Physics Group - II (3110018)

BE | Semester 1 
  Winter - 2019|02-01-2020
Total Marks 70

Q1 (a) Enlist the assumptions of free electron theory.

 Unit : Electronic Materials |  Topic : Free electron theory

Q1 (b) Give the difference between Direct and Indirect band gap.

 Unit : Electronic Materials |  Topic : E-k diagram, Direct and indirect bandgaps

Q1 (c) Explain forward and reverse bias conditions in PN junction diode.

 Unit : Semiconductors |  Topic : Carrier generation and recombination, Carrier transport: diffusion and drift, p-n junction

Q2 (a) Define Intrinsic and extrinsic semiconductor.

 Unit : Semiconductors |  Topic : Intrinsic and extrinsic semiconductors

Q2 (b) The thermal and electrical conductivity of Cu at 20°C Kare 390 W m-1 K-1 and 5.87 x 107 (Ω m)-1 respectively. Calculate the Lorentz number.

 Unit : Electronic Materials |  Topic : Free electron theory

Q2 (c) Explain Schottky diode in detail.

 Unit : Semiconductors |  Topic : Metal-semiconductor junction (Ohmic and Schottky), Semiconductor materials of interest for optoelect

OR

Q2 (c) Explain the dependence of Fermi level on temperature.

 Unit : Semiconductors |  Topic : Dependence of Fermi level on carrier-concentration and temperature (equilibrium carrier statistics)

Q3 (a) Explain Drude model.

 Unit : Light-Semiconductor Interaction |  Topic : Drude model

Q3 (b) Fermi energy of a given substance is 7.9 eV. What is the average energy and speed of electron in this substance at 0 K?

 Unit : Electronic Materials |  Topic : Fermi level, Effective mass, Phonons.

Q3 (c) Explain photovoltaic effect. With required diagrams discuss construction and working of solar cell.

 Unit : Light-Semiconductor Interaction |  Topic : Optical loss and gain; Photovoltaic effect, Exciton

OR

Q3 (a) Write a short note on excition.

 Unit : Light-Semiconductor Interaction |  Topic : Optical loss and gain; Photovoltaic effect, Exciton

Q3 (b) Consider two-dimensional square lattice of side 3.0 Å. At what electron momentum values do the sides of first Brillouin zone appear? What is the energy of free electron with this momentum?

 Unit : Electronic Materials |  Topic : Free electron theory

Q3 (c) Derive an equation of joint density of states.

 Unit : Light-Semiconductor Interaction |  Topic : Joint density of states

Q4 (a) Define Hall effect. Give its physical significance.

 Unit : Measurements |  Topic : Four-point probe and Van Der Pauw measurements for carrier density

Q4 (b) 2.0 cm wide and 1.0 mm thick copper strip is placed in a magnetic field 1.5 Wb/m2 perpendicular to the strip. Suppose a current of 200 A is set up in the strip what will be the Hall potential appeared across the strip? (n = 8.4 x 1028 electrons/m3). 

 Unit : Measurements |  Topic : Four-point probe and Van Der Pauw measurements for carrier density

Q4 (c) Discuss UV-VIS method for band gap measurement of semiconductor.

 Unit : Measurements |  Topic : band gap by UV-Vis spectroscopy, absorption/transmission

OR

Q4 (a) Discuss Fermi golden rule.

 Unit : Light-Semiconductor Interaction |  Topic : Density of states for photons

Q4 (b) The transmitted intensity is 0.4 times intensity of incident light. If this light is incident on a semiconductor having a thickness of 0.5 cm then find absorption coefficient. 

 Unit : Measurements |  Topic : band gap by UV-Vis spectroscopy, absorption/transmission

Q4 (c) Explain four probe method. Derive an equation to calculate resistivity of a thin sample.  

 Unit : Measurements |  Topic : Four-point probe and Van Der Pauw measurements for carrier density

Q5 (a) Write short note cryotron.

 Unit : Superconductivity |  Topic : Josephson's junction and its application Application of superconductors

Q5 (b) Explain London's penetration depth.

 Unit : Superconductivity |  Topic : Penetration depth : Magnetic field

Q5 (c) Give the difference between type 1 and type 2 superconductor.

 Unit : Superconductivity |  Topic : Properties of superconductor

OR

Q5 (a) Write short note on SQUID.

 Unit : Superconductivity |  Topic : Josephson's junction and its application Application of superconductors

Q5 (b) Calculate the critical current for a superconducting wire of lead having a diameter of 2 mm at 2 K. Critical temperature for lead is 4 K and Hc(0) = 6.5 X 104 A/m.

 Unit : Superconductivity |  Topic : Effect of magnetic field

Q5 (c) Explain the properties of superconductors in detail. 

 Unit : Superconductivity |  Topic : Properties of superconductor