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ECE :: Electronic Devices and Circuits

  1. The ratio of impurity atoms to intrinsic semiconductor atoms in an extrinsic semiconductor is about.

  2. A.
    1 : 10
    B.
    1 : 1000
    C.
    1 : 100000
    D.
    1 : 108

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  3. To ensure that a zener diode does not get destroyed

  4. A.
    the applied voltage should not exceed breakdown voltage
    B.
    the current should not exceed rated current
    C.
    the current should be less than magnitude of barrier potential
    D.
    both (a) and (b)

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  5. SCR turns of from conducting state to blocking state on

  6. A.
    reducing gate current
    B.
    reversing gate voltage
    C.
    reducing anode current below holding current value
    D.
    applying ac to the gate

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  7. The kinetic energy of free electrons in a metal is (where k is the de-Broglie wave number of the electron)

  8. A.
    inversely proportional to k
    B.
    inversely proportional to square of k
    C.
    proportional to k
    D.
    proportional to the square of k

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  9. The turn on time of an SCR is 5 micro second. Its trigger pulse should have

  10. A.
    short rise time with pulse width = 2.5 μs
    B.
    long rise time with pulse width = 3 μs
    C.
    short rise time with pulse width = 4 μs
    D.
    long rise time with pulse width = 4 μs

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  11. The cut in voltage

  12. A.
    is the same for silicon and germanium diodes
    B.
    is a forward voltage
    C.
    is a reverse voltage
    D.
    is a forward voltage below which the current is very small

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  13. With an ac input from 50 Hz power line, the ripple frequency is

  14. A.
    50 Hz in the dc output of half wave as well as full wave rectifier
    B.
    100 Hz in the dc output of half wave as well as full wave rectifier
    C.
    50 Hz in the dc output of half wave and 100 Hz in the dc output of full wave
    D.
    100 Hz in the dc output of half wave and 50 Hz in the dc output of full wave

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  15. For an insulating material, dielectric strength and dielectric loss should be respectively

  16. A.
    high and high
    B.
    low and high
    C.
    high and low
    D.
    low and low

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  17. Semiconductors have

  18. A.
    aero temperature coefficient of resistance
    B.
    positive temperature coefficient of resistance
    C.
    negative temperature coefficient of resistance
    D.
    none of the above

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  19. The dipole moment per unit volume as a function of E in the case of an insulator is given by (symbols have the usual meaning).

  20. A.
    P = ε0E (εr - E)
    B.
    P = ε0E
    C.
    P =
    D.
    P =

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