Electrical Properties of Materials

Daffodil International University Department of Electrical and Electronic Engineering Faculty of Engineering Mid-Term Examination, Fall-2020 Course Code: 0713-215 Course Title: Electrical Properties of Materials Section: A, B, C, D Level-Term: L2-T3 Teacher's Initial: SH Full Marks: 25 Exam Date: October 28, 2020 Time: 1.5 Hours [Notes: Answer all the Questions. The second right most column indicates the course outcomes with respective Bloom's level and right most column indicates the allocated marks] Q1. Briefly explain the generalized molecular bonding theory with neat, clear, and well-labeled diagrams. CO-1 (C2) 4 Q2. A unit cell is shown in the Fig. 1: Cell parameter, a = 0.362 nm a) Find the planner concentration for plane (110). b) Find the planner concentration for plane (111). [Figure: FCC unit cell with atoms at corners and face centers, labeled Fig. 1] CO-1 (C2) 4 Q3. The energy of vacancy formation in the Ge crystal is about 2.2 eV. Calculate the fractional concentration of vacancies in Ge at 938 °C, just below its melting temperature. Estimate the vacancy concentration given that the atomic mass and density of Ge are 72.64 g mol^-1 and 5.32 g cm^-3, respectively. Neglect the change in the density with temperature. CO-1 (C2) 4 Q4. a) Deduce the expression of the electrical conductivity, σ = enμ_e, for a solid using the classical free electron theory. CO-3 (C4) 5 b) Calculate the drift mobility and the mean scattering time of conduction electrons in copper at room temperature, given that the conductivity of copper is 5.9x10^5 Ω^-1cm^-1. The density of copper is 8.96 g cm^-3 and its atomic mass is 63.5 g mol^-1. If the applied electric field is 5 Vcm^-1, estimate the mean free path of conduction electrons between collisions. CO-3 (C3) 4 Q5. Using Fourier's Law of thermal conduction and Ohm's law of resistivity, derive the model for thermal resistivity when heat flows through a solid crystal. CO-3 (C4) 4