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12th Standard Physics English Medium Electronics and Communication Systems Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
    Multiple Choice Questions
    15 x 1 = 15
  1. Doping a semiconductor results in

    (a)

    The decrease in mobile charge carriers

    (b)

    The change in chemical properties

    (c)

    The change in the crystal structure

    (d)

    The breaking of the covalent bond

  2. The output transducer of the communication system converts the radio signal into ________.

    (a)

    Sound

    (b)

    Mechanical energy

    (c)

    Kinetic energy

    (d)

    None of the above

  3. The forbidden energy band gap in semi conductor, conductor and insulator are E1, E2 and E3 respectively. The relation among them is

    (a)

    E1. < E2 > E3

    (b)

    E1 > E2 > E3

    (c)

    E1 < E2 < E3

    (d)

    E1 > E2 < E3

  4. The radiation of electrical energy is practicable only above _________

    (a)

    20 kHz

    (b)

    200 MHz

    (c)

    200 kHz

    (d)

    20 Hz

  5. Microphone converts __________ energy into ________ energy.

    (a)

    sound, electrical

    (b)

    electrical, magnetic

    (c)

    magnetic, sound

    (d)

    light, heat

  6. In an insulator the energy gap between the conduction band and valence band is of the order of

    (a)

    2MeV

    (b)

    5eV

    (c)

    1eV

    (d)

    10-3eV

  7. Vacant energy levels are called _________

    (a)

    valence level

    (b)

    core level

    (c)

    conduction levels

    (d)

    compound level

  8. The speaker converts ________ energy into ______ energy.

    (a)

    electrical, sound

    (b)

    sound, electrical

    (c)

    light, sound

    (d)

    sound, mechanica

  9. Resistance of any' photosensitive material is ______ to the intensity of light exposed

    (a)

    directly proportional

    (b)

    indirectly proportional

    (c)

    a constant

    (d)

    independent

  10. Zener breakdown is mainly due to ________

    (a)

    collision

    (b)

    breaking of covalent bonds

    (c)

    doping

    (d)

    recombination

  11. When the output is an complement of the input it is ____________

    (a)

    NOT gate

    (b)

    AND gate

    (c)

    OR

    (d)

    NAND

  12. _________ is the most often used wire material.

    (a)

    Copper

    (b)

    Aluminium

    (c)

    Sulphur

    (d)

    iron

  13. ________ wire is used between telephones and the central office

    (a)

    Flat

    (b)

    Multiconnector

    (c)

    Co-axial

    (d)

    Twisted pair

  14. The distance of a geostationary satellite's orbit from the Earth is about _______

    (a)

    366 km

    (b)

    108 km

    (c)

    36 X 103km

    (d)

    30 m

  15. The maximum carrier swing allowed in frequency modulation is :

    (a)

    455 kHz

    (b)

    10.7 kHz

    (c)

    75 MHz

    (d)

    150 kHz

  16. 2 Marks
    10 x 2 = 20
  17. Distinguish between wireline and wireless communication? Specify the range of electromagnetic waves in which it is used.

  18. What does RADAR stand for?

  19. Distinguish between Intrinsic and extrinsic semiconductors.

  20. What do you mean by doping?

  21. Distinguish between avalanche and zener breakdown.

  22. Explain the current flow in a NPN transistor

  23. Give circuit symbol, logical operation, truth table, and Boolean expression of AND, OR, NOT, NAND, NOR, and EX-OR gates

  24. Define energy band

  25. Define Reverse bias.

  26. Mention any three application Zener diode.

  27. 3 Marks
    10 x 3 = 30
  28. Explain the basic elements of communication system with the necessary block diagram.

  29. What do you know about GPS? Write a few applications of GPS.

  30. Fiber optic communication is gaining popularity among the various transmission media -justify,

  31. Draw the circuit diagram' of a half wave rectifier and explain its working

  32. Write notes on Photodiode

  33. Transistor functions as a switch. Explain.

  34. Consider an ideal junction diode. Find the value of current flowing through AB is

  35. Determine the wavelength of light emitted from LED which is made up of GaAsP semiconductor whose forbidden energy gap is 1.875 eV. Mention the colour of the light emitted (Take h = 6.6 × 10-34 Js).

  36. The output characteristics of a transistor connected in common emitter mode is shown in the figure. Determine the value of IC when VCE = 15 V. Also determine the value of IC when VCE is changed to 10 V

  37. Give the Schematic representation of valence band, conduction band, and forbidden energy gap. and draw energy band structure of
    (a) Insulators
    (b) Semiconductors
    (c) Metals?

  38. 5 Marks
    8 x 5 = 40
  39. A transistor having a = 0.99 and VBE = 0.7V collector current, is given in the circuit. Find the value of the collector current.

  40. In the circuit shown in the figure, the input voltage Vi is 20 V, VBE = 0 V and VCE = 0 V. What are the values of IB, IC, β?

  41. Calculate the range of the variable capacitor that is to be used in a tuned-collector oscillator which has a fixed inductance of 150 μH. The frequency band is from 500 kHz to 1500 kHz.

  42. How does the change in temperature and application of electric field affect the behavior of materials and write the range of resistivity for each materials.

  43. Explain current transfer characteristics.

  44. Write any two distinguishing features between Insulators, Metals and semiconductors and. insulators an the basis of energy band diagrams.

  45. For a BJT, the common - base current gain α = 0.98 and the collector base junction reverse bias saturation ICU = 0.6μA. This BJT is connected in the common emitter mode and operated in the active region with a base drive current ID= 20 μA. The collector current IC for this mode of operating is

  46. Write a note on RADAR and its applications.

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