EXAMSHARE

Western Delta University, Oghara Delta State

department of physics with electronics
college of natural and applied sciences
western delta university

second semester examination 2022/2023 session

PHY104 - General Modern Physics time: 2hrs

answer question ONE and any other TWO questions

  1. Question 1 (Compulsory)

    1. A tungsten filament consists of a cylindrical cathode 5cm long and 0.01cm in diameter. If the operating temperature is 2500K, find the emission current density, given that the Richardson constant = 60.2 X 104 A/m2/K2, the work function ø = 4.517eV (7.5 marks)
    2. Sketch and briefly explain the graph for:
      1. Kinetic energy versus frequency
      2. Photocurrent versus intensity
      (6 marks)
    3. List three properties of Xray. (4.5 marks)
    4. Briefly explain why a radium sticker grows in the dark. (6 marks)
    5. Sketch the circuit symbols of an NPN and PNP transfer showing the directions of the various currents. (6 marks)

  2. Question 2

    1. Briefly explain photoelectric effect. (6 marks)
    2. Calculate the wavelength of a photon which has an energy of 2.4eV (Plancks constant = 6.62 X 10-34 Js, speed of light = 3X108m/s) (6.5 marks)
    3. Given that λth is the threshold wavelength for photoelectric effect to take place. If light of wavelength λ is shone on a material, explain what happens when:
      1. λ < λth
      2. λ > λth
      3. λ = λth
      (7.5 marks)

  3. Question 3

    1. Sketch and briefly explain the Bohrs model of an atom. (6 marks)
    2. Briefly discuss the two ways through which Xrays can be produced. (9 marks)
    3. An Xray tube works on 60,000V. Calculate the minimum wavelength of the Xray emitted in it. (6 marks)

  4. Question 4

    1. Radioactivity results from instability of the nucleus. Highlight the conditions that can lead to this instability. (7.5 marks)
    2. Briefly explain Beta decay. (5 marks)
    3. The half-life period of radium is 1620 years. In how many years will one gram of pure radium lose one centigram. (7.5 marks)

  5. Question 5

    1. Write short notes on the following:
      1. majority carriers
      2. minority carriers
      3. depletion layer
      (7.5 marks)
    2. With the aid of appropriate sketches with circuit symbols, briefly explain forward and reverse bias for a PN junction diode. (5 marks)
    3. Briefly discuss the structure of a bipolar junction transistor. (7.5 marks)