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12th Standard English Medium Physics Reduced syllabus Three mark important Questions - 2021(Public Exam )

12th Standard

    Reg.No. :


Time : 01:00:00 Hrs
Total Marks : 75

    3  Marks

    25 x 3 = 75
  1. Calculate the number of electrons in one coulomb of negative charge.

  2. Calculate the electrostatic force and gravitational force between the proton and the electron in a hydrogen atom. They are separated by a distance of 5.3 × 10-11 m. The magnitude of charges on the electron and proton are 1.6 × 10-19 C. Mass of the electron is me = 9.1 × 10-31 kg and mass of proton is mp = 1.6 × 10-27 kg.

  3. The following pictures depict electric field lines for various charge configurations.

    (i) In figure (a) identify the signs of two
    charges and find the ratio \(\left| \frac { { q }_{ 1 } }{ { q }_{ 2 } } \right| \)
    (ii) In figure (b), calculate the ratio of two positive charges and identify the strength of the electric field at three points A, B, and C
    (iii) Figure (c) represents the electric field lines for three charges. If q2 = -20 nC, then calculate the values of q1 and q3.

  4. Define ‘Electric field’ and discuss its various aspects.

  5. Obtain an expression for potential energy due to a collection of three point charges which are separated by finite distances.

  6. Obtain the expression for electric field due to an charged infinite plane sheet.

  7. Compute the current in the wire if a charge of 120 C is flowing through a copper wire in 1 minute.

  8. A copper wire of cross-sectional area 0.5 mm2 carries a current of 0.2 A. If the free electron density of copper is 8.4 × 1028 m-3 then compute the drift velocity of free electrons.

  9. A potential difference across 24 Ω resistor is 12 V. What is the current through the resistor?

  10. Calculate the equivalent resistance between A and B in the given circuit.

  11. Let the magnetic moment of a bar magnet be \(\overset { \rightarrow }{ { p }_{ m } } \) whose magnetic length is d = 2l and pole strength is qm. Compute the magnetic moment of the bar magnet when it is cut into two pieces
    (a) along its length
    (b) perpendicular to its length.

  12. The following figure shows the variation of intensity of magnetisation with the applied magnetic field intensity for three magnetic materials X, Y and Z. Identify the material X,Y and Z.

  13. Explain the principle and working of a moving coil galvanometer.

  14. A cylindrical bar magnet is kept along the axis of a circular solenoid. If the magnet is rotated about its axis, find out whether an electric current is induced in the coil.

  15. A solenoid of 500 turns is wound on an iron core of relative permeability 800. The length and radius of the solenoid are 40 cm and 3 cm respectively. Calculate the average emf induced in the solenoid if the current in it changes from 0 to 3 A in 0.4 second.

  16. Show that the mutual inductance between a pair of coils is same (M12 = M21).

  17. Explain the Maxwell’s modification of Ampere’s circuital law.

  18. Light travelling through transparent oil enters in to glass of refractive index 1.5. If the refractive index of glass with respect to the oil is 1.25, what is the refractive index of the oil?

  19. What is the radius of the illumination when seen above from inside a swimming pool from a depth of 10 m on a sunny day? What is the total angle of view? [Given, refractive index of water is 4/3]

  20. If the focal length is 150 cm for a glass lens, what is the power of the lens?

  21. Briefly explain the principle and working of electron microscope.

  22. Light of wavelength 390 nm is directed at a metal electrode. To find the energy of electrons ejected, an opposing potential difference is established between it and another electrode. The current of photoelectrons from one to the other is stopped completely when the potential difference is 1.10 V. Determine i) the work function of the metal and ii) the maximum wavelength of light that can eject electrons from this metal

  23. Discuss the process of nuclear fusion and how energy is generated in stars?

  24. What are the possible harmful effects of usage of Nanoparticles? Why?

  25. Discuss diffraction at single slit and obtain the condition for nth minimum.


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