CBSE Class 12 Physics Question Paper 2012 (Delhi Set 1)

CBSE CLASS XII Questions

• 1.

  Write two advantages of reflecting telescope over refracting telescope.
  

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• 2.

  Consider a cylindrical conductor of length \( l \) and area of cross-section \( A \). Current \( I \) is maintained in the conductor and electrons drift with velocity \( \vec{v}_d \, (|\vec{v}_d| = \frac{eE}{m} \tau) \), where symbols have their usual meanings. Show that the conductivity of the material of the conductor is given by \[ \sigma = \frac{n e^2 \tau}{m}. \]

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• 3.

  Consider the nuclear reaction \( X \to Y + Z \). Let \( M_x \), \( M_y \), and \( M_z \) be the masses of the three nuclei X, Y, and Z respectively. Then which of the following relations hold true?

  • \( (M_x - M_z)<M_y \)
    
  • \( (M_x - M_y)<M_z \)
    
  • \( M_x>(M_y + M_z) \)
    
  • \( M_x<(M_y + M_z) \)
    
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• 4.

  Two air-filled capacitors of capacitances $C_1$ and $C_2$ are connected in parallel with a dc battery. After the capacitors are fully charged, a slab of dielectric constant K is inserted between the plates of each capacitor. How will the (i) charge on each capacitor and (ii) energy stored in the capacitor affected after the slab is introduced.
  

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• 5.

  Two metal spheres of radii $r_1$ and $r_2$ ($> r_1$) having charges $q_1$ and $q_2$ respectively kept in air, are brought in contact. Which of the following statements is not correct ?
  

  • The total charge of the two spheres is conserved.
    
  • Both spheres attain the same potential.
    
  • The final potential of the system equals $\frac{1}{4\pi\epsilon_0} \frac{(q_1 + q_2)}{(r_1 + r_2)}$
    
  • The final potential of the system equals $\frac{1}{4\pi\epsilon_0} \frac{(q_1 + q_2) (r_1 + r_2)}{r_1 r_2}$
    
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• 6.

  With the help of a labelled diagram, explain the principle, construction and working of an a.c. generator.
  

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