material science class 4 data for all aspirants.

Fracture :

Fracture is the separation of a specimen into two or more parts by an applied stress. Fracture can occur under all service conditions. Materials subjected to extended cyclic loading may result in fatigue fracture (delayed fracture). Also under the influence of a constant applied stress many materials continue to deform indefinitely.

This process is called creep. It is an important consideration in high temperature applications. Prevention of failure during service is one of the most important problems faced by the engineers.

Resistors

The main function of resistors in a circuit is to control the flow of current to other components.

 

 

Semi conductors

 *Their electrical properties are intermediate when compared with electrical conductors and electrical insulators.

 *These electrical characteristics are extremely sensitive to the presence of minute amounts of foreign atoms.

• Found very many applications in electronic devices over decades through integrated circuits. In can be said that semiconductors revolutionized the electronic industry for last few decades.

Dielectric properties

Dielectric is a material separating two charged bodies. For a material to be a good dielectric, it must be an electrical insulator. Dielectric materials are used in capacitors, devices used to store the electric energy.
 *Energy stored, Q, between two plates having area, A, charged by voltage, V, separated at a distance, l, in vacuum is given by
where ε0 – permitivity of vacuum (8.85 X 10-12 F/m)
* For a dielectric material, ε = εr ε0
* εr value is always greater than ‘1’, as a result of polarization.

magnetic properties:

Magnetic properties play an important role in daily life. Magnetic materials are used in electric motors, generators, transformers. Modern-day devices use data storage technology that is based on magnetic particles. Magnetic materials are used in devices like telephones, televisions, supercomputers, etc. they are also used in medical technology, for example DNA sequencing. This chapter deals with the genesis of magnetism, different types of magnetism, and finally different types of magnets.

Multiple Choice Questions’ Bank:

1. Basic source of magnetism ______________.

(a) Charged particles alone (c) Magnetic dipoles

(b) Movement of charged particles (d) Magnetic domains

2. Units for magnetic flux density
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m

3. Magnetic permeability has units as
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m

4. Magnetic permeability has units as
(a) Tesla (b) Henry (c) Tesla / m (d) Henry / m

5. Magnetic field strength’s units are
(a) Wb / m2 (b) Wb / A.m (c) A / m (d) Tesla / m

6. Example for dia-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites

 

 

7. Example for para-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites

8. Example for ferro-magnetic materials
(a) super conductors (b) alkali metals (c) transition metals (d) Ferrites

9. Example for anti-ferro-magnetic materials
(a) salts of transition elements (b) rare earth elements (c) transition metals (d) Ferrites

10. Example for ferri-magnetic materials
(a) salts of transition elements (b) rare earth elements (c) transition metals (d) Ferrites

 

questions 11-18

11. Magnetic susceptibility para-magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2

12. Magnetic susceptibility dia–magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2

13. Magnetic susceptibility ferro-magnetic materials is
(a) +10-5 (b) -10-5 (c) 105 (d) 10-5 to 10-2

14. Typical size of magnetic domains ______ (mm).
(a) 1-10 (b) 0.1-1 (c) 0.05 (d) 0.001

15. Typical thickness of Bloch walls ______ (nm).
(a) 0.1-1 (b) 1-10 (c) 10-50 (d) 100

16. Example for soft magnet
(a) 45 Permalloy (b) CrO2 (c) Fe-Pd (d) Alnico

17. Example for hard magnet
(a) 45 Permalloy (b) CrO2 (c) Fe-Pd (d) Alnico

18. Example for magnetic material used in data storage devices
(a) 45 Permalloy (b) CrO2 (c) Cunife (d) Alnico

Answers:
1. b
2. a
3. b
4. d
5. c
6. a
7. b
8. c
9. a
10. d
11. d
12. b
13. c
14. c
15. d
16. a
17. d
18. b

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