KENDRIYA VIDYALAYA SANGATHAN
General Instructions
   (i)     All questions are compulsory
   (ii)    Q.N. 1 to 8 carries 1 marks each
   (iii) Q.N. 9 to 18 carries 2 marks each
   (iv)    Q.N. 19 to 27 carries 3 marks each
   (v)     Q.N. 28 to 30 carries 5 marks each

   1. Which physical quantity has its SI unit as (i) c-m (ii) Vm
   2. Sate the phase relationship between the current flowing and voltage applied in an ac circuit
      for (i) a pure resistor (ii) a pure inductor
   3. Draw the block diagram of generalized communication system
   4. What is the shape of the wavefront from light emerging out of a convex lens when a point
      source is placed at its form.
   5. Why soft iron is used in many parts of electrical machines?
   6. A magician during a show makes a glass lens with n =1.47 disappears in a trough of liquid.
      What is the refractive index of the liquid?
   7. In a photo electric effect experiment the following graphs were obtained between the PE
      Current and applied voltage. Name the characteristics of the incident radiation that was kept
      constant in this experiment.


                                          O     applied voltage

   8. A message signal of frequency 10KHz and peak voltage of 10 Volts is used to modulate a
      carrier of frequency 1 MHz and peak voltage of 20 volts. Determine (a) modulation index
      (b) the sidebands produced.
   9. A bulb B and a capacitor C are connected in series to the ac mains as shown.



   The bulb glows with some brightness. How will the glow of the bulb change when a
   dielectric slab is introduced between the plates of the capacitor. Give reasons.

   An air core L and a bulb B are connected in series to the AC mains as shown



   The bulb glows with some brightness. How will the glow of the bulb change if an iron rod is
   inserted in the coil. Give reasons.

10. State the principle of ac generator. Write an expression for the maximum emf produced in it.
11. Find the equivalent capacitance between A & B in following combination.


        A                                                      B


12. A charge enters with a velocity 2 x 10-8m/s into a perpendicular magnetic field of 10-4 Tesla.
    What will be the force experienced by it? What will be the work done by the field on the
13. A right angled crown glass prism with critical angle 41o is placed before an object, PQ, in
    two positions as shown. Trace the paths of the rays from P and Q passing through the prisms
    in two cases.


               Q                90
                                                          90       45

                     (i)                               (ii)
14. Draw the output wave forms for the gates shown below
                   0                                                                Y

15. Show graphically the variation of resistivity with temperature in case of copper and
16. (i) Draw two equipotentials due to a point charge. (ii) What is the amount of workdone in
    moving a 100nC charge between two points 5cm apart on an equipotential surface?
17. Use mirror formula to show that the virtual image formed by a convex mirror is always
    diminished in size and is located between the focus and the pole.
18. A polythene piece is rubbed with wool is found to have a negative charge of 3 x 10-7 C
    (a)Estimate the number of electrons transferred(from which to which) (b) Is there a transfer
    of mass from wool to polythene?
19. Define mass defect and binding energy. Calculate the BE of a helium nucleus(2He4)
    Given: Mass of on1 = 1.0087u, Mass of proton = 1.0073u, Mass of 2He4 = 4.0026u

20. Prove that
    n2 n1 n2  n1
        
     v u       R

    When refraction occurs on a convex spherical surface as light travels from rarer (n1) to
    denser (n2) medium.
21. How can you increase the current sensitivity of a moving coil galvanometer? A
    galvanometer coil has a resistance of 30 and meter shows full scale deflection for a current
    of 2.0mA. Calculate the resistance required to convert it into an ammeter of range 0 to 10A.
22. What is skywave and surface wave propagation of radiowaves? Why is skywave
    communication over large distances not possible by surface wave propagation.
23. State Gauss theorem. Using it, find the strength of electric field at a distance r from the
    center of a conducting sphere of radius R carrying charge Q, where (i) r < R and (ii) r > R.
24. Define mass number(A) of an atomic nucleus. Assuming the nucleus to be spherical give the
    relation between mass number(A) and radius(R) of the nucleus.
    Calculate density of nuclear matter. Radius of nucleus of 1H1 = 1.1 x 10-5 Å
    What is the ratio of the order of magnitude of density of nuclear matter.

   A radioactive nucleus A decays as given below

   If the mass number and atomic number of A1 are 180 and 73 respectively, find the mass
   number and atomic number of A2. The half life of 92U238 against decay is 4.5 x 109 yrs.
   What is the activity of 1g sample of 92U238 ?
     25. Why skywave transmission of electromagnetic waves cannot be used for TV transmissions?
         Identify the part of the electromagnetic spectrum which is
         (i) suitable for radar systems used in aircraft navigation
         (ii) Adjacent to the low frequency end of the electromagnetic spectrum.
         (iii) produced in nuclear reaction
         (iv) produced by bombarding a metal target by high speed electrons.

