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Sample Exam Paper

BAS151Sample Practical Examination — II

Course: Physics Lab (Engineering Physics Laboratory) (BAS151)Programme: B.Tech. — Semester I (Common to all branches)
Time: 3 HoursMaximum Marks: 50

General Instructions:

  1. The examiner will allot one experiment from Group A and one from Group B.
  2. Bring your completed lab record; unrecorded experiments will not be considered for evaluation.
  3. State all formulae used and show unit conversions clearly in the calculation section.
  4. A viva-voce on the theory of both allotted experiments will follow the practical.

Section A — Short Answer (Compulsory)

  1. How is the separation of the two virtual coherent sources determined in Fresnel's biprism experiment? (2 marks)
  2. Why must a diffraction grating spectrometer be adjusted for parallel rays before taking readings? (2 marks)
  3. State Brewster's law and its use in identifying the polarizing angle. (2 marks)
  4. Define retentivity and coercivity with reference to a hysteresis loop. (2 marks)
  5. What is meant by 'end correction' in a bridge experiment, and how does Carey Foster's method eliminate it? (2 marks)
  6. Why is a null-deflection method generally more accurate than a direct-deflection method? (2 marks)
  7. What is meant by attenuation in an optical fibre, and in what unit is it expressed? (2 marks)

Section B — Attempt any two parts of each

  1. Perform the Fresnel's biprism experiment to determine the wavelength of the given monochromatic source. (5 marks)
  2. Determine the wavelength of a given spectral line using a plane transmission grating on a spectrometer. (5 marks)
  3. Trace the hysteresis (B–H) loop of the given ferromagnetic sample and determine its retentivity and coercivity. (5 marks)
  4. Determine the energy band gap of the given semiconductor material from resistance–temperature measurements. (5 marks)

Section C — Attempt any two questions in full

  1. Describe the theory and procedure of Fresnel's biprism experiment. Derive the expression for fringe width and explain the displacement method used to find the separation between the two virtual sources. (10 marks)
  2. Explain the theory of a plane diffraction grating spectrometer. Derive the grating equation and explain how the wavelength of an unknown spectral line is determined experimentally. (10 marks)
  3. Describe how the B–H hysteresis loop of a ferromagnetic sample is obtained experimentally, and explain the physical significance of the enclosed loop area, retentivity and coercivity. (10 marks)