ASSIGNMENT(2012-2013)SUBJECT: PHYSICS

ClASS : XIITOPIC : ELECTRIC POTENTIAL AND CAPACITANCE

ONE MARKS QUESTIONSQ1.Name the physical quantity whose SI unit is

(i) Coulomb/volt(ii) Newton/coulomb.

(iii) Joule/coulombQ2 When kept in an electric field ,does a proton move from lower to higher potential or from higher to lower potential ? [A.I 1997]Q3 .Equipotential surfaces are perpendicular to electric field lines.Why ? [Delhi 1996].Q4 .A charge of 2C moves between two plates maintained at a potential difference of 1 volt .What is the energy acquired by the charge ?Q5. In a parallel plate capacitor ,the capacitor increases from 4μF to 80μF ,on introducing a dielectric medium between the plates .What is the dielectric constant of the medium ? [A.I 1996]Q6.Is it possible for a metal sphere of 1cm radius to hold a charge of 1C ?

.TWO MARKS QUESTIONS

Q7.How does electric potential vary from point to point due to thin charged spherical shell ? Draw a graph showing variation of potential with distance.Q8.How does electric field and electric potential due to a point charge vary with distance from the point charge ? Draw graph to show the relationship.Q9 .Show mathematically that the potential at a point on the equatorial line of an electric dipole is zero.Q10.The electric field and electric potential at any poimt due to a point charge kept in air is 20NC-1 and 10 JC-1 respectively .Compare the magnitude of this charge . [A.I 1996 ,Delhi 2006 ]Q11.What is an equipotential surface ? Show that the electric field at a point on the surface of a charged conductor or just outside it is perpendicular to the surface ? [Delhi 2001 ,A.I 2001C ,2002]

THREE MARKS QUESTIONSQ12.Sketch a graph to show how charge Q given to a capacitor of capacity C varies with the potential difference V.Prove that the total energy stored in a parallel plate capacitor is ½ CV2 . [A.I 2000C]Q13.A parallel plate capacitor with air as dielectric is charged by a d.c source to a potential V.Without disconnecting the capacitor from the source ,air is replaced by another dielectric medium of dielectric constant 10 .State with reason ,how does (i) electric field between the plates ,and (ii) energy stored in the capacitor change . [A.I 2002]

Q14A parallel plate capacitor with each plate of area A and separation d is charged to a potential difference V. The battery used to charge it is then disconnected.A dielectric slab of thickness d and dielectric constant K is now placed between the plates .What change ,If any ,will take place in (i) Charge on the plates ?(ii) Electric field intensity between the plates ?(iii) Capacitance of the capacitor ?

Justify your answer in each case. [Delhi 2007]Q15.Show mathematically that sharing of charges between two capacitors (or conductors) ,is always accompanied with some loss of electrostatic energy.

FIVE MARKS QUESTIONSQ16 .Derive an expression for the energy stored in a parallel plate capacitor.On charging a parallel plate capacitor to a potential V ,the spacing between the plates is halved and a dielectric medium of K= 10 is introduced between the plates ,without disconnecting the d.c source .Explain using suitable expressions ,how the (i) Capacitance(ii) Electric field ,and(iii) Energy density of the capacitor change [A.I 2008]