     26. Draw a labeled diagram of the apparatus used in Davisson and Germer experiment to
         establish the wave nature of electrons. Derive the expression for the de-Broglie wavelength
         of an electron moving under a potential difference of V volt.
     27. A circuit is set up by connecting L = 100mH, C=5F and R = 100 in series. An alternating
         emf of 1502 volt, (500/) Hz is applied across this series combination. Calculate the
         impedance of the circuit. What is the average power dissipated in (a) the resistor (b) the
         capacitor (c) the inductor (d) the complete circuit?
     28. (i) Explain the construction and working of a cyclotron with a neat diagram.
         (ii) Find the maximum KE that can be attained by a charge in a dee of radius R.

        (i) Estimate the magnetic field at any point distance x along the axis of a circular coil of
        radius ‘a’
        (ii) Sketch the magnetic field produced close to the centre of the circular coil.

     29. In young’s double slit experiment (i) Derive the conditions for constructive and destructive
         interference. (ii) Prove the law of conservation of energy.(iii) Locate the position of nth
         bright fringe.
         Explain how a ray of while light be dispersed with the help of ray diagram derive the
         expression for refraction index of material of the prism. What is the speciality of minimum
         deviation position of a ray of light.

     30. What is the function of emitter, base and collector in a transistor? Explain with a circuit how
         can a CE n-p-n transistor works as an amplifier.

        What is rectification? How does a diode be used for rectification? Give the two types of
        rectifiers and explain the working of full wave rectifier showing input and output

                2ND PREBOARD EXAM-2009 PHYSICS-XII
                                    MARKING SCHEME
Q no      Answer                                Marks                   Total
1         Dipole moment                         ½                       1
          Electric flux                         ½
2.        i)  = 0                              ½                       1
          ii)voltage leads const by phase       ½
          angle /2
3.        Block diagram                         1                       1
4.        Plane wave front                      1                       1
5.    Low hysteresis loss &               ½       1
      Higher permeability                 ½
6.    n' = 1.47                           1       1
7.    Frequency                           1       1
8.    Modulation index 0.5                ½       1
      Side bands are at 1010KHz and       ½
      990 KHz
9.    Xc = 1/wc, Xc decreases so bulb     1       1
      glows with more brightness
      XL = wL, XL increases, so bulb      1       1
      glows dimmer
10    Principle                           1       2
      Eo = BAwN                           1
11.   Correct Arrangement                 1       2
      Correct Answer                      1
12.   Force                               1       2
      Work done                           1
13.   Ray direction in (i) & (ii)         1       2
14.   Correct output form                 2       2
15.   Graphs (2)                          1+1     2
16.   Diagrams                            1       2
      Zero                                1
17.   Diagram                             1       2
      Correct Explanation                 1
18.   a&b                                 1+1     2
19.   Mass defect                         1½      3
      B.E.                                1½
20.   Diagram                             ½       3
      Sign convention                     ½
      Steps                               1
      Answer                              1
21.   Correct answer for current          1       3
      Numerical                           2
22    Correct answers                     1+1+1   3
23.   Correct answers                     1+1+1   3
24.   R = RoA1/3                          ½       3
      =3m/4Ro3                          ½
      =2.98 x 1017 kg/m3                 1½
      Mass number definition              ½
25.   (a) Region                          1       3
      (b) Correct Answers to 4 question   4x½
26.   Labelled diagram                    1       3
      Derivation                          2
27.   Z = 2 x 100Ω                       1       3
      (a) IV2R = 225w                     ½
      (b) Pcapacitor = 0                  ½
      (c) Pindent = 0                     ½
      (d) Complete circuit = 225w         ½
      i) Correct answer                     ½+½   3
      ii) 1.23 x 104 Bq                     2
28.   Diagram                               1     5
      Construction                          1
      Working                               1½
      Expression for K.E.                   1½
      i) Correct Expression                 3     5
      ii) Correct expression                2
29    i) Condition                          3     5
      ii) Proof                             1
      iii) Position of nth fringe(bright)   1
      Explanation                           1½    5
      Derivation                            3
      Speciality                            ½
30    Function                              1½    5
      Circuit Diagram                        ½
      Explanation                           3
      Defination                            ½     5
      Reason                                ½+½
      Diagram                               ½
      Explanation                           2

      Output wave form                      1

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