Download Y4 SemII Electr.. - UR - College of Science and Technology

KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY
INSTITUTE EXAMINATIONS – ACADEMIC YEAR 2012/2013
MAIN EXAMINATION
FACULTY OF SCIENCE
SCIENCE 2-PHYSICS
B.Sc. in Applied Physics, Material Science Option
YEAR IV, SEMESTER II
PHY3425 Electrical Engineering Materials
DATE:
TIME: 2 HOURS ( )
MAXIMUM MARKS = 60
INSTRUCTIONS
1. This paper contains FOUR (4) questions.
2. Question 1 is compulsory
3. Answer any TWO (2) questions among questions 2,3 and4
4. Each question counts 20 marks.
5. No written materials allowed.
6. Write all answers in the booklet provided.
7. Do not forget to write your Registration Number.
Question 1.
(i).
(ii).
(iii).
(iv).
How do the temperature and impurities affect the electrical resistivity of:
a. metals ?
b. semiconductors?
Justify your answer.
(4 marks)
Distinguish extrinsic semiconductor and intrinsic semiconductor. Explain why at
a high temperature an extrinsic semiconductor behaves like an intrinsic one.
(5 marks)
Give the analogy between ferroelectric and ferromagnetic materials with respect
to their dielectric and magnetic properties
(6marks)
What is superconductivity? Explain briefly two types of superconductors
(5 marks)
Question 2
(i).
(ii).
(iii).
(iv).
a. Give the reason of the following.: ‘In the absence of external electric field,
though electrons will be moving due to thermal agitation, it does not give rise to a
current in a conductor.’
b. Define the drift velocity and the mobility of charge carriers (4 marks)
Define the terms: valence band, conduction band and forbidden band (6 marks)
Distinguish between conductors, insulators and semiconductors (6 marks)
Mobilities of electrons and holes in a sample of intrinsic germanium at room
temperature are 3600 cm2 /V.s and 1700 cm2 /V.s respectively. If the electron and
holes densities are each equal to 2.5 x 1013 /cm3 , calculate its conductivity)
(4 marks)
Question 3
(i).
(ii).
(iii).
(iv).
Question 4
(i).
Describe the different mechanisms of polarization
(6 marks)
Distinguish between electrostriction and the reverse piezoelectric effect
(4 marks)
How are magnetic materials classified? Explain the different type of magnetic
materials
(6 marks)
What are hard and soft magnetic materials? Compare them on the basis of
hysteresis curves. Give some applications for each type.
(4 marks)
Explain the effect of a magnetic field on superconducting properties of materials
and Meissner - Ochsenfeld effect
(5 marks)
(ii).
(iii).
Discuss the BCS theory of superconductivity
(5 marks)
Explain what are the critical magnetic field and the critical temperature for a
superconductor. Give the relation between them.
(5 marks)
(iv).
Give the important applications of superconductivity
GOOD LUCK!
2
(5 marks)