacitances 6µF and 12 µF are
energy stored in series combination is the same as that connected in series with a battery . The voltage across
in parallel combination . (CBSE 2003)
the· 6µF· capacitor is 2V. Compute the total battery
volt.age . ., (CBSE 2006)
Very Short -Answer Type •
QI.Sketch a graph to show the char~e 'Q'_ ac~u~red by. a
capacitor of capacitance 'C' vanes with increase m Q3.A 4µF capacitor is charged by a 200 V supply. It is then I
potential difference V between its plates. (CBSE 2003) disconnected frQrn the supply, and is connected to
another- uncharged- 2µF capacitor. How •much : I •I

Q2.The graph shows the variation of voltage ·V' across the electrostatic energy of the first capacitor is lost in •the
plates. of two capacitors A and B versus increase of fonn of heat and electromagnetic radiation?
ch~ge 'Q' stored_ on them :Which of the two capacitors (CBSE ·2005)
has· higher capacitance ? Give reason for your answer . Q4.Calculate the. capacitance of the capacitor C• in the
• (CBSE 2004) figure, if the equivalent capacitance of the combination • 1
A between A and B is 15 µ F. (CBSE 94) •
/ • 1olµF

A B
Q3. Write the physical quantity having its unit coulomb/volt. 1olµF
.___ /._Is_it.~vector a-scalar-qu~ntity? (CBSE 98)
• ..
. .\.
.. .-_; - ,·..a, •
Q5.Calculate the capacitance C in the given figure. The
Q4.Tw~ co_nducting spheres of same radiug, one hollow and equivalent capacitance of the combination between P
the other solid , are charged to the same potential. and Q is 30 µF: (CBS~ 95)
Which one does cany more c~arge ? 20µF
. (CB.SE 2000 comptt.)
Q5.Two rectangula r metal plates , each of area A, are kept p C 20µF Q
parallel to each other at a distance 'd' apart to form a 0
I .I
parallel-plat~ capacitor·. If the area of each of the plates 20µF
is m(lde three times and their distance of separation
decreased to 1/3 of its initial value, calculate the ratio of Q6.Cakulate the equivalent capacitance of the combinati~n
their capacitances in the two cases . (CBSE 2003) between the points A ,and B , as shown in Fig •
Q6.Three capacitors of equal capacitances when connected
in series. have net capacitance C1; and when connected A
.----41 ·
lµF I
I .
-3µF
2µF
CBSE 02 comptt.)
B

in parallel have net"capacitance C2• What is the value of

Ca/C2. (CBSE 95) ~ - 4 1 ~ t - F_ _,

Q7.Explain the effect of introducing a· dielectric slab

between the plates of a parallel-plates capacitor oh- its
capacitan~. (CBSE 97) • I

II
Q8.In a parallel-plate capacitor, the capacitance increases
. from SµF to S0µF on introducing a dielectric medium I
• . between the plates. What is the dielectric constant of the
medium ? • (CBSE 96) I
I
Q9.Detine ~ielectric constant in tenns of the capacitance of
a capacitor • . (CBSE 2002· comptt., 95)
II
I
11
INSrRUCTOR VIJAY SRIVASTAVA 93368~1116, 983913Q022 . I I

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