Physics xii

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  1. 1. S.No. ChapterPage1.Electrostatics32.Current Electricity203.Magnetic Effects of Current and Magnetism414.Electromagnetic Induction and Alternating Currents 595.Electromagnetic Waves776.Optics 827.Dual Nature of Matter and Radiation988.Atoms and Nuclei1049.Electronic Devices116 10.Communication Systems 130Sample Papers 137 2 XII Physics
  2. 2. UNIT IWeightage 8 Marks Electric charges, Conversation of charges, Coulombs Law; Force between two points charges, forces between multiple charges, Superposition Principle. Continuous charge distribution. Electric field, electric field due to a point charge electric field lines, electric dipole, electric field due to dipole; torque on a dipole in uniform electric field. Electric flux, statement of Gauss Theorem and its applications to find field due to infinitely long straight wire, uniformly charged infinite plane sheet and uniformly charged thin spherical shell (field inside and outside) Electric Potential, Potential difference, electric potential due to a point charge, a dipole and system of charges, equipotential surfaces, electrical potential energy of a system of two point charges and of electric dipole in an electrostatic field. Conductors and Insulators, free charges and bound charges inside a conductor, Dielectric and electric polarization, Capacitors and Capacitance, combination of capacitances in series and parallel. Capacitance of a parallel plate capacitor with or without dielectirc medium between the plates energy stored in a capacitor, Van de Graff Generator. Physical QuantityFormulae Used SI UnitQuantization of charge q = ne C Kq1q2Coulombs forceFN r2Kq1q2 Kq1q 2 In vector fromF12 2r 21r21 r 21 r 321F0 mCm 0 E0Dielectric constant (or relative permitivity)KD rFm 0C0 m Em rHence F0 Fm as free space has minimum permittivity3 XII Physics
  3. 3. qLinear charge density Cm1LqSurface charge densityCm2AFElectric field due to a point chargeELt theoreticalq0 0 q0Kq1 Innumerical, we useEr2 1 qx1qyThe components of electric field, Ex,E y ,NC1 4 0 r34 0r3 1 qzTorque on a dipole in a uniform electric fieldEz Nm 4 0 r3 Electric dipole moment p E or pE sin Cm Potential energy of a dipole in a unifor electric fieldP q 2a or pq 2aJ U p El or U pE cos 1 2prEaxial 2 4 E0r a2 2Electric field on axial line of an electric dipoleNC1 1 2pWhen 2a r,Eaxial 4 E0 r 31 q 2aEequatorial 3 40Electric field on equatorial line of an electric dipoler 2 a2 2 1 pWhen 2ar,Eequatorial 4 E0 r 3 dVElectric field as a gradient of potentialE drWABElectrical potential differences between points A & BVB VAVolts (or JC1) q0 1 q WElectric potential at a pointVA 4 E0 rA q 1 n qiElectric potential due to a system of chargesV 4 E0 i 1 riElectric potential at any point due to an electric dipole1 P cos V 4 E0 r 2 a2 cos2 1p When, 0 or77, V 4 E0 r 2 a 21 p If ra, V4 E0 r 2 When, 90 , Vequi 0 4XII Physics
  4. 4. Total electric flux through a closed surface S E.dS EndS Nm2 C1q= E Effective Area = E 0 1Electric field due to line chargeE NC1(or V/m)20 rElectric field due to an infinite plane sheet of chargeE20Electric field due to two infinitely charged plane parallel E 0sheetsR2Electric field due to a uniformly charged spherical shell E0r2 Whenr R,0 02 Whenr R, E 4 r 0qElectrical capacitance CF(SI Unit) F (Practical Unit)VCapacitance of an isolated sphere C 4 0rA 0Capacitance of a parallel plate Cd1 1 1 1Capacitors in seriesC C1 C2C3Capacitors in parallelC = C1 + C2 + C30ACapacitance of a parallel plate capacitor with dielectric C 1d t 1KDslab between plates C0Capacitance of a parallel plate capacitor with conducting C t1slab between platesdq21 1Energy stored in a charged capacitorU CV2 qV J2C2 2 Resultant electric field in a polarised dielectric slabEE0E p, where Cm1 E 0 = Applied electric field and E p = Electric field due to polarizationPolarization densityP = n E = EVm1 or Nc1Dielectric constant (in terms of electric susceptibility or KD = 1 +atomic polarisability)5XII Physics
  5. 5. q 1 1Potential difference between inner and outer shell in Vr0 VRVolts (or JC1) 4 Eo ro Rvan de Graaff generator 1. Draw schematically an equipotential surface of a uniform electrostatic field along X axis. 2. Sketch field lines due to (i) two equal positive charges near each other (ii) a dipole. 3. Name the physical quantity whose SI unit is volt/meter. Is it a scalar or a vector quantity? 4. Two point charges repel each other with a force F when placed in water of dielectric constant 81.What will the force between them when placed the same distance apart in air? Ans. : (81F) 5. Electric dipole moment of CuSO4 molecule is 3.2 1032 Cm. Find the separation between copperand sulphate ions. Ans. : (103m) 6. Net capacitance of three identical capacitors connected in parallel is 12 microfarad. What will bethe net capacitance when two of them are connected in (i) parallel (ii) series? Ans. : Cp = 8 f Cs = 2 f 7. A charge q is placed at the centre of an imaginary spherical surface. What will be the electric fluxdue to this charge through any half of the sphere. Ans : q/2 0 8. Draw the electric field vs distance (from the centre) graph for (i) a long charged rod raving linearcharge density < 0 (ii) spherical shell of radius R and charge Q > 0. 9. Diagrammatically represent the position of a dipole in (i) stable (ii) unstable equilibrium whenplaced in a uniform electric field.10. A charge Q is distributed over a metal sphere of radius R. What is the electric field and electricpotential at the centre? Ans. : E = 0, V = kQ/R11. If a body contains n1 electrons and n2 protons then what is the total charge on the body? Ans. : (n2 ~ n2)e12. What is the total positive or negative charge present in 1 molecule of water. Ans. : 10e.13. How does the energy of dipole change when it in rotated from unstable equilibrium to stableequilibrium in a uniform electric field.Ans. : decreases14. Write the ratio of electric field intensity due to a dipole at apoint on the equatorial line to the fieldat a point at a point on the axial line, when the points are at the same distance from the centreof dipole.15. Draw equipotential surface for a3 dipole.16. An uncharged conductor A placed on an insulating stand is brought near a charged insulatedconductor B. What happens to the charge and potential of B?Ans : charge same, p.d. decrease6XII Physics
  6. 6. 17. A point charge Q is placed at point O shown in Fig. Is the potential difference VA VB positive,negative or zero, if Q is (i) positive (ii) negative charge.Ans : When Q is + ive. VAVB > 0When Q is ive, VAAB < 0O AB18. An electron and proton are released from rest in a uniform electrostatic field. Which of them willhave larger acceleration?Ans : ae > ap19. In an uniform electric field of strength E, a charged particle Q moves point A to point B in thedirection of the field and back from B to A. Calculate the ratio of the work done by the electricfield in taking the charge particle from A to B and from B to A.Ans : 1 : 120. If a dipole of charge 2C is placed inside a sphere of radius 2m, what is the net flux linked withthe sphere.Ans : Zero21. Four charges + q, q, +q, q are placed as shown in the figure. What is the work done in bringinga test charge fromto point 0. +q +qA Bq0Oq+qD CAns : Zero23. If the metallic conductor shown in the figure is continuously charged from which of the pointsA,B,C or D does the charge leak first. Justify.Ans : A24. What is dielectric strength? Write the value of dielectric strength of air. Ans : 3x106 Vm125. Two charge q and +q are located at points A (0, 0, a) and B(0, 0, +a). How much work is donein moving a test charge from point (b, 0, 0) to Q (b, 0, 0)?Ans : Zero26. If an electron is accelerated by a Potential difference of 1 Volt, Calculate the gain in energy in Jouland electron volt.27. Draw schematically the equipotential surface corresponding to a field that uniformly increases inmagnitude but remains in a constant (say z) direction.28. What is the work done in rotating a dipole from its unstable equilibrium to stable equilibrium? Doesthe energy of the dipole increase or decrease? 1. An oil drop of mass m carrying charge Q is to be held stationary in the gravitational field of theearth. What is the magnitude and direction of the electrostatic field required for this purpose? Ans : E = m8/Q, doninward.7XII Physics
  7. 7. 2. Find the number of field lines originating from a point charge of q = 8.854 C.Ans : d = 10 NC1 m2 3. If q is the positive charge on each molecule of water, what is the total positive charge in (360g)a Mug of water. 360Ans : q 6.0210 23 C 18 4. Derive an expression for the work done in rotating an electric dipole from its equilibrium positionto an angle with the uniform electrostatic field. 5. Show that there is always a loss of energy when two capacitors charged to different potentialsshare charge (connected with each other). 6. A thin long conductor has linear charge density of 20 C/m. Calculate the electric field intensityat a point 5 cm from it. Draw a graph to show variation of electric field intensity with distance fromthe conductor.Ans. : 72 x 105 N/C 7. What is the ratio of electric field intensity at a point on the equatorial line to the field at a pointon axial line when the points are at the same distance from the centre of the dipole?Ans : 1:2 8. Show that the electric field intensity at a point can be given as negative of potential gradient. 9. A charged metallic sphere A having charge qA is brought in contact with an uncharged metallicsphere of same radius and then separated by a distance d. What is the electrostatic force betweenkq2 Athem. Ans :4d210. An electron and a proton fall through a distance in an uniform electric field E. Compare the timeof fall.11. Two point charges q and +q are placed 2l metre apart, as shown in fig. Give the direction ofelectric field at points A,B,C and D. D BqA+q C12. The electric potential V at any po