Important Questions on Solid State
Explain why does the presence of Frenkel defects not affect the density of a crystal. 
How do the Schottky and Frenkel defects increase the conductivity of a crystal? How does a crystal having metal excess defect maintain its electrical neutrality? Why does a crystal of appear violet in spite of the fact that both and ions are colourless? What are F-centres, and how do they impart colour to a crystal? What is doping? Why does the impurity-doped silicon act as a semiconductor? What are semiconductors? What factors are responsible for the conduction of current by a semiconductor? Mention their important applications. What is ferromagnetism, and how does it arise? 
