# Engineering Materials

Engineering Materials
1, (a) A 10-mm-diameter Brinell hardness indenter produced an indentation 1.62 mm in diameter in a steel alloy when a load of 500 kg was used. Compute the HB of this
material.
(b) What will be the diameter of an indentation to yield a hardness of 450 HB when a 500 kg load is used

2. Cite five factors that lead to scatter in measured material properties.

3. A large tower is to be supported by a series of steel wires. It is estimated that the load on eachwire will be 11,100 N (2500 lbf). Determine the minimum
required wire diameter assuming a factorof safety of 2 and a yield strength of 1030 MPa (150,000 psi).

4. (a) Compute the electrical conductivity of a 5.1-mm (0.2-in.) diameter cylindrical silicon specimen51 mm (2 in.) long in which a current of 0.1 A passes in an
axial direction. A voltage of 12.5 V ismeasured across two probes that are separated by 38 mm (1.5 in.).
(b) Compute the resistance over the entire 51 mm (2 in.) of the specimen.

5. In a semiconductor, what charge carriers are present

6. To what temperature would 25 lbm of a 1025 steel specimen at 25°C (77°F) be raised if 125 Btu ofheat is supplied

7. A 0.1 m (3.9 in.) rod of a metal elongates 0.2 mm (0.0079 in.) on heating from 20 to 100°C (68 to212°F). Determine the value of the linear coefficient of thermal
expansion for this material.
8. (a) Explain the two sources of magnetic moments for electrons.
(b) Do all electrons have a net magnetic moment Why or why not
(c) Do all atoms have a net magnetic moment Why or why not
9. Briefly explain why metals are opaque to electromagnetic radiation having photon energies withinthe visible region of the spectrum.

10. Can a material have an index of refraction less than unity Why or why not
11. Briefly explain what determines the characteristic color of (a) a metal and (b) a transparentnonmetal.

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