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Anandh Subramaniam & Kantesh Balani

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1 Anandh Subramaniam & Kantesh Balani
Diagnostic Test The diagnostic test is meant to check some basic ‘fundas’ to see if you are ready for this course. MATERIALS SCIENCE & ENGINEERING Anandh Subramaniam & Kantesh Balani Materials Science and Engineering (MSE) Indian Institute of Technology, Kanpur URL: AN INTRODUCTORY E-BOOK Part of A Learner’s Guide

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What is the fundamental constituent of the matter we see around? (we are not referring to the fundamental particles!) Atoms (diamond is made carbon atoms), Ions (common salt is made of Na+ and Cl– ions, Molecules (ice is made of H2O molecules). What kinds of bonds exist? The strong bonds are: Covalent, ionic and metallic bonds. The weak interactions include: hydrogen bond and Van der Walls bond. What are the states of matter? How can change in state be brought about? Solid, liquid and gas. Change in state can be brought about by temperature and pressure. In metals the electrical conduction takes place by________. Motion of free electrons. In ionic solids electrical conduction takes places by ______. Motion of cations (vacancies are needed for this) Which of the following bonds has a more ‘directional’ character: covalent, ionic, metallic? Covalent bonds are directional. Temperature is a measure of _______________. The average kinetic energy of the molecules. Which of the two has an ordered structure: crystal or glass. Crystal. Glasses may have short range order but no long range order. Is a Cu wire a single crystal? Cu wire is made of crystalline regions called grains. It is a polycrystal.

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What properties of electromagnetic radiation will make ‘ideal’ diffraction possible? (i) monochromatic source, (ii) coherent radiation, (iii) wavelength of the order of lattice spacing. What can happed if waves impinge on a material? Reflection, transmission, absorption. A combination of these may also occur. What is a vector? A vector, unlike a scalar has both direction and magnitude. In 3 dimensions a vector is specified by 3 numbers. Can we have ‘perfect’ crystals? Crystals can have many defects. 3 of these are unavoidable: Surface, thermal vibration of atoms, vacancies. Why are X-rays used for study of materials? X-rays have wavelength of the order of lattice spacing and can be used for diffraction studies to determine crystal structures. What happens to the internal energy of water when we heat it? The internal energy (E) increases due to increase in translational, rotational and vibrational kinetic energy of water molecules. What are the basic properties associated with an electron? An electron has mass, charge, spin (and hence angular momentum and magnetic moment). How big is an electron? In spite of having the properties mentioned above, the electron is nearly a point (pointlike)- no known dimension to ~1015m.

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What is the difference between a insulator and a semi-conductor? Both have bandgaps. The semiconductor has a small bandgap, such that even at room temperature some electrons can be excited across the bandgap. Give examples of semiconductors. Ge, Si, GaAs, GeSi (they can be elements or compounds). What is a hole? A hole is the vacant state in the valence (energy) band of a semiconductor, when a electron is excited to the conduction band (should not be confused with a vacancy). If Fe is a ferromagnetic material, why is a sample of Fe non-magnetic (unless ‘magnetized’)? The regions where ‘magnetic spins’ are arranged in parallel are called domains. The domains are arranged in such a way as to give a minimum external magnetic field. If microscopy is done with red light or blue light- which one of the two illuminations will give better resolution? Blue light with a shorter wavelength, will give a better resolution. Electrical conductivity of metals will increase or decrease with T? Decrease. Electrons will be scattered more by lattice vibrations. Hence a ‘nearly perfect crystal’ will become a superconductor at 0K. How many dimensions does space have? 3D. But in materials science we often deal with lower dimensional objects which are ‘effectively’ 2D, 1D and 0D. Sometimes even with higher dimensions! What are close packed crystals? Certain arrangement of spheres give a highest volume occupied by matter (of ~74%). Crystals which have this kind of packing are called close packed crystals.

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