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Class 12 Physics_Board Paper

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Chapter 1: Electric Charges and Fields

Class XII – Physics                           Maximum Marks: 40                Time Allowed: 1 Hour 30 Minutes
General Instructions:
  1. This question paper consists of 5 Sections A, B, C, D and E.
  2. All questions are compulsory.
  3. Section A contains 9 multiple choice questions of 1 mark each.
  4. Section B contains 5 questions of 2 marks each.
  5. Section C contains 4 questions of 3 marks each.
  6. Section D contains 1 case-study based question of 4 marks.
  7. Section E contains 1 long answer question of 5 marks.
  8. Use of calculator is not permitted.
  9. Draw neat and labeled diagrams wherever required.

Section – A (MCQ ) (9 × 1 = 9 Marks)

 
    1. The SI unit of electric flux is:
      (a) N C⁻¹
      (b) V m⁻¹
      (c) N m² C⁻¹
      (d) C² N⁻¹ m⁻²
    2. When an electric dipole is placed in a uniform electric field, it experiences:
      (a) Only force
      (b) Only torque
      (c) Both force and torque
      (d) Neither force nor torque
    3. The dimensional formula of permittivity of free space (ε₀) is:
      (a) [M⁻¹ L⁻³ T⁴ A²]
      (b) [M L³ T⁻⁴ A⁻²]
      (c) [M⁻¹ L⁻³ T⁻⁴ A²]
      (d) [M⁻¹ L³ T⁴ A²]
    4. A charge q is placed at the center of a cube. The electric flux through each face is:
      (a) q/ε₀
      (b) q/6ε₀
      (c) q/4ε₀
      (d) Zero
    5. Electrostatic field lines do not form closed loops because:
      (a) Electric field is conservative
      (b) Electric field is non-conservative
      (c) Charges are scalar
      (d) None
    6. Direction of electric dipole moment is:
      (a) From + to −
      (b) From − to +
      (c) Perpendicular to axis
      (d) Same as electric field
    7. Conservation of total charge of an isolated system is known as:
      (a) Quantization
      (b) Conservation of charge
      (c) Additivity
      (d) Coulomb’s law
    8. If distance between two charges is doubled, force becomes:
      (a) Double
      (b) Half
      (c) Four times
      (d) One-fourth
    9. Electric field due to a short dipole on axial line varies as:
      (a) 1/r
      (b) 1/r²
      (c) 1/r³
      (d) r²

Section – B (Short Answer – I) (5 × 2 = 10 Marks)

  1. Define electric dipole moment. Write its SI unit.

  2. Why do electric field lines never intersect?

  3. State the principle of quantization of charge with formula.

  4. A dielectric sheet is inserted between two charged spheres. What happens to force?

  5. Draw electric field lines of an electric dipole.

Section – C (Short Answer – II) (4 × 3 = 12 Marks)

      1. Derive expression for electric field on equatorial line of a dipole.
      2. State Gauss’s law and prove electric field inside a charged spherical shell is zero.
      3. Show orientation of dipole in uniform electric field for stable and unstable equilibrium.
      4. Charges q are placed at x = 1, 3, 9… Find electric field at origin.

Section – D (Case Study) (1 × 4 = 4 Marks)

        1. An infinite plane sheet has surface charge density σ.
        (i) Expression for electric field
        (ii) Dependence on distance
        (iii) Direction for positive sheet
        (iv) Field between two sheets +σ and −σ

Section – E (Long Answer) (1 × 5 = 5 Marks)

  1.  
(a) Derive electric field due to dipole on axial line.
(b) Plot graph of E vs r for r ≫ a.

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