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Sample Exam Paper

MPY351Sample Practical Examination — I

Course: Electronics Lab (MPY351)Programme: M.Sc. Physics (Electronics Specialization) — Semester III
Time: 4 HoursMaximum Marks: 100

General Instructions:

  1. The examiner will allot one device-characterization experiment and one circuit-design experiment.
  2. Marks distribution: Circuit connection & readings 40, Graph/calculation 30, Viva-voce 30.
  3. Use the CRO/multimeter provided; do not exceed the rated voltage of any device.
  4. Switch off the supply before altering any circuit connections.

Section A — Short Answer (Compulsory)

  1. What is the cut-in voltage of a silicon diode, and how do you identify it from your plotted graph? (2 marks)
  2. Define current gain β of a BJT in CE configuration. (2 marks)
  3. What is the difference between the ohmic and saturation regions of an FET's drain characteristics? (2 marks)
  4. State the frequency formula for a Colpitts oscillator. (2 marks)
  5. How does a phototransistor differ from a photodiode in operation? (2 marks)
  6. What is the function of a clamper circuit? (2 marks)
  7. Give the formula for the output pulse width of a 555 timer in monostable mode. (2 marks)

Section B — Attempt any two parts of each

  1. Plot the forward and reverse bias V-I characteristics of the given p-n junction diode and determine its cut-in voltage and dynamic resistance. (5 marks)
  2. Plot the input and output characteristics of the given BJT in CE configuration and determine its current gain β. (5 marks)
  3. Set up a Colpitts oscillator on the breadboard, observe the output waveform on a CRO, and compare the measured frequency with the calculated value. (5 marks)
  4. Design a positive clipper and a negative clipper circuit; sketch and explain the input and output waveforms observed. (5 marks)

Section C — Attempt any two questions in full

  1. Explain the theory of p-n junction diode conduction and derive the diode equation. Discuss how static and dynamic resistance are extracted from the experimental V-I curve. (10 marks)
  2. Explain the working of the CE-configuration BJT amplifier stage, and describe how the input/output characteristic curves are used to identify the active, saturation and cut-off regions. (10 marks)
  3. Compare the Colpitts and Hartley oscillator circuits in terms of their feedback networks and derive the frequency of oscillation for each. (10 marks)