BASIC ELECTRONICS - B.Tech 3rd Semester Exam., 2020 (New Course)

2020•Semester 2•Civil-CA•End Semester
Bihar Engineering University, Patna
B.Tech 3rd Semester Exam., 2020 (New Course)

BASIC ELECTRONICS

Time: 03 HoursCode: 104301Full Marks: 70

Instructions:

  1. The marks are indicated in the right-hand margin.
  2. There are NINE questions in this paper.
  3. Attempt FIVE questions in all.
  4. Question No. 1 is compulsory.
Q.1 Choose the correct option of the following (any seven):[14]

  1. Which of the following expressions represents the correct formula for the density of electrons occupying the donor level?

    1. \( n_d = N_d - N_d^+ \)
    2. \( n_d = N_d - N_d \)
    3. \( n_d = N_d + N_d^+ \)
    4. \( n_d = N_d + N_d^- \)

  2. What is the ripple factor of a half-wave rectifier?

    1. 0.31
    2. 0.48
    3. 0.707
    4. 1.21

  3. Which of the following is true about the resistance of a Zener diode?

    1. It has an incremental resistance
    2. It has dynamic resistance
    3. The value of the resistance is the inverse of the slope of the i-v characteristics of the Zener diode
    4. All of the above

  4. Which of the following is true in construction of a transistor?

    1. The collector dissipates lesser power
    2. The emitter supplies minority carriers
    3. The collector is made physically larger than the emitter region
    4. The collector collects minority charge carriers

  5. Consider the following statements: A clamper circuit
    1. adds or subtracts a d.c. voltage to a waveform
    2. does not change the waveform
    3. amplifies the waveform
    Which are correct?

    1. 1, 2
    2. 1, 3
    3. 1, 2, 3
    4. 2, 3
    5. None of the above

  6. For what kind of amplifications can the active region of the common-emitter configuration be used?

    1. Voltage
    2. Current
    3. Power
    4. All of the above

  7. How does the FET operate before the pinch-off region with small value of drain-to-source voltage in accordance to the control of drain-to-source resistance by the bias voltage?

    1. As a voltage controlled resistor
    2. As a voltage dependent resistor
    3. As a voltage variable resistor
    4. All of the above

  8. A Junction FET can operate in

    1. depletion mode only
    2. enhancement mode only
    3. depletion and enhancement modes
    4. neither depletion nor enhancement mode

  9. Which of the following is not a property of an ideal operational amplifier?

    1. Zero input impedance
    2. Infinite bandwidth
    3. Infinite open-loop gain
    4. Zero common-mode gain or conversely infinite common mode-rejection

  10. Which among the following is the major responsible reason for the cause of 'slew rate'?

    1. Current limiting
    2. Saturation of internal stages due to application of high frequency and amplitude signal
    3. Both (i) and (ii)
    4. None of the above
Q.2 Solve both questions :[14]

  1. Draw potential energy diagrams for a forward as well as a reverse-biased p-n junction and explain the flow of currents in both the cases.

  2. The p-silicon has resistivity of \( 100 \text{ }\Omega\text{ cm} \). The other parameters for silicon are: Intrinsic carrier density, \( n_i = 10^{10} \text{ cm}^{-3} \), Hole mobility, \( \mu_p = 500 \text{ cm}^2/\text{V.s} \) and Electron mobility, \( \mu_n = 1200 \text{ cm}^2/\text{V.s} \). Calculate the number of electrons for every 5000 million holes in the semiconductor.

Q.3 Solve both questions :[14]

  1. Determine \( v_0 \) and the required PIV rating of each diode for the configuration of the following figure. In addition, determine the maximum current through each diode.

    Question Diagram

  2. The circuit shown below uses a 9V Zener diode. If the load resistance \( R_L \) is equal to \( 1.5 \text{ k}\Omega \) and the d.c. source equals 24 V, find the maximum value of resistor R required to maintain constant voltage of 9 V across the load.

    Question Diagram
Q.4 Solve both questions :[14]

  1. Draw the cross-sectional view of an n-p-n transistor and explain its operation in active region of operation. What are the different current components of the transistor? How can one use a transistor as amplifier?

  2. Define \( \alpha_{dc} \) and \( \beta_{dc} \). Derive the relationship between \( \alpha_{dc} \) and \( \beta_{dc} \). If the base current in a transistor is \( 30 \text{ }\mu\text{A} \) when the emitter current is 7.2 mA, what are the values of \( \alpha_{dc} \) and \( \beta_{dc} \)? Also, calculate the collector current.

Q.5 Solve both questions :[14]

  1. Draw and explain the input and output characteristics of CB configuration. Where can we use the CB configuration in a transistor circuit? Explain with proper justification.

  2. Design a collector to base bias circuit shown in the figure below for the specified conditions: \( V_{CC} = 15\text{V} \), \( V_{CE} = 5\text{V} \), \( I_C = 5 \text{ mA} \), \( \beta = 150 \).

    Question Diagram
Q.6 Solve both questions :[14]

  1. Draw the structure of JFET and discuss its working. What is pinch-off voltage? How to get its value experimentally?

  2. For the voltage-divider configuration of the figure shown below, determine: (i) \( I_{DQ} \) and \( V_{GSQ} \) (ii) \( V_D \) and \( V_S \).

    Question Diagram
Q.7 Solve both questions :[14]

  1. Define an ideal operational amplifier. Draw the approximate block diagram of an OPAMP giving various stages of the amplifier.

  2. Find the output voltage of the following OPAMP circuit.

    Question Diagram
Q.8 Solve both questions :[14]

  1. Draw the gain-frequency response of an RC coupled amplifier. Discuss fall in gain at very low and at very high frequencies.

  2. Common emitter (CE) amplifier shown in the figure has voltage gain of 150 when \( R_E = 0 \). Stability is brought through negative feedback by adding resistor \( R_E \). Calculate the value of resistor \( R_E \) using feedback concepts so that final voltage gain \( (=A_{FB}) \) is equal to 100.

    Question Diagram
Q.9 Solve both questions :[14]

  1. Explain the construction and working principle of a photo diode (PD).

  2. Explain the construction and working principle of an SCR. Write the applications utilizing SCR.