JNTU B.Tech Supplementary 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 experimental setup for measuring Hall voltage.
(b) What are semi-condctors? How do they differ from conductors? Discuss.
Explain about p-type semi-conductors.
3. (a) Differentiate between drift and diffusion currents in semi-conductors. Explain
which is more often present in semi-conductor devices.
(b) Define and explain diffusion constant for electrons. Also give its dimensions.
(c) Explain mean life time of carriers.
4. Distinguish between intrinsic and impurity semi-conductors with suitable examples.
Discuss the theory of intrinsic conductivity of a semi-conductor.
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) Does a large magnetic moment per atom mean a high curie temperature?
(b) Distinguish fully among Ferromagnetism, paramagnetism and diamagnetism.
Also give examples for each of these materials.
7. (a) Distinguish between ferromagnetic, and antiferromagnetic materials. Give examples for each class of materials.
(b) Discuss weiss theory of ferromagnetism bringing out its merits and demerits.
8. (a) Explain why in soft magnetic materials hysteresis loses must be kept down to
a minimum value.
(b) Soft magnetic materials find wide applications requiring frequent reversals of direction of magnetization? Explain why?
(c) Explain the key factors in the design of soft magnets.