# 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

## 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

## 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

## 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 (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