JNTU IV B.Tech I Semester Supplimentary Examinations, February 2008
Semi-Conductors And Magnetic Materials
(Metallurgy & Material Technology)
1. Explain with suitable diagrams the conduction band, valence band and the forbidden band and explain the behavior of conductor, semi-conductor and insulator. Explain the contribution of electrons and holes to electrical conduction.
2. (a) Explain the terms
i. Mobility of charge carriers and
ii. Hall effect.
(b) Explain how Hall effect is used to determine the mobility of charge carriers.
(c) Give the principle of Hall effect multiplier.
3. (a) What are energy states? What are density of energy states? Explain density
of energy states in semi-conductors.
(b) What is an intrinsic semi-conductor. explain it in detail with the help of suitable examples.
4. (a) Discuss the method of identifying an unknown piece as n-type or p-type semiconductor.
(b) Intrinsic semiconductors are not suitable for applications in electronic devices – why? Show that the fermi level for a pure germanium lies in the middle of forbidden gap.
5. (a) What is energy gap? Give a rough estimate of band gap in superconductors.
(b) At what temperature the band gap disappears and why? Explain.
(c) What is coherence length? Explain coherance length for electrons in superconductors.
6. (a) Explain how a high initial permeability in Fe-Ni alloys help to reduce the area under hysteresis loop.
(b) Perfect diamagnetism of a material is due to a certain electronic arrangement. Do you think that this electronic arrangement is compatible with zero resistance of super conductors? Explain. Why are not all diamagnetic materials have zero resistance property? Discuss.
7. Obtain an expression for paramagnetic susceptibility of free electrons on the basis of the classical laws. Give an account of the quantum theory of paramagnetism in detail.
8. (a) Why are strain hardened steels also harder magnetically and why are annealed ones softer.
(b) What are ceramic magnets. Explain their working principle. Explain examples for ceramic magnets.
(c) Mention some of the soft magnetic materials. Give their important applications